Big Gun Number 3 Image Intensifiers

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The third and most important weapon in my city viewing arsenal, after the telescope itself, was the purchase of a modern third generation image intensifier, especially made for astronomy (the remarkable I3 Piece by Collins Electro Optics). The beauty of the Collins device is that you use it just as you would a conventional eyepiece. Image intensifiers require no image processing, monitors or separate controls.

Image intensifiers per se are hardly new to astronomy, and have been written about quite regularly since the late 1970s; actual applications in real time observing have been only marginally discussed in publications for amateur observers. New generations make them more valid than ever, and they are far from being fully recognized for what they can offer. You will soon realize that they represent a significant focus of this book. While expensive to be sure, I must stress that image intensifiers are the single most significant accessory I know of for our dubious surroundings. They will cost you less than most good CCD equipment with all its trappings.

The CCD revolution that has taken place has resulted in the intensifier taking something of a back seat to the pursuit of acquiring of highly resolved astronomical images. Nevertheless, the central theme of this book remains focused on real time observing. I still chuckle at an advertisement which actually boasted of the beautiful images that could be recorded by a CCD camera attached to the owner's telescope while he spent time inside watching TV with his family! Another proclaimed the wonders of recording near-limitless numbers of deep space objects, while our supposed astronomer was able to sleep peacefully through the night! Outside of comet, asteroid and supernova hunting, doesn't this approach miss the whole point of amateur astronomy in the first place?

Even though it is possible to download amazing CCD images off the Internet, none of this produces the joy of seeing these objects with one's own eyes. While image intensifiers do not work on everything, their effects are so significant on so many subjects that they bring much of what we have lost in the suburbs back into visibility. Where they do not work, it is typically because an object emits its predominant spectrum around a wavelength less favorable to the intensifier, negating its value. This might even result in negative results, since skyglow will also be increased relative to the object. Disappointment likely will result with their use on most reflection nebulae, objects that usually reflect light from the blue end of the spectrum, the portion in which image intensifiers are least responsive.

One of the primary differences between an image intensifier's range and that of the eye is that the intensifier responds to a wider spectrum, and is strongly biased towards red and infrared, including the celebrated Oxygen III emission line of 496.32 nm. When the intensifier is able to gather light concentrations nearest to its highest response, results are at their most startling, and can reveal an object in a dramatic way. The most advanced intensifiers available to the public are designed to minimize "noise", and thus are better suited to enhance contrast between object and sky, particularly in conditions that might not have worked so well with earlier designs. One should still be prepared for some slight noise and "snow" in the image, and though these devices achieve decent focus, star points become noticeably larger disks with increasing magnitudes.

Because of known information on the makeup of the light coming from any given object, one should theoretically be able to predict how effective the intensification will be. In reality, part of the fascination is that one never knows exactly how well it will work in practice, and it is quite possible to be completely bowled over when least expecting it! I will never forget my first view of M82 with intensification. With such a large and bright galaxy of its particular spectral makeup, I knew it would be good. In practice, though, I was stunned by all the tangled detail and brightness suddenly visible to me, where only a formless smudge had been before. The range of light, shading and dark veins was truly astounding, regardless of any expectation I had.

The image seen through these devices is also right side up, as in terrestrial telescopes. Seen as an image on a phosphor screen, it is monochrome green (Figure 2.1). At first this might seem to be a distraction, but it is amazing how quickly the eye gets used to it, and effectively interprets what it sees as black and white; even a partially dark adapted eye reduces awareness of color still further. Green pictures would be a distraction (although striking!), because in the context of the page, and in normal lighting conditions, they will only be seen as green! For this reason, all intensified real time images are reproduced here black-and-white. (Those by W.J. Collins, digital camera short time exposures, are in color, to convey the initial live impression through the telescope.) The color of the intensifier image is not just a quirk that we have to live with; it is selected as the best frequency for the eye in dark conditions. The image, of course, includes all frequencies, even those not normally visible, or marginally so. This can give us a significant boost in sensitivity to regions of the spectrum that have not been gobbled up by pollution and skyglow.

All of the above might lead you to believe that the view through such devices would seem completely artificial, and far detached from the spirit of real time viewing. Surprisingly, this is not the case, and intensified viewing seems as natural and real as any other, once you get used to the immediate differences. Only a limited amount of dark adaptation for the eye is needed, a nice by-product, although this can be some-

Magnetic Focused Image Intensifier

Figure 2.1. Example of real time image. M16 in Serpens, intensified image.

Courtesy W.J. Collins.

Figure 2.1. Example of real time image. M16 in Serpens, intensified image.

Courtesy W.J. Collins.

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.)

You will also probably hear the argument that it is just a matter of time before technology will outdate any intensifier equipment you buy and its value will drop like a stone; an important issue considering the costs involved. I don't believe this is an accurate assessment. This sophisticated technology is not like the latest thing in consumer electronics or automobiles. It is not like a new TV or DVD player. Actually, there is already a fourth generation intensifier tube in existence, though its slight benefits for astronomical use would probably not be worth the much greater additional cost to most people. You will see from any research you undertake that earlier generations of intensifiers are still very much in existence, and even now, good quality examples for our purposes are not exactly cheap. So it is fair to say that the best technology available today will likely still be giving good results years from now with just a little care, and that further developments will not automatically reduce today's equipment to obsolescence.

