Slr Cameras Ebook

Photography Masterclass

This online training course can teach you how to take amazing, eye-catching photos that people will not believe are from you and not a professional photographer! If you own a DSLR camera still are not satisfied with the quality of photos that you are getting from your camera, that is not your fault! You are not to blame for this! Once you learn the proper technique for taking photos, you will be Shocked at the difference that you will see in your photos. You will go from low-quality, lackluster photos to beautiful, high-quality stunners! Don't be discouraged; go through this training program and start learning how to take really amazing quality photos with your DSLR camera! You will learn how to use the best equipment, how to master angles, and how to get the best out of the camera that you have to take the best photos ever! Read more...

Photography Masterclass Summary


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I've really worked on the chapters in this ebook and can only say that if you put in the time you will never revert back to your old methods.

In addition to being effective and its great ease of use, this eBook makes worth every penny of its price.

Is a DSLR right for you

All of this assumes that a DSLR is the best astrocamera for your purposes. Maybe it isn't. Before taking the plunge, consider how DSLRs compare to other kinds of astronomical cameras (Table 1.4, Figure 1.4). Notice that the DSLR provides Figure 1.4. Left to right a film SLR, a DSLR, a webcam modified for astronomy, and an astronomical CCD camera. Figure 1.4. Left to right a film SLR, a DSLR, a webcam modified for astronomy, and an astronomical CCD camera. Digital SLRs have the same vibration problem since the shutter works the same way. For that reason, DSLRs are not ideal for lunar and planetary work. Non-SLR digital cameras, with their tiny, vibration-free leaf shutters, work much better, though they aren't suitable for any kind of deep-sky work because of their tiny, noisy sensors. For deep-sky work and professional astronomical research, the gold standard is the thermoelectrically cooled astronomical CCD camera. These cameras are appreciably harder to use they work only with a...

Imaging with Digital SLR Cameras

Digital cameras offer an attractive alternative to the astronomical CCD camera. Not only are they far less expensive (on a cost-per-megapixel basis), but they produce color images without the hassle of shooting separate filtered images. Digital SLRs offer the added advantage of being easy to use with a wide range of standard camera lenses, as well with telescopes. They have excellent technical specifications. Readout noise is typically under 10 electrons r.m.s., and dark current is low enough to allow exposures of four minutes or longer, depending on the ambient temperature. The full-well capacity tends to be shallow, but it is fully utilized when the CCD or CMOS sensors are digitized and stored in a 12-bit raw format. The greatest drawback from the standpoint of astronomical imaging with standard off-the-shelf digital SLRs is the integral color-balancing filter. This filter blocks the infrared and severely attenuates red light however, special astronomical versions of digital SLRs...

Telephoto Conversion Lenses

Rather than the afocal method through the telescope, a wider field can be realized with a digital camera by using a telephoto conversion lens. These lenses screw into the filter adapters of many digital camera models. The camera is then mounted piggyback on the telescope as shown in Figure 5.3. Most of these lenses increase the focal length of the fixed camera lens by a factor of two. A typical digital camera lens has a focal length of around 24 mm when zoomed to 3x. A telephoto conversion lens will produce an effective focal length of 48 mm. With a 7.2 x 5.3 mm detector the resulting field width is 8.6 . This is equivalent to a 232-mm telephoto lens on a 35-mm film camera. The limiting photographic magnitude for a 30-second exposure with these conversion lenses Figure 5.3. A digital camera with a telephoto adapter mounted on an 80-mm f 5 refractor. Figure 5.3. A digital camera with a telephoto adapter mounted on an 80-mm f 5 refractor.

Digital SLR Image Processing

The latest developments in IRIS software have been targeted at digital SLR camera usage. The widespread development of detectors in large sizes, with high performance and low cost, is a direct result of the fierce competition in the digital SLR camera marketplace. Digital SLR cameras are simple to employ at the focal plane of our telescope. CCD cameras, optimized for astronomy, are still the best for studies requiring maximum performance, such as deep-sky surveys, but digital cameras have other advantages. These advantages include a single unit, compact size, optical viewfinder and a high-performance, film-sized, color CCD CMOS sensor. In addition, their cost is falling almost monthly, already becoming much much cheaper than a dedicated CCD camera. The large size of the sensor used can be quite decisive for some scientific studies like nova detection. Overall, digital cameras are not in competition with CCD cameras but rather are complementary. The image coming out of such digital SLR...

Monolithic Cmos Sensors

Monolithic CMOS sensors are image sensor chips that combine the photodetectors and the readout circuitry on the same piece of silicon. Compared to hybrid FPAs, monolithic arrays are less expensive to manufacture, but the sensitivity is limited to the visible and near infrared wavelength range. Over the course of the last decade, monolithic CMOS technology has made significant improvements. In recent years, a large number of consumer products, including cell phones, digital cameras, and camcorders, have been replacing CCDs with CMOS sensors for the sake of smaller, cheaper, and lower-power systems. A monolithic CMOS sensor is also called an APS. In a monolithic CMOS sensor, the photodiodes share the pixel area with the transistors. For that reason, the fill factor is always less than 100 . In addition, most CMOS imagers are front side illuminated. This limits the sensitivity in the red because of a relatively shallow absorption material. A typical quantum efficiency (QE) plot for a...

Telephoto and retrofocus lenses

Very long telephoto lenses often work like a telescope with a Barlow lens (Figure 7.12, upper right). Technically speaking, telephoto means a lens whose focal length is much longer than its physical length, and the classic achromat-with-Barlow design is the standard way of achieving this, although asymmetrical triplets and asymmetrical double Gauss designs can do the same thing to a lesser degree. The opposite of a telephoto is a retrofocus wide-angle lens, one whose lens-to-film distance is longer than its focal length. To leave room for the mirror, the lens of an SLR can be no closer than about 50 mm from the sensor. To get an effective focal length of, say, 28 mm, the wide-angle lens has to work like a backward telescope it is a conventional lens with a large concave element in front of it.

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Architecture of CMOS Image Sensors

Mono Cmos Sensor Read Out Diagram

In addition to the basic concept of active pixels, a number of common features can be found in most CMOS-based imagers. As shown in Fig. 2, two different scanners surround the actual pixel array a vertical scanner to control the row selection, and a horizontal scanner to amplify and multiplex the analog pixel signals. While most CMOS imagers include comparable vertical scanners, they differ quite substantially in the architecture of the horizontal scanner. Low-speed astronomy detectors typically use a row of analog switches controlled by a simple digital shift register. Faster image sensors require additional circuitry in each column like sample hold stages or column buffers. In some cases, even the A D conversion is integrated into the horizontal scanner as a part of the column structure. Figure 2. Block diagram of a generic CMOS sensor. Figure 2. Block diagram of a generic CMOS sensor. Most CMOS sensors include additional circuitry for bias generation, timing control, and A D...

Practical Amateur Astronomy Digital SLR Astrophotography

In the last few years, digital SLR cameras have taken the astrophotography world by storm. It is now easier to photograph the stars than ever before They are compact and portable, easy to couple to special lenses and all types of telescopes, and above all, DSLR cameras are easy and enjoyable to use. In this concise guide, experienced astrophotography expert Michael Covington outlines the simple, enduring basics that will enable you to get started, and help you get the most from your equipment. He covers a wide range of equipment, simple and advanced projects, technical considerations, and image processing techniques. Unlike other astrophotography books, this one focuses specifically on DSLR cameras, not astronomical CCDs, non-DSLR digital cameras, or film. This guide is ideal for astrophotographers who wish to develop their skills using DSLR cameras and as a friendly introduction to amateur astronomers or photographers curious about photographing the night sky. Further information,...

