Astro Webcam Manufacturers

In the last few years a number of custom companies have sprung up in response to the need for affordable CCD imaging for those amateur astronomers with a tight budget. In many cases the products offered have simply been modified webcams, altered by a few wiring changes such that long, if noisy, exposures are possible, making webcams suitable for deep sky imaging. By stacking hundreds of frames, the noise has been reduced to acceptable levels for exposures of 30 seconds or so (often the unguided technical limit of the telescope's drive). Other webcam-modified products have included air-cooled and Peltier-cooled webcams, to

Table 6.1. Summary of Sony's "planetary-friendly" CCD chips.

Chip Des.

Color

Pixels

Pix. Size (microns)

Sen*

Webcam Examples

ICX098BQ

Yes

640 x

480

5.6 x 5.6

100%

Philips ToUcam Pro Logitech

QC Pro 3000/4000 ATiK-

IC/Celestron NexImage

ICX098BL

Mono

640 x

480

5.6 x 5.6

250%

ATiK-1HS II

ICX098AK

Yes

640 x

480

5.6 x 5.6

75%

Vesta Pro/Vesta 675

ICX424AQ

Yes

640 x

480

7.4 x 7.4

75%

ATiK-2C/Lumenera 075 Colour

ICX424AL

Mono

640 x

480

7.4 x 7.4

180%

ATiK-2HS/Lumenera 075 B&W

ICX254AL

Mono

500 x

480

9.6 x 7.5

310%

SAC-8.5

ICX409AL

Mono

740 x

570

6.5 x 6.3

370%

Astromeccanica KC381

* The "Sen" rating is calculated by the author taking into account the parameters from the Sony data sheets. It is an approximate indicator of the relative sensitivity of the CCD chips with a planet covering the same number of pixels. The popular ToUcam Pro is rated as 100% as the standard. Not surprisingly, the monochrome CCDs are the most sensitive as they are unfiltered. In practice, these CCDs will be filtered by the user to obtain an RGB or LRGB image. The monochrome ICX254AL and ICX409AL detectors are the most sensitive CCDs used in astro-webcams but have the disadvantage of having nonsquare pixels and so need resampling by the users software.

* The "Sen" rating is calculated by the author taking into account the parameters from the Sony data sheets. It is an approximate indicator of the relative sensitivity of the CCD chips with a planet covering the same number of pixels. The popular ToUcam Pro is rated as 100% as the standard. Not surprisingly, the monochrome CCDs are the most sensitive as they are unfiltered. In practice, these CCDs will be filtered by the user to obtain an RGB or LRGB image. The monochrome ICX254AL and ICX409AL detectors are the most sensitive CCDs used in astro-webcams but have the disadvantage of having nonsquare pixels and so need resampling by the users software.

reduce the long exposure thermal noise problems. A few of these products are of interest to the planetary imager, too, especially where a sensitive monochrome CCD chip has replaced the commercial color detector. Celestron's NexImage (Figure 6.1) has proved an attractive package because, although it is only a ToUcam Pro electronically, it comes as a bundle with a telescope compatible 31.7-mm nosepiece and with Registax software. It is not difficult to acquire adaptors or the Registax freeware but many consumers, especially novices, seem attracted by an all-in-one planetary imaging package, ready to go. But what are the alternatives to the off-the-shelf and cheap ToUcam Pro, Logitech QC Pro 3000/4000, and NexImage webcam devices?

Perhaps the most attractive unit here is ATiK Instruments' ATK-1HS II camera (Figure 6.2). Essentially it is a monochrome ToUcam Pro, with the Sony ICX098BQ CCD chip replaced with an ICX098BL and fan cooling added. The extra sensitivity gained with the monochrome system might seem pointless at first. After all, if you have to filter the monochrome detector to recover a color image then surely you are back to square one? Well, not quite. Remember the world's top imagers, like Damian Peach, use LRGB, not RGB. The colors in the image come from a filtered result, but the luminance can be unfiltered or in the passband that the planet has the most contrast/sharpness (e.g., red for Mars). Also, remember that unfiltered CCDs are very sensitive in the far red end of the spectrum and seeing is better there, too. As another consideration, bear in mind that the Bayer Matrix (Figure 6.3) and YUV decoding/compression system used in color webcams results in a very noisy

Figure 6.1. Celestron's NexImage imager is, essentially a sensitive webcam with a telescope adaptor and all the software provided. Image: Celestron.
First Atik Webcam
Figure 6.2. The author's monochrome ATiK 1HS super sensitive webcam. A low-cost way of taking planetary (USB) and Deep Sky (Parallel port) images. Image: Martin Mobberley.

Figure 6.3. A Bayer Matrix. The pixel filters on a typical color CCD chip are arranged as shown. Every two-by-two block contains one red filter, two green filters and one blue filter. The onboard webcam processing chip on commercial webcams increasingly compresses the color (and luminance) data from this matrix as the frame rate increases. In addition, the YUV video coding system degrades the blue signal.