Collins Electro Optics presently has no international distributors, so check with them for specifics in your own situation, as certain export restrictions exist at the time of this writing. However, there are other highly viable options available, though none so ideal as the Collins. Even a used unit might fit the bill. I am not sure if it would be possible at this date to find a Collins I3 on the secondhand market, but you may be able to find another make from an earlier time. In the early 1980s, a company out of New Jersey, by the name of Electrophysics Corporation, offered complete eyepiece/

intensifiers much like the I3 in concept, only far bulkier. Another company, by the name of Varo, popularly marketed intensifiers which were commercially adapted for use with telescopes under the trade name Noctron. It may still be possible to locate one of these older units, and even a later and upgraded model, in the used marketplace. Perhaps one might provide worthwhile results. (I do stress that these older makes are earlier generations, and you should not expect equivalent performance of the I3. The signal-to-noise ratio of the I3's Generation III tube is many times superior to what preceded it, not to mention its improved spectral response. This becomes ever more important when searching out faint objects, and particularly in our worsening suburban sky conditions.)

Meanwhile, Electrophysics Corporation is still alive and well (see Appendix A), offering a wide range of intensifier products (Generations II through IV) that can probably be adapted to astronomical use with a little ingenuity. Noctron products (with second and third generation tubes) are now marketed by Aspect Technology and Equipment, inc. in Texas, but are manufactured as complete night vision scopes of very low magnifications. Some of these products also may likely lend themselves well to adaptation to astronomical use. There are many other suppliers of image intensifiers in Europe as well, some of them offering Generation III intensifiers. So there is a wide choice available. Bear in mind that the more advanced the generation, the higher the cost is likely to be. I do not know which of these companies would be willing to work with a prospective purchaser of components only, though I believe most will. Regrettably, to my knowledge, no other intensifier product today is ready to go as a real time astronomical device. Apparently, only Collins provides such a thing today, in 2003, if you should be so fortunate to acquire one. It is a beautiful unit indeed, featuring a ready-to-go combination of premium intensifier technology, specialized integral eyepiece component, and 1--inch or 2-inch adapter. There is also a line of high grade accessories. Apparently only one company at the present time is willing to take the sizeable business risk of presenting such equipment, long available to professional astronomers, to the amateur. Such risk taking requires a considerable vision of what possibilities this technology can offer. Bill Collins has carved out for himself a unique place amongst those who have helped propel amateur astronomy to new horizons; he deserves recognition as today's lone pioneer, and has certainly had no help in many seemingly likely places. Philip S. Harringtons' Star Ware (published by John Wiley), touted as the ultimate guide to all things for the amateur astronomer, doesn't even mention image intensifiers. Collins' products have even met with outright hostility in some amateur astronomers' circles. (For some manufactures and distributors in the USA and Europe, technical information on the Collins system, and third generation image intensifiers, see Appendix.)

Intensifiers project a tiny image onto an integral concave "screen", which needs to be magnified and rendered flat. The eyepiece component made by TeleVue for the Collins I3 is designed to produce a flat image and magnify it to the specifications, something like a sophisticated magnifying glass. In the case of the I3, the units are supplied producing either the eyepiece equivalent of 25 mm or 15 mm focal lengths. The two versions are used like an eyepiece of similar focal lengths. The unit can readily be attached to a Barlow lens for different magnifications; more on that later. Although their fields of view are substantially narrower than today's new breeds of multiple lens eyepieces, they are certainly more than adequate for our purposes. In adapting intensifiers other than the I3, it ought to be possible to select an eye lens to produce a usable image across at least a portion of the field, but experimentation is the keyword. The only other issue is providing the unit with a 1--inch or 2-inch tube adapter to allow it to fit your focuser like any other eyepiece.

As with all astronomy, stray light is also an issue for image intensifiers. Bad as any reflected light will be on contrast in normal circumstances, when this light falls into an intensifier, the results are disastrous. All such light will be amplified tens of thousands of times, and what may seem insignificant to general viewing becomes like the light of day in an intensifier. Such events can also damage the unit itself if they are bright enough. Be sure to baffle all potential stray light sources from entering the optical path, and above all, out of the image intensifier.

If you decide to pursue image intensified astronomy, then at the very least buy the best intensifier you can afford. I feel strongly that you will find that in the suburban sky conditions we face, this tool will become second only to the telescope itself. Still more innovations are available to help crack the problems we face, but none of them to date (except filters - on certain subjects) can enable the user to look directly at so many deep space objects, and experience them so effectively through the telescope, live, and in real time. Although clearly at a disadvantage, the reader-observer without access to such equipment, or even a good light filter, need not despair to the point of thinking all is lost. If he has easy access to a location significantly better than mine, he can take much of the information in these pages, and apply it to unaided real time viewing, with significantly more modest equipment. He can still expect a decent show. (See also Appendix A for more information and specifics.)

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