The DSLR revolution

A few years ago, I said that if somebody would manufacture a digital SLR camera (DSLR) that would sell for under 1000 and would work as well as film for astrophotography, I'd have to buy one. That happened in 2004. The Canon Digital Rebel and Nikon D70 took the world by storm, not only for daytime photography but also for astronomy. Within two years, many other low-cost DSLRs appeared on the market, and film astrophotographers switched to DSLRs en masse. There had been DSLRs since 1995 or so, but Canon's and Nikon's 2004 models were the first that worked well for astronomical photography. Earlier digital cameras produced noisy, speckled images in long exposures of celestial objects. Current DSLRs work so well that, for non-critical work, you almost don't need any digital image processing at all - just use the picture as it comes out of the camera (Figure 1.1). The results aren't perfect, but they're better than we often got with film. As you move past the beginner stage, you can do...

What is a DSLR

A DSLR is a digital camera that is built like a film SLR (single-lens reflex) and has the same ability to interchange lenses. You can attach a DSLR to anything that will form an image, whether it's a modern camera lens, an old lens you have adapted, or a telescope, microscope, or other instrument. Unlike other digital cameras, a DSLR does not normally show you a continuous electronic preview of the image. Instead, the viewfinder of a DSLR uses a mirror and a focusing screen to capture the image optically so that you can view and focus through an eyepiece. When you take the picture, the mirror flips up, the image sensor is turned on, and the shutter opens. The reason a DSLR doesn't show the electronic image continuously is that its sensor is much larger than the one in a compact digital camera. Big sensors are good because they produce much less noise (speckle), especially in long exposures, but operating a big sensor all the time would run down the battery. It would also cause the...

Mm SLR Camera

Capturing pictures of what you see in your telescope is one of the most rewarding and at the same time challenging tasks you can undertake in astronomy. In order to accomplish this you need a 35-mm SLR camera with a removable lens. A ring then is attached to the camera that will allow the camera to be mated to an adapter that directly threads onto the rear cell of the telescope in place of the visual back. The telescope then becomes the camera lens. This type of camera is the only type of camera that allows you to view directly through the light path rather than When buying a camera for astrophotography, buy as much quality as you can afford. If you buy a good camera, you will only have to do it once. Manual cameras are relatively inexpensive and have the advantage of not needing batteries that can die on you in extreme cold. Electric cameras operate much more smoothly and precisely. The quality of the lens of your camera is important since you will not always use it to image through...

Telephoto Moon

Even though the Moon is not ultimately the most rewarding object to photograph with a DSLR, it's a good first target. Put your camera on a sturdy tripod and attach a telephoto lens with a focal length of at least 200 and preferably 300 mm. Take aim at the Moon. Initial exposure settings are ISO 400, f 5.6, 1 125 second (crescent), 1 500 second (quarter moon), 1 1000 (gibbous), or 1 2000 (full) or simply take a spot meter reading of the illuminated face of the Moon. An averaging meter will overexpose the picture because of the dark background. If the camera has mirror lock (Canon) or exposure delay (Nikon), turn that feature on. Let the camera autofocus and take a picture using the self-timer or cable release. View the picture at maximum magnification on the LCD display and evaluate its sharpness. Switch to manual focus and try again, varying the focus slightly until you find the best setting. Also adjust the exposure for best results. If you have mirror lock or prefire, you can stop...

Digital SLRs

Digital single lens reflex cameras (DSLRs) are more capable and versatile than their compact cousins, generally offering higher resolution images, capable of taking time-exposure photographs, and offering a greater range of fine adjustments. The DSLR camera body is attached to the telescope using a T-mount adapter, effectively transforming the telescope into a large telephoto lens (Figure 2.38). Using prime focus, a telescope with a focal length of under 2,000 mm will project the entire half-degree-wide lunar disc onto the camera's CCD chip. Some DSLRs, such as the Olympus E-300 (of which this author has considerable experience), don't offer a live preview on their LCD view screens, so focusing needs to be performed by squinting through the camera's viewfinder. This may be easy enough for the Moon, but not so easy for dimmer objects. Here's where a full-aperture focusing mask comes in handy, using it to merge the image of a bright star to produce optimum focus. Figure 2.38. The...

Macro lenses

A macro lens is one whose aberrations are corrected for photographing small objects near the lens rather than distant objects. This does not imply a different lens design it's a subtle matter of adjusting the curvatures and separations of elements. Since the 1970s, many of the best macro lenses have had floating elements, elements whose separation changes as you focus. As a result, they are very sharp at infinity as well as close up. I have had excellent results photographing star fields with Sigma 90-mm and 105-mm macro lenses. At the other end of the scale, cheap zoom lenses often claim to be macro if they will focus on anything less than an arm's length away, even if they don't perform especially well at any distance or focal length.

CCD and CMOS sensors

Electronic image sensors work because light can displace electrons in silicon. Every incoming photon causes a valence electron to jump into the conduction band. In that state, the electron is free to move around, and the image sensor traps it in a capacitive cell. The number of electrons in the cell, and hence the voltage on it, is an accurate indication of how many photons arrived during the exposure. Modern sensors achieve a quantum efficiency near 100 , which means they capture an electron for nearly every photon. The difference between CCD and CMOS sensors has to do with how the electrons are read out. CCD stands for charge-coupled device, a circuit in which the electrons are shifted from cell to cell one by one until they arrive at the output (Figures 11.1, 11.2) then the voltage is amplified, digitized, and sent to the computer. The digital readout is not the electron count, of course, but is exactly proportional to it. CMOS sensors do not shift the electrons from cell to cell....

DSLR Software

A current favorite in this category is an inexpensive but very capable program, Nebulosity( 45). Not only does Nebulosity display the DSLR's images on the PC screen, making for easy focusing, it does many of the things any CCD software does control camera settings, take single exposures or a series of exposures, take and subtract dark frames, and even do some fairly sophisticated image processing. Nebulosity doesn't stop with DSLRs, either. It can be used to operate the Meade DSI, the Starlight Xpress, the SBIG CCD cameras, and a growing array of other deep sky and planetary imagers. Like other DSLR programs designed to allow the cameras to take long exposures, Nebulosity requires two connections from camera to PC. One cable delivers image data to the computer. The other connects to the camera's remote ( cable release ) interface to allow for and control long exposures. These cables and interface boxes are inexpensive and are available from Shoestring Astronomy Products (Appendix 1)....

Soiar Observing Techniques

That is a pity, because fhe Sun is a rewarding and endlessly fascinating subject which as a target tar amateurs has many odvantages. There's plenty of light so a large aperture isn't needed, nor is high magnification. It is the only star on which surface detail can be seen. Imaging is easy using the simplest of equipment. And of course, with the occasional exception of the Moonr it's the only astronomical body that is visible during the day.


Remember that you may have more than one telescope. Most main telescopes have a small telescope attached to their side to act as a finder, and in some cases there may be more than one. The objective of the finder must be blanked off (covered completely with an opaque screen), or equipped with a full-aperture filter before any soiar observing procedure is attempted with the main telescope The sunlight passing through a finder if it is not blanked off may be sufficient to cause burns or to damage parts of the telescope. Note also that most finders have cross-wire eyepieces to enable them to be used for aligning the main telescope onto an object. The focused image of the Sun is likely to melt or burn these cross-wires, so the finder should not be used for eyepiece projection unless a non-cross-wire eyepiece is put in place of the normal finder eyepiece (see the section on projection below for further details).


Stopping down just involves placing an opaque screen of cardboard, thin plywood or metal, which has a hole 75-100 mm across cut in it, over the telescope's objective (Fig. 2.5). (inly the light passing through the hole is then received by the telescope. For reflectors with a secondary mirror, the hole in the screen will need to be placed off-axis so that it is not obscured by the secondary mirror. Care should be taken to ensure thai the screen is firmly attached for if it were to fall off or blow away, the full aperture of the telescope would suddenly be gathering sunlight with possibly disastrous results to the observer or instrument. Owners of Cassegrain, Schmidt-Cassegrain and Maksutov telescopes, or any other design in which the primary mirror has a small focal ratio, need to take extra care whilst finding the Sun (NB See aiso the warning above about invalidation of some manufacturer's guarantees). The primary mirror of such telescopes can form an interna) image which has...