Figure 6.3. A Bayer Matrix. The pixel filters on a typical color CCD chip are arranged as shown. Every two-by-two block contains one red filter, two green filters and one blue filter. The onboard webcam processing chip on commercial webcams increasingly compresses the color (and luminance) data from this matrix as the frame rate increases. In addition, the YUV video coding system degrades the blue signal.

blue image and lower color resolution than luminance resolution. Finally, monochrome webcams can easily be used (and are often supplied) in RAW mode (see Chapter 8) in which there are no compression/artificial sharpening algorithms and the image is far less noisy. When you have seen a noisy Saturn at f/40 in a ToUcam Pro webcam and then in an ATiK-1HS II you will see what I mean. The monochrome image is far smoother. A proper RGB image taken through color filters contains far more data, too, 24 bits (3 colors x 8) or even 30 bits (3 colors x 10) and with no data compression, especially with USB 2.0. Having said that, taking a tri-color image is far more hassle, especially in the case of Jupiter where the imaging window lasts two or three minutes (see Chapter 13). However, monochrome webcams have other advantages too. Scientifically important results can be obtained by imaging planets at the extreme ends of the spectrum. For example, Jupiter can be imaged in the Methane bands at 619, 727, or 890 nanometers; the 890 band is where methane gas absorbs light the most and is well into the infrared, providing a real challenge even for red-sensitive CCDs. Venus' cloud belts reveal details at the other end of the spectrum, i.e, in the ultraviolet. Only one filter at a time is required (not three as in RGB) for this type of work and a monochrome detector is therefore ideal. The color filters covering every 2 x 2 pixel block in the color Sony chips are red (one pixel), green (two pixels), and blue (one pixel). Thus, every pixel is filtered in some way. Adding another narrow band filter at the end of the spectrum will really hammer the response of a color webcam and a monochrome camera will perform far better for scientific narrow-band work.

One of the beauties of a webcam imager like the ToUcam is its light weight. Even the flimsiest telescopic set-up does not need strengthening or rebalancing when a ToUcam webcam is added. However, when a filter wheel is also added and filters are selected during imaging, a lightweight system may be compromised, especially when the field of view is only one arc-minute; even the slightest force applied to a telescope on a flimsy mount, especially a long Newtonian, can push the planet out of the field.

The ATiK system offers a lightweight and inexpensive filter holder that can be inserted between ATiK camera and telescope drawtube. Obviously any additional light path travel between Barlow/Powermate and CCD chip increases the effective f-ratio, so the thinner the filter holder/wheel the better. A slimline, lightweight, motorized filter wheel is, perhaps, the best system.

An extra bonus of the ATiK system is that, by connecting the parallel port supplied with the camera, single-shot exposures of several seconds can be employed too, for example, when imaging through narrow-band filters or recording faint planetary moons. (If you are buying a modern laptop, check it still has a parallel port if you have a parallel port camera; many modern laptops do not and a USB port replicator may be needed.)

ATiK offer four different "modified webcam" type cameras. In addition to the ATK-1HS II, which I think of as a monochrome fan-cooled ToUcam, they also do the 5.6 micron pixel ATK-1C II. This is essentially just an air-cooled color ToUcam Pro with a telescope adapter and a long exposure capability. The remaining two ATiK offerings feature 7.4 micron pixel versions of the above cameras, designated the ATK-2HS (mono) and ATK-2C (color). These type 424 chips cover almost 75% more area than the 098 detectors and have a physical imaging area of 4.7 mm x 3.6 mm, which could be a consideration for the deep sky imager. But the CCDs are no more sensitive in use than the 5.6 micron pixel ATiK devices.

Another couple of interesting Sony CCD-based USB cameras, this time made by a Florida-based company, are the SAC 8.5 and SAC II. The SAC 8.5 uses the ultra sensitive ICX254AL EX-VIEW HAD monochrome Sony chip, which is about 20% more sensitive than even the ICX098BL. However, the ICX254AL does have non square pixels, which may be off-putting for some. Resampling the pixels to produce the correct aspect ratio is a formality with modern software but many will still prefer square pixels so they have the same resolution sampling in horizontal and vertical axes. Like the ATiK 1-HS II camera range, the SAC 8.5 has a filter holder for RGB, LRGB, CYM, and LCYM imaging, although in the case of the SAC unit an actual filter wheel is involved, so there is less chance of losing the planet when you insert the new filter in place, and less chance of dropping the filter. As with ATiK's devices, the SAC 8.5 can be used for planetary imaging with rapid AVI download or for deep sky imaging, and the price of under $600 is a lot less than the price of the non-interline, Kodak chip-based cameras. The SAC 8.5 is fairly unusual as it features Peltier, not air cooling, in this economic price range. An even cheaper unit, specifically for planetary imaging, is the SAC II. At the time of writing, this new camera was just being introduced and featured 24-bit color imaging at the remarkable price of $149.

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