White Light

Limb darkening (Chapter 1) causes the edge of the solar disk to have an intensity in the visual region of only about 40 that of its centre. It is best observed using a magnification which enables the whole solar disk to be seen. This means xlOO or less for most eyepiece designs. Using a full aperture filter, limb darkening will normally then easily be seen without any other special adjustments being needed to the telescope. When projecting the solar image, a good shade will normally be required* or the scattered solar light from the surroundings will make the limb darkening difficult to distinguish.


The solar images produced by projection or through full aperture filters can be recorded by drawing or by using photographic CCD 17 digital or video cameras. Whatever device is used to record the solar image, following as many as possible of the procedures described in Chapter 2 to optimise that image will be very beneficial.


For many purposes photographic and digital cameras are interchangeable. Digital cameras have the advantage of producing images which may be loaded directly into a computer for image processing discussed later in this chapter), but generally have poorer angular resolution. They are quite sophisticated devices with autofocusing and au to expos tire usually as standard features. However, autofocusing may cause problems when using the camera on the telescope since the camera may attempt to focus on parts of the telescope structure rather than the image or be upset if polarisation is introduced into the image by the full aperture filter (Chapter 2). The same comment applies to autofocusing photographic cameras. Thus a relatively simple SLR photographic camera with manual focusing and exposure settings may be better for solar imaging and also for more conventional astronomical photography), Such cameras can often be picked up second hand very cheaply, and so having one dedicated for use on...

Video Cameras

Video cameras (Camcorders) can be used in place of the photographic, CCD or digital camera in any of the methods just outlined. A full aperture filter will be needed if the camera is pointed directly or through a telescope at the Sun, The S-VHS and Hi-8 formats offer better resolution than VHS or VHS C, but the resolution on a video image will still be poorer than that of a 35 mm camera image. If the video camera is used with its normal lens and full aperture filter, then the maximum optical zoom, and possibly supplementary lenses, will be needed to obtain a large enough image. Digital magnification can also be used, but since this simply expands the pixel sizes* no additional information is obtained.

Advanced Concepts Program

A program managed by NASA's Office of Space Access and Technology to identify and develop new, far-reaching concepts that may later be applied in advanced technology programs. It was set up to help enable unconventional ideas win consideration and possible acceptance within the NASA system. Among the areas that the Advanced Concepts Program is looking into are fusion-based space propulsion, optical computing, robotics, interplanetary navigation, materials and structures, ultra-lightweight large aperture optics, and innovative modular spacecraft architectural concepts.

Telescopes And Detectors 141 Telescopes

Where A is the wavelength of the observations, and 206,265 is the number of arcseconds in a radian. Thus, the human eye, with an effective aperture of 5 mm, has an angular resolution of 20 arcsec an 8-inch (20-cm) telescope can resolve double stars separated by 1 arcsec and the 200-inch (5-metre) Hale telescope at Mount Palomar has a diffraction limit of 0.02 arcsec at visual wavelengths, although atmospheric turbulence (seeing) prevents this resolution being attained in direct observations.

Astronomical image processing

MaxDSLR has a big brother (MaxIm DL, from the same manufacturer) and a head-on competitor (ImagesPlus, from, both of which offer even more features but are more complex to use. They work with astronomical CCD cameras as well as DSLRs and webcams. As an alternative to MaxDSLR I also use Nebulosity (from This is a quick and simple image processing package for DSLR users, similar in overall design to MaxDSLR but much lower priced. (The two make a good pair.) Like MaxDSLR, Nebulosity not only processes images, but also controls the camera in the field. It runs on the Macintosh as well as the PC.

Big Gun Number 1 Aperture and Telescope Choices

The best advice buy or build the largest aperture high quality telescope you can afford, equatorial or not. It is far better to forgo all the bells and whistles for light gathering power. Include as many of these bells and whistles as are useful to you, but only after aperture, as this should remain your priority. But also bear in mind that larger sizes will deliver high magnifications effectively on fewer nights, and are only of value if readily usable, practical, and suited to your own situation. Remember that, inch for inch, quality made Newtonian reflectors buy you much more than other varieties, and deliver outstanding performance. Personally, I tend to favor that design over most others anyway, and it has the wonderful feature of its eyepiece being located near the top of the tube and to the side, about the most accessible place it could be. I have always been amazed how this feature has been denigrated by some (perhaps by those popularizing other designs ). Except in cases of...

Barlow Lenses and Focal Reducers

Another variant on the Barlow theme is the zoom lens that introduces a movable negative element into the light path. By rotating a knob, the magnification of the telescope can be varied over a wide range allowing the user to work at different magnifications without changing eyepieces. Once you start handling expensive oculars with numb hands in freezing cold, you will quickly come to appreciate the value of a zoom eyepiece. In nearly all cases the Barlow lens or zoom lens slips into the drawtube of your focuser or visual back.

Aperture Ratio or Focal Ratio

The f-ratio Q is a positive number defined in the image space from an axial point at infinity in the object space. Denoting D the diameter of the parallel beam in the object space and efl the effective focal length - assumed positive - in the image space, Q efl D. In the Gaussian approximation, the ratio Q is two times the absolute value of the maximum aperture angle u'max,

Aperture Magnification and Field Diameter

The field diameter of a pair of binoculars is a numerical value expressed in degrees and fractions of a degree. It is directly related to magnification and objective lens diameter. For a given aperture, field diameter diminishes as magnification increases. As might be expected, it is easier to locate an object through binoculars with a wide field of view, because the area of sky represented is proportionately larger.

Raw vs compressed files

For that reason, astrophotographers normally set the camera to produce raw images which record exactly the bits recorded by the image sensor (or nearly so some in-camera corrections are performed before the raw image is saved). The term raw is not an abbreviation and need not be written in all capital letters it simply means uncooked (unprocessed). Filename extensions for raw images include .CRW and .CR2 (Canon Raw) and .NEF (Nikon Electronic Format). Adobe (the maker of Photoshop) has proposed a standard raw format called .DNG (Digital Negative) and has started distributing a free software tool to convert other raw formats into it.

New General Detector Controller

Between 1998 and 2008, a total of 30 FIERA and IRACE 18 systems will have been deployed at ESO's La Silla Paranal Observatory for optical and infrared detector systems respectively. Good performance and high reliability (the combined downtime of the FIERA hard- and software is of order 0.5 ) have been demonstrated in more than 10,000 nights of scientific operation. On June 30, 2005, the ESO Science Archive Facility held a total of 4.4 million raw files from the La Silla Paranal Observatory, of which nearly 100,000 were acquisition images, suggesting that a similar number of targets and fields having been observed.

Photographic Magnitude

Despite the fact that galaxies are extended objects, how do photographic magnitudes arise in galaxy catalogs Generally, galaxies on the plate must be compared by a certain method to the density caused by reference stars of known magnitude. Shapley and Ames used for their Survey of External Galaxies Brighter than the 13th Magnitude (1932) 20 a wide-angle lens. Even large and bright galaxies created an almost point-like image. In comparison with modern BT magnitudes, the Shapley-Ames magnitudes show an error of 0.5 mag, thus are not very reliable. Nevertheless they have been used in many popular catalogs and handbooks, e.g., Burnham's Celestial Handbook.

Digital film and camera software

DSLRs record images on flash memory cards, sometimes called digital film. Unlike real film, the choice of digital film doesn't affect the picture quality at all flash cards differ in capacity and speed, but they all record exactly the same data and are error-checked during writing and reading. Of course, there are good reasons not to ignore the software CD that comes with your camera. It contains drivers that you must install if you want to connect the camera to the computer, either for remote control or to download pictures. Also, there will be utilities to convert raw files to other formats and perform some basic manipulations. Even if you don't plan to use them, some astronomical software packages will require you to install these utilities so that DLLs (dynamic link libraries) supplied by the camera manufacturer will be present for their own software to use.

Darkframe subtraction

Typically, a few pixels are dead (black) all the time, and in long exposures, many others are hot, meaning they act as if light is reaching them when it isn't. As a result, the whole picture is covered with tiny, brightly colored specks. Beginning with the 2004 generation of DSLRs, hot pixels are much less of a problem than with earlier digital cameras. For non-critical work, you can often ignore them. Many newer DSLRs can do dark-frame subtraction for you. It's called longexposure noise reduction. On Nikons, this is an obvious menu setting on Canons, it is deep within the Custom Function menu.

Sensor size and multiplier zoom factor

Some high-end DSLRs have a sensor the size of a full 35-mm film frame (24 x 36 mm), but most DSLRs have sensors that are only two thirds that size, a format known as APS-C (about 15 x 23 mm). In between is the APS-H format of high-end Canons (19 x 29 mm). The rival Four Thirds (4 3) system, developed by Olympus and Kodak, uses digital sensors that are smaller yet, 13.5 x 18 mm.1 You shouldn't feel cheated if your sensor is smaller than full frame. Remember that full frame was arbitrary in the first place. The smaller sensor of a DSLR is a better match to a telescope eyepiece tube (32 mm inside diameter) and also brings out the best in 35-mm camera lenses that suffer aberrations or vignetting at the corners of a full-frame image. The sensor size is usually expressed as a focal length multiplier, zoom factor or crop factor that makes telephoto lenses act as if they were longer. For example, a 100-mm lens on a Canon Digital Rebel covers the same field as a 160-mm lens on 35-mm film, so...

Light Pollution and What to Do About It

Be aware, however, that these filters are most useful for astrophotogra-phy or digital imaging and are less effective if your primary imaging device is your own retina. Also, all filters block light, dimming the image you see so small-aperture telescopes will suffer most from this side effect. Write your local city government and encourage officials to install low-pressure, downward-facing sodium lamps. These lights have a yellowish glow and are highly energy efficient. You can get many good ideas on how to reduce light pollution from the International Dark Sky Association (find more at www. ).

Summary of the Options

If imaging of the smaller deep-sky objects, such as planetary nebulae and globular clusters, is to be attempted, we are more in a high-resolution regime, as with planets, best results requiring large apertures and very heavy and stable telescopes and mountings, and again a permanent site becomes a necessity. A portable telescope, even on an excellent tripod, can never be as stable as one on a properly-built permanent support. It is not totally necessary to have an observatory structure around a permanent telescope site, and this possibility will be dealt with in Chapter 3. For our purposes, an observatory is any fixed observing site, whether or not walled or roofed-in any way.

Telescopic Observations

Dark markings on the disk were reported by F. Fontana in 1645, but he was using a small-aperture, long-focus refractor, and there is no doubt that his 'markings' on Venus were illusory. In 1727 F. Bianchini, from Rome, went so far as to produce a map of the surface, and even gave names to the features he believed that he had recorded - such as 'the Royal Sea of King John', 'the Sea of Prince Constantine' and 'the Strait of Vasco da Gama'. Again these markings were illusory Bianchini's telescope was of small aperture, and as the focal length was about 20 m it must have been very awkward to use.

No reciprocity failure

Figure 2.3 shows the estimated long-exposure performance of an old-technology black-and-white film, a modern color film, and a DSLR image sensor, based on my measurements. The advantage of the DSLR is obvious. Astronomical CCD cameras have the same advantage. A practical consequence is that we no longer need super-fast lenses. With film, if you gather twice as much light, you need less than half as much exposure, so film astrophotographers were willing to compromise on sharpness to use f 2.8 and f 1.8 lenses. It was often the only way to get a picture of a faint object. With DSLRs, f 4 is almost always fast enough. You can either use an f 2.8 lens stopped down, for greater sharpness, or save money and weight by choosing an f 4 lens in the first place.

Finding Celestial Objects

Many observers report some degree of difficulty finding celestial objects when they begin using an astronomical CCD or DSLR camera. The skills needed to find objects for imaging are no different than those needed for visual finding the difference lies entirely in the accuracy required. While pointing within V20 is adequate for most visual observers, digital imaging is most efficient when you can accurately point the telescope within a few minutes of arc pointing errors of V20 are frustrating, if not unacceptable. Big Finders. The finders that come as standard equipment on many telescopes provide too little light grasp and magnification to center deep-sky objects accurately. A large-aperture finder telescope allows the observer to see and center fairly faint objects well enough that a flip-mirror system may not be needed. Many observers own an old 60-mm or 80-mm refractor these are obvious candidates to become auxiliary high-power finders. Depending on the size of the telescope, a...

Limitations Imposed by Aperture

Because of the obstruction of light by the secondary mirror, the effective aperture for a 90-mm Maksutov is 84 mm. Since there is additional light lost by two reflecting surfaces, the limiting magnitude for these telescopes is the same or slightly less than that of the 80-mm refractor.

Nebulae are blue or pink not red

But DSLRs see nebulae as blue or pinkish. There are two reasons for this. First, DSLRs include an infrared-blocking filter that cuts sensitivity to hydrogen-alpha. Second, and equally important, DSLRs respond to hydrogen-beta and oxygen-III emissions, both near 500 nm, much better than color film does.4 And some nebulae are actually brighter at these wavelengths than at hydrogen-alpha. So the lack of brilliant coloration doesn't mean that the DSLR can't see nebulae. DSLRs can be modified to make them supersensitive to hydrogen-alpha, like an astronomical CCD, better than any film. The modification consists of replacing the infrared filter with one that transmits longer wavelengths, or even removing it altogether. For more about this, see p. 133. Canon has marketed one such camera, the EOS 20Da. In the meantime, suffice it to say that unmodified DSLRs record hydrogen nebulae better than many astrophotographers realize. Faint hydrogen nebulae can be and have been photographed with...

Shutter speed and aperture

To set the aperture, some cameras have a second thumbwheel, and others have you turn the one and only thumbwheel while holding down the + -button. Note that on Canon lenses there is no aperture ring on the lens you can only set the aperture by electronic control from within the camera. Most Nikon lenses have an aperture ring, for compatibility with older manual cameras, but with a DSLR, you should set the aperture ring on the lens to the smallest stop (highest number) and control the aperture electronically.

Physical Description PST

The filter used for hydrogen alpha is called a Fabry-Perot etalon that isolates light at 6563 A. Its tolerance is quoted at 1A - essential for viewing both limb prominences and disc detail. So, depending on the exact position of the filtertuning knob, a typical range for the light to pass through is 6562.5-6563.5 A. Unlike other similar products manufactured by Coronado, the etalon is housed nearer the eyepiece. This is a slight disadvantage, compared to the MaxScope 40, as it reduces the effective aperture of the PST to about 30 mm. However, this change was undertaken to reduce the cost.

Cameras and Support Equipment

T-adapters, T-rings and tele-extenders do not require a great deal of care because they are simply empty tubes or rings. Still they can collect dust and once they are integrated with your camera or CCD, they can scatter that dust on eyepieces and camera innards. Not only must your lenses be clean, but also so must anything that potentially comes in contact or close proximity to them. You don't have to be as formal about cleaning such non-optical components. Instead of using your supply of compressed air, just blow in the tube to get the dust loose.

Do you want an automatic dark frame

Most newer DSLRs (but not the original Digital Rebel 300D) will do this for you if you let them. Simply enable long-exposure noise reduction (a menu setting on the camera). Then, after you take your picture, the camera will record a dark frame with the shutter closed, perform the subtraction, and store the corrected image on the memory card. Voila - no hot pixels.

A miniSpacelab mission 117

During STS-32, this 'L-cubed' instrument was used by crew members to take repeat photographs of a geographical feature every 15 seconds the data was then fed into an onboard computer, which calculated two possible sets of latitudinal and longitudinal coordinates. The crew, by knowing whether the target was 'north' or 'south' of their flight path, could then determine which set was correct. The instrument, which utilised a modified Hasselblad large-format camera with a wide-angle lens, proved extremely successful.

Tripping the shutter without shaking the telescope

Obviously, you can't just press the button with your finger the telescope would shake terribly. Nor do DSLRs take conventional mechanical cable releases. So what do you do Nikon makes an electrical cable release for the D70s and D80, but for most Nikon DSLRs, your best bet is the infrared remote control. Set the camera to use the remote control, and Bulb changes to - - on the display. That means, Press the button (on the remote control) once to open the shutter and once again to close it.

Getting Familiar with a Webcam

If you have never used a webcam before, it is essential to spend a few days playing with it and the manufacturer's software indoors with the webcam's normal lens attached. Get to know how to use the webcam in manual mode before you try connecting it to the telescope, i.e., untick the auto box (see diagrams). In passing, it is worth mentioning that the tiny webcam lenses, supplied with commercial units, usually have a crude infrared blocking filter, in the form of a coating or a plastic strip, attached to the rear lens. Once this lens is removed, the full sensitivity of the CCD chip, which reaches much further into the infrared (and a bit further into the UV) than the human eye will be revealed. While more sensitivity to light may seem a desirable feature, it does mean that when planets are low down the color dispersion will be considerable. Thus, many amateurs purchase an inexpensive UV-IR blocking

Nonreflective coatings

When light passes through a piece of glass, approximately 4 of the incident intensity is reflected at each surface. In all, a total of 7.7 of the incident light is reflected. Repeated reflections at the surfaces of composite photographic lenses may generate a significant amount of unwanted stray light in cameras and other such equipment.

Atmospheric structure not affected by magnetic fields

Athay and White (1979), in contrast, found that the C IV k 1,548 line intensities, observed by OSO-8 with an effective aperture of 2 x 20 , show relatively frequent periodic oscillations in the 3- to 5-min range. The periodic oscillations have a short coherence length and a tendency to be mixed with prominent aperiodic fluctuations. Athay and White propose that this mixing prevented other studies from uncovering these periodic variations. They interpret the much more frequent low-amplitude aperiodic intensity fluctuations as sound waves whose periodicity and coherence are destroyed by the variable transit time through an irregularly structured chromosphere (see the review by Deubner, 1994).

Refractor as the Main Imaaina Telescope

After imaging for maybe 6 months using the 11 GPS and Hyperstar, I felt that maybe I had made the wrong decision. The 11 GPS was certainly a beautiful instrument for observing, but I was having second thoughts about its perfection as an imager. I outlined the problems encountered with the Hyperstar system in Chapter1, but even if you were eyepiece imaging at larger f-numbers, you would still have to make sure your collimation was spot on for the best images. Collimation is something you don't need to think about in a high quality refractor. Now although it is relatively quick and easy to collimate a SCT, it is still an unnecessary worry to consider every time you want to image. In the reflector's favour, you really don't need to worry about chromatic aberration with a good quality SCT, and your stars will always end up looking good (provided your collimation is good ). In maybe a further 6 months or so I decided that the advantage provided by the bigger aperture really made the...

Recommended Accessories

As described in Chapter 9 an additional set of color filters for planetary observations provides higher contrast in certain aspects of their images. A 12.5-mm eyepiece with an illuminated crossline reticle is useful for some types of visual observations and for tracking long exposure film photography. A piggyback mounting bracket for a camera equipped with a telephoto lens is necessary for some digital and film photography. An electronic stopwatch is essential for lunar occultation measurements, timing eclipses and transits of Jupiter's moons and timing the transit of Jupiter's red spot. A red flashlight aids reading camera settings and recording data.

Two New Ccd Systems Since 2002

We chose 2D detector CCDs instead of CMOS image sensors. The main advantage of a CCD is its high quality. It is fabricated using a specialized process with optimized photodetectors, very low noise, and very good uniformity. The photodetectors have high QE (Quantum Efficiency) and low dark current. No noise is introduced during charge transfer. The drawback of CCDs include they can not be integrated with other analog or digital circuits such as clocks generation, control and A D conversion they have high power consumption because the array is switching continuously at high speed they have limited frame rate, especially for large sensors due to increased transfer speed while maintaining acceptable transfer efficiency. Note that CCD readout is destructive the pixel charge signal can only be readout once. Reading discharges the capacitor and eliminates the data. CMOS image sensors, however, generally suffer from lower dynamic range than CCDs due to their high read noise and...

NGC 869884 The Sword Handle Double Cluster

Although the Sword Handle Double Cluster (Figure 7.6) certainly qualifies as a supreme binocular object, it is so striking and successful even with large apertures in all locations that it can certainly justify its position on this list. Use the lowest power available in an effort to fit as much as possible of both clusters in the field of view at once. It is an amazing sight, and makes wonderful direct viewing with many star colors apparent, even without any kind of high-tech assistance. In the days when I had my 12--inch reflector, this was one of my favorite deep space objects, and in many ways it is most impressive at these moderate apertures, with the lower powers they allow, together with significantly higher light grasp than their smaller cousins. Intensification will bring out more stars, particularly since such a significant proportion of them are red supergiants. However, the video frames and my

Digital Imaging A Useful Cybersketching Tool

One potent method of cybersketching, particularly applicable to lunar and solar observations, is to use a live or almost-live digital image taken with a digicam, DSLR, webcam, or astronomical CCD device as the basis for an observational drawing. This kind of sketching technique is a 'simultaneous cybersketch' - an electronic drawing made with the aid of a simultaneously displayed digital photographic image that is used either as a reference and or as a template. Alternatively, it may be a traditional pencil sketch made using a low-contrast printed digital image template - a 'cybertemplate,' if you will - and these kinds of observational drawing might be termed 'digitally assisted' sketches. The techniques involved in these cybersketching methods are discussed in more detail later.

Imaging and Processing

Focusing is the first critical step for any imaging session. To avoid focus shifting caused by the main mirror of SCTs, the mirror should be locked. First I calibrate my go-to mount and use a bright star to focus the D-SLR. Visual focusing is easier when using the 2.5x angle viewer. A Hartmann mask or two parallel tapes across the lens improve the judging of the best focus. After determining the best focus it is essential to prove the focus by taking a test image of say 30 seconds and then checking it on the PC. At the optimum focus, sharp spikes and interference patterns on bright stars can be seen from the tapes. The freeware DSLRFOCUS helps with this procedure. Then the scope can be slewed to the desired object and the imaging can begin. Fast lenses should be stopped down one or two steps after focusing. During the night, as the temperature is typically dropping, a refocusing should be considered every one to two hours. For processing large raw files, ImagesPlus image processing...

Technical Aspects on Observing Galaxies

OK, let's talk a little about aperture-fever. Independent of the telescope size, you will always find objects looking similar to those observed in a binocular. Sure, it is a benefit of a large aperture to delve deeply into the structure of bright galaxies (see, e.g., the observations of Ron Buta 103 ). But under the right conditions even a small telescope can discern considerable detail. It can be quite fascinating to discover a certain Messier or even NGC galaxy in a small instrument. And sometimes, in case of large, low surface brightness galaxies, a small aperture can be even better There are challenging cases for every size and no serious visual observer would joke about small telescopes. It needs the same (or even more) degree of experience and observing technique to detect a 13-mag galaxy in a 4 in., than a 16-mag galaxy in a 20 in. In fact, there can be a minimum-aperture-fever too

Imaging Devices Detectors And Other Technology

The first, and still most widely used, astronomical telescope detector system is the human eye. With a relatively small aperture, and able to detect light only in the visible part of the spectrum (400-700 nm), the human eye has serious limitations. In this chapter so far we have described the techniques and telescopes that have enhanced our ability to see the universe. We now turn to the latest revolutionary detectors and other technologies that have improved that view. These include imaging devices such as charge-coupled devices, or CCDs, now commonly found in digital cameras, new radio-frequency detectors such as bolometers, bolometer arrays, and hot electron bolometer mixers, and techniques now enabled by such technological advances as mul-tiobject spectroscopy.

Intensity fluctuations twinkling

To the unaided eye, which has an aperture much smaller than the Fried parameter r0, the fluctuations in intensity are much more obvious than those of phase. On the other hand, for a telescope with diameter greater than r0, the intensity fluctuations have much less effect, since they are uncorrelated in the different isophase regions and therefore are averaged by the large aperture. The problem of twinkling, or scintillation, is therefore of rather marginal interest to astronomical observations, which are usually made with large-aperture instruments. However, for completeness, we

Naked Eye Tools Finderscopes

Naked-eye finders are sufficient only to locate bright targets. But they are helpful as the first step in the finding procedure, followed by the optical finderscope. The position of the finderscope depends on the telescope, but should be near the eyepiece. This is the upper end of the tube for a Newtonian (close to the telrad) or the lower end for a refractor or SCT. In case of a large aperture SCT it may be comfortable to install two finderscopes, located in opposite positions. For a larger Dobsonians a second finderscope makes sense too, put at the lower end of the tube, near the rocker box. To locate a difficult field, the star chart (on a nearby table) must be consulted several times. No problem, if the elevation is low and no stair is needed. But at high elevation, you must climb the ladder for each trial. Thus the lower finderscope saves time and make things more secure.

Prospects for Extremely Large Telescopes

A period of time the California universities merged their efforts with those of the U.S. and Canadian national observatories, in what is now termed a public-private partnership. Both of those organizations had carried out studies of their own for a Giant Segmented Mirror Telescope (GSMT) and a Very Large Optical Telescope (VLOT). The partnership was later renamed the Thirty Meter Telescope (TMT) project and Gary Sanders (Caltech) was appointed as the Project Manager. Due to conflict-of-interest issues, the U.S. National Observatory later withdrew its direct participation in the TMT project. Other large consortia also formed with the intention of building an ELT using one of the other technologies. The Giant Magellan Telescope (GMT) is a project to build a multiple mirror telescope with an effective aperture of 20 m using the borosilicate honeycomb technology and individual primaries of 8.4 m. Around the same time period, the European Southern Observatory consortium of nations began to...

Resolution Image Brightness and Contrast Perception

In our discussion of astronomical seeing, the theoretical limits of resolution as defined by the Rayleigh criterion do not hold if the two stars being observed are of unequal brightness (as with double stars of different visual magnitudes or different spectral type), nor does it apply thoroughly to resolution of detail on extended objects like planets. In actual practice, experienced observers with especially keen vision, under excellent seeing conditions, are able to resolve double stars of the same magnitude with angular separations below Rayleigh's threshold with a given aperture. This empirical resolution criterion, or Dawes's limit, denoted by Rd, was established long ago by visual observations of double stars, and is defined by Equation 3.10 as ranging from about 350x to 500x are necessary to see them to advantage. It is obvious that large apertures are mandatory for good image characteristics at these powers. Larger surface features may be detected with low to moderate...

Catadioptric Telescopes and Cameras

In this chapter we discuss various derivatives of the Schmidt type of telescope, including Schmidt-Cassegrain, Baker-Schmidt, and Bouwers-Maksutov systems. Each of these is a type of catadioptric telescope in which a full-aperture refracting element provides the aberration correction needed to get good imagery over a wide field. Given this definition, the classical Schmidt telescope is also of this type.

The Developing Telescope

Another famous observer during the era of the long lens telescopes was the Polish Johann Hevelius (1611-1687) who had his own observatory in Danzig, the first one in the world complete with a telescope. His wife Elisabeth made observations too. Hevelius' record-sized instrument was 150 ft. or 45 m long. Its complicated system of ropes and long rods reminded one of the rigging of a sailing boat and certainly required seaman's skills to handle With his telescopes Hevelius studied the surface of the Moon and drew fine maps of it. Our habit of speaking about the seas on the Moon goes back to Hevelius. We now know these to be depressions filled with solidified lava. The development in the eighteenth century of achromatic lens telescopes in which color fringes are greatly reduced ended the era of the long lens telescopes. Large diameter objective lens telescopes up to about a meter in diameter were built through the 1800s but another kind of telescope was developed that gradually came to...

Image scale in pixels

Unlike astronomical CCD camera users, DSLR astrophotographers do not often deal with single pixels because there are too many of them. Even a pinpoint star image usually occupies six or eight pixels on the sensor. This is a good thing because it means that star images are much larger than hot pixels.

Short exposure images speckle patterns

We shall conclude this chapter where we started it by looking again at the atmospheric degradation of a stellar image. Does the K41 model of turbulence give a good picture of the point spread function of a large-aperture telescope Although long-exposure images of point stars have long been recorded, and have been used in some ways to investigate this question, it becomes much more interesting when applied to instantaneous images which show the effect of a frozen statistical state of the atmosphere. This became possible with the development of image intensi-fiers having amplifications of the order of 106 and reasonable quantum efficiencies (about 10 ). The resulting speckle images, of which we showed an example in figure 5.1, are the basis of the technique of speckle interferometry, initially suggested and developed by Labeyrie (1970) and discussed in detail in chapter 6. We have already discussed (section 5.5.1) the frequency spectrum of fluctuations, which determines how short an...

Village Resources Centre VRC

In the areas of education, health, nutrition, weather, environment, agriculture and livelihoods to the rural population and to empower them to face the challenges. The VRC is a totally interactive VSAT (Very Small Aperture Terminal) based network. VRCs are being set up in association with grass root level organisations, who have a strong field presence and experience of mobilising communities to act for development with proven track record.

Visual Observations of the

The traditional method of viewing the Sun has been to project its image onto a white surface attached by rods to the eyepiece end of the telescope. This has been supplanted by the use of special full aperture filters placed in front of the objective lens. These filters, made either of glass or mylar film, have metallic coatings that block ultra violet radiation and transmit only 0.0001 of the Sun's light. They are safe and provide a more detailed view than projection. Maksutovs must be used with a full aperture filter. Because of the internal reflections in a small closed system, the Sun's heat can damage the optical system if the telescope is used for an extended period with the eyepiece projection method.

Vignetting and edgeoffield quality

As Astrophotography for the Amateur explains at length, few telescopes produce a sharp, fully illuminated image over an entire 35-mm film frame or even an entire DSLR sensor. The reason is that telescopes are designed to work with eyepieces, and with an eyepiece, what you want is maximum sharpness at the very center of the field. A more noticeable problem is vignetting, or lack of full illumination away from the center. An APS-C-size DSLR sensor is slightly larger, corner to corner, than the inside diameter of a standard eyepiece tube. Thus, to reduce vignetting, you should avoid working through a 14-inch eyepiece tube if possible switch to a 2-inch focuser or a direct T-adapter. But even then, a telescope with glare stops designed to work well with eyepieces will not fully illuminate the edges of the field. Vignetting can be corrected by image processing (p. 188), but I prefer to take a more optimistic approach. It's not that the image is small it's that the sensor is big. A DSLR...

Saqi Marius rtornarJ 96 fcrna Scorpius

Several reflection nebulae reside within the same gas clouds as emission nebulae, the Triftd nebula is a perfect example- The inner parts of the nebula are glowing with the tell-tale pink colour, indicative of the ionization process responsible for the emission, whereas further out from the centre, the edge material is definitely blue, thus signposting the scattering nature of the nebula. Visually, reflection nebulae are very faint objects having a low surface brightness, thus they are not easy targets. Most require large aperture telescopes with moderate magnification in order to be seen, but there are a few visible in binoculars and small telescopes. Mote that excellent seeing conditions are necessary and very dark skies.

Big Gun Number 3 Image Intensifiers

Magnetic Focused Image Intensifier

Thing of a problem when alternating regular and intensified viewing. Despite what you may have read, you should know also that averted viewing of many objects with image intensifiers will indeed reap considerable rewards. This is never more the case than when looking for dark lanes , and other aspects of contrast. I don't believe the eye changes its sensitivity to these things just because we are using an image intensifier The practical effect in light gathering (not resolution) is frequently comparable to doubling or even tripling your telescope's effective aperture, and remember, aperture is the thing Imagine being able to look directly into the eyepiece and seeing many well-known objects looking so recognizably close to their well-known portraits Additionally, as mentioned before, there are some recent advances in light filters especially for image intensifiers, which are designed to increase their effect still further. (See Chapter 3.)

Why you need another lens

You will have gathered that I think piggybacking is one of the best astronomical uses for a DSLR. But the kit lens that probably came with your DSLR is not very suitable for piggyback astrophotography. It has at least three disadvantages It is a zoom lens, and optical quality has been sacrificed in order to make zooming possible. It is plastic-bodied and not very sturdy the zoom mechanism and the autofocus mechanism are both likely to move during a long exposure. Fortunately, you have many alternatives, some of which are quite inexpensive. One is to buy your camera maker's 50-mm f 1.8 normal lens despite its low price, this is likely to be the sharpest lens they make, especially when stopped down to f 4. Another alternative is to use an inexpensive manual-focus tele-photo lens from the old days. There are several ways of doing this Nikon DSLRs take Nikon manual-focus lenses (though the autofocus and light meter don't work), and Canons accept several types of older lenses via adapters.

Major manufacturers Canon

Many astrophotographers have settled on the Canon Digital Rebel, XT, XTi (EOS 300D, 350D, and 400D) and their successors. These are low-priced, highperformance cameras. One reason Canon leads the market is that Canon is the only DSLR maker that has specifically addressed astrophotography, first with tutorials published in Japan1 and then, briefly, by marketing a special DSLR for astrophotography (the EOS 20Da). Also, because Canon SLR bodies are relatively compact, you can use other brands of lenses on them, including Nikon, Olympus OM, Leicaflex, Contax Yashica, and Pentax-Praktica M42 screw mount. For more about lens adapters, see p. 80. Of course, with an adapter, there is no autofocus, but with Canon DSLRs, you can use the exposure meter and aperture-priority auto exposure (useful for eclipses) with any lens or telescope. So far, there have been three generations of Canon DSLRs suitable for as-trophotography. The EOS 10D and Digital Rebel (300D) used the original Canon DIGIC image...

Big lens or small telescope

In my opinion and experience, good telephoto lenses perform even better. After all, they have more elements and more sophisticated optical designs. If two or three lens elements were enough, even with ED glass, that's how camera makers would build telephoto lenses. It isn't. The advantage of the telescope is its versatility. You can use it visually as well as photographically, and it may well come with a mount and drive of its own, whereas the telephoto lens would have to be piggybacked on an existing telescope. It may also accommodate a focal reducer, which telephoto lenses never do. There is certainly a place for both types of instruments in astrophotography.

South Equatorial Belt SEB

Southern hemisphere of Saturn, the SEBn is commonly slightly darker than the adjacent SEBs. Visual observers with different apertures regularly detect diffuse dark spots and dusky projections emanating from the northern border of the SEBn, extending into the EZs during many apparitions. Figure 4.3 is a good example of the kind of discrete phenomena sometimes visible along the SEBn neighboring the EZ when viewing conditions are above average in moderate apertures. Of course, atmospheric phenomena are normally easier to see with larger telescopes. Most dusky features in the SEBn or SEBs are short-lived and do not

Sharpness vignetting distortion and bokeh

Having said that, I should add that the situation with DSLRs is not quite the same as with film. High-speed film is itself very blurry light diffuses sideways through it, especially the light from bright stars. When you put a very sharp lens on a DSLR and this blurring is absent, the stars all look alike and you can no longer tell which ones are brighter. For that reason, less-than-perfect lenses are not always unwelcome with DSLRs. A small amount of uncorrected spherical or chromatic aberration, to put a faint halo around the brighter stars, is not necessarily a bad thing. What is most important is uniformity across the field. The stars near the edges should look like the stars near the center. All good lenses show a small amount of vignetting when used wide-open the alternative is to make a lens with inadequate glare stops. Vignetting can be corrected when the image is processed (p. 188), so it is not a fatal flaw. Another way to reduce vignetting is to close the lens down one or...

Cmos detector technology

Abstract An entry level overview of state-of-the-art CMOS detector technology is presented. Operating principles and system architecture are explained in comparison to the well-established CCD technology, followed by a discussion of important benefits of modern CMOS-based detector arrays. A number of unique CMOS features including different shutter modes and scanning concepts are described. In addition, sub-field stitching is presented as a technique for producing very large imagers. After a brief introduction to the concept of monolithic CMOS sensors, hybrid detectors technology is introduced. A comparison of noise reduction methods for CMOS hybrids is presented. The final sections review CMOS fabrication processes for monolithic and vertically integrated image sensors. Key words CMOS, image sensor, APS, active pixel sensor, focal plane array, hybrid, HgCdTe, InSb, CCD, three-dimensionally stacked circuits, vertical integration.

Observing Project 7C Catching Interlopers in the Darkness

The NEAT and LINEAR robotic telescopes have charted thousands of asteroids orbiting in the vicinity of Earth. In this project, we will use a simple 35-mm camera to demonstrate how NEAT and LINEAR work to expose potential trespassers in the near-Earth environment. You will also need your clock driven telescope and the longest telephoto lens in your bag. NEAT and LINEAR use computer databases to compare the images that they take on a rapid-fire basis against the known sky. Anything that does not belong there is instantly identified and astronomers then can use sequential images of the object to determine its path through the sky. We will use the telescope's clock drive and a camera with a telephoto to try and duplicate what NEAT and LINEAR do to much fainter magnitudes. Before going out, you will need to do some careful study and planning. NEAT and LINEAR have all the information they need in their computerized brains but you do not. You will want to use a star chart that shows the sky...

Huygensfresnel Principle

This statement suffices to account for the laws of reflection and refraction, and the approximately straightline propagation of light through large apertures, but it fails to account for diffraction, the deviations from exact straightline propagation of light. Fresnel extended Huygens' principle by assuming that the secondary wavelets interfere with one another according to the principle of superposition. His statement postulated that each unobstructed point on a wavefront is a source of spherical wavelets, and that the amplitude of the wave at any point ahead of the wavefront is the superposition of all of these wavelets. In adding these wavelets it is necessary to include the amplitude and phase of each wavelet. The Huygens-Fresnel principle was put on a firm theoretical basis by Kirchhoff and expressed as an integral derived from the wave equation. Details of the derivation of the Fresnel-Kirchhoff diffraction integral can be found in Born and Wolf (1980) or any intermediate optics...

Emerging Technologies

Without further limiting the pixel fill factor, monolithic architectures also require that addressing and signal processing circuitry be placed at the periphery of the array. In contrast, a three-dimensionally (3-D) stacked circuit construct, such as shown in Fig. 17, relieves many of the limitations inherent to monolithic structures. Active-pixel focal plane architectures are well suited for 3-D interconnection because signal integration, amplification, and readout can be in close proximity to the photodetection elements while still achieving 100 optical fill factor. The further capability to perform complex signal processing behind every pixel can dramatically reduce total image sensor power and bandwidth requirements. Vertically hybridized flip-chip imagers already offer independently optimized photodetector and readout multiplexer designs that can achieve scientific-grade image sensor performance 9 . However, these bump-bonded approaches are limited to two circuit layers, to large...

PSR Optically variable pulsars

Only a handful of pulsars are listed within the GCVS and all are extremely faint. As optical targets, these exotic objects cannot be recommended for casual examination or study. If considered for serious study, earnest amateurs will require large aperture telescopes augmented with sensitive instruments such as CCDs.

Which lenses fit which cameras Canon

In its long history, Canon has made two completely different kinds of SLRs, F (FD) and EOS. All the autofocus cameras, film and digital, belong to the EOS line, also referred to as AF (autofocus) or EF (electronic focus). The older FD-series manual-focus lenses do not fit EOS cameras at all, not even with an adapter. Canon also makes a few EF-S lenses ( electronic focus, smaller ) that fit only the newer DSLRs. They have an EOS-type mount that protrudes slightly farther into the camera body. If all you need is a T-ring, the situation is simple. Any T-ring marked Canon EOS, Canon AF, or Canon EF is the right kind for an EOS camera. The other kind, Canon F, FD, or FL, will not fit on the DSLR at all. Beware of Canon lenses made by Sigma and other third-party manufacturers in the early days of the EOS system. Sigma and some competitors reverse-engineered the EOS aperture system and got it slightly wrong, so the older lenses will not stop down to the selected aperture on a modern DSLR....

Difficulties In Observing Mars

Because of the limitation set by seeing, telescopes with very large apertures do not show any greater detail of the Martian surface than do smaller instruments. According to R. S. Richardson, the planet looks as if all the color has been washed out of it when viewed with the full aperture of the 100-inch reflector telescope of the Mount Wilson Observatory, California. The sharpness of the image, he goes on to say, can be considerably improved by diaphragming down, or partially covering, the secondary mirror.

High Resolution CCD Imaging

Using telescopes as small as 75mm aperture, amateur astronomers are now producing stunning images rivaling those of professional observatories of just a few years ago. The public has been fascinated by the dramatic and colorful highresolution images taken by the Hubble Space Telescope, yet recent amateur astronomical images have been no less inspiring. Over the last few years the art of amateur imaging has made a quantum leap forward with film-format-sized CCDs, professional-quality large-aperture telescopes and sophisticated image-processing techniques all arriving on the scene. Just as important, amateur astronomers have learned how to master them.

Objective Lens Assemblies

Some Common Eyepieces

Large aperture astronomical binoculars have objectives of relatively small focal ratio, often as small as f 5, and sometimes less. An achromatic doublet of 100-mm aperture with a focal ratio of f 5 will have significant chromatic aberration, especially off-axis, no matter which glasses are used. This can be particularly obtrusive on bright objects, such as the Moon or the naked-eye planets. Even a fluorite apoc-hromat of this aperture and focal ratio will show off-axis false color on these objects.

Why Is Seeing Control So Important

With the goal of extracting the highest resolution possible in our CCD images, seeing plays a much bigger part than is at first realized. Longer exposures do not mean you can detect an object if the seeing is poor. At the 2004 Riverside Telescope Makers Expo, Jim McGaha, an advanced CCD imager specializing in Near Earth Object (NEO) detection, gave a talk centered on detecting objects fainter than 20th magnitude. Using information presented in his talk, Table 8.1 reveals how a much fainter star can be detected with any given aperture of telescope as the seeing improves.

The viewfinder eyepiece

The eyepiece on a DSLR is commonly out of focus. Most DSLRs have an adjustment called the eyepiece diopter (Figure 8.1) which you are expected to adjust to suit your eyes. This is rarely done, because for daytime photography with an autofocus camera, it doesn't matter. To someone who always uses autofocus, the viewfinder is just for sighting, not for focusing, and the image in it need not be sharp. Half an hour of doing this will greatly build your skill. Before long, you should be able to focus your daytime pictures better than the camera's autofocus mechanism does. Try it.

Star Atlases and Catalogues

Other much more detailed atlases have appeared in recent years, such as Uranometria 2000.0 and The Millennium Star Atlas. Plotting hundreds of thousands (or more ) stars and deep-sky objects, they were published partly in response to the growing use of truly huge, large-aperture Dobsonian-type reflectors by amateur astronomers today. In practice, these massive volumes are often unwieldy and confusing to use at the eyepiece at night. For the purposes of most double star observers, they are definitely overkill.

Viewfinder magnification

The magnification of a viewfinder is a confusing quantity because DSLRs are still rated by an obsolete standard for 35-mm film cameras. For example, the nominal magnification of the Canon XTi viewfinder is x 0.7. This means that the camera and viewfinder would work like a x 0.7 telescope if you put a 50-mm lens on it - which is not the standard lens for a DSLR.

Replacement and Resiting

In 1989 the 10 in telescope returned on its new mounting which proved to be a marked improvement on its predecessor. The C8 was sold and replaced with a Vixen SP102F fluorite refractor on a tripod mounting which allowed it to be kept indoors and used as a portable telescope and also, with the aid of an Inconel full-aperture filter, as a solar telescope. Later an H-alpha filter was purchased which allowed observations of flares and prominences.

Imaging with very high resolution using multimirror telescopes

Recent years have seen very large aperture telescopes constructed by piecing together smaller mirrors and carefully mounting them on a frame so that the individual images interfere constructively at the focus. This way the two multimirror Keck telescopes on Mauna Kea are constructed, each from 36 hexagonally shaped mirrors which together form a paraboloidal mirror about 10 m in diameter. The frame is constructed very rigidly, but since each segment weighs half a ton, it still distorts significantly when the telescope is pointed, so that the mirror positions have to be actively corrected to compensate for the small movements. Then, together with adaptive optics correction for atmospheric turbulence, diffraction-limited images are obtained since, for a small enough field of view, the off-axis aberrations of the paraboloidal mirror are insignificant. However, the maximum aperture which can be operated this way is expected to be of the order of 100 m, the size of the Overwhelmingly Large...

Features Of Interest

1 EQUULEI 5 A 5th-magnitude star with a 7th-magnitude companion visible through small telescopes. On some maps, this star is also labeled as Epsilon (e) Equulei. The brighter star is, in fact, a true binary, having a faint second companion with an orbital period of 100 years. The stars are too close to be separated with a small aperture.

Knifeedge and Ronchi focusing In theory

The trouble with Ronchi or knife-edge focusing is that you can't do it with your DSLR in place. You must remove the DSLR and substitute a film camera body with no film in it, then run the knife edge across the film plane or put the grating there. The two camera bodies must match perfectly - but a film SLR body is unlikely to be a perfect match to a filter-modified DSLR because changing the filter changes the focal plane. Many astrophotographers feel that the Stiletto or an equivalent device is the gold standard of focusing. I don't use one myself for two reasons. First, anything that requires me to swap camera bodies will increase the risk of getting dust on the sensor. Second, it is easy to sample the actual DSLR image electronically, and that's what I'd rather use for my final focusing.

The rules have changed

The author's DSLR astrophotography setup. Meade LX200 telescope with piggyback autoguider (Figure 9.9), 8 x 50 finderscope, Canon 300-mm f 4 lens, and Canon XTi (400D) camera, mounted equatorially on a permanent pier in the back yard. Figure 9.3. The author's DSLR astrophotography setup. Meade LX200 telescope with piggyback autoguider (Figure 9.9), 8 x 50 finderscope, Canon 300-mm f 4 lens, and Canon XTi (400D) camera, mounted equatorially on a permanent pier in the back yard.

Capabilities and Limitations

As a comparison with the PST, there is necessarily no much improvement in the viewing of prominences, but the MaxScope 40 shows any sunspots (most of them that are visible in white light ) and shows the cell structure of the Sun quite clearly. Whilst some of this is due to the larger effective aperture, the lower bandpass of 0.7 A also helps. Figures 4.11 and 4.12 show the Sun on a day of high activity near the upper right limb of the disc. However, its effective aperture is more than the PST and its weight of only 3 lb (same as the PST) means that it has the same portability. Perhaps the greater price may require special insurance arrangements when traveling by car or air.

Semaphores for optical telegraphy

For thousands of years the use of light signals for sending messages over long distances was limited by the performance of the human eye. By the 13th century it was known that a glass lens in front of an eye could correct for long sight, but it was not until the beginning of the 17th century that it was discovered that two different lenses mounted at opposite ends of a tube could make distant objects appear larger and dim objects more visible. Such slow progress in optics is not surprising because the expounding of scientific theories in Europe was apt to lead to arrest, torture and death, even at the start of the 17th century. However, in the 1660s Louis XIV gave one of his sunny smiles to the Academie des Sciences in Paris, and in the same decade the Royal Society in London obtained its charter from King Charles II. One of the first officers of the Royal Society was Robert Hooke, who made important contributions in many fields of science. He described the use of telescopes in...

Detection of ultrahighenergy cosmic rays

Ground facilities, including the large Auger array in Argentina, observe the extensive air showers from the ground, but they are limited by the local horizon. A space detector for ultra-high-energy cosmic rays looking down from low Earth orbit could witness the events around a much larger swath. It would need a large-aperture telescope and sensitive light detectors in

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