RASC Montreal Centre - Articles

A couple of years back, astrophotography was revolutionized be the ingenuity of amateurs who took apart their webcams and started imaging planets. The results were incredible to say the least. The best webcam planetary images rivaled images taken with professional instruments using film a few years before. Now just about anybody can hook up their webcam to a telescope and get decent results; at the very least, results a lot better than anything they did with film.

This was not the case for deep sky objects (DSOs). DSO imaging is still the domain of the $5,000+ USD dedicated astro-cameras produced by SBIG, Starlight Express and the likes. Although, low end cameras have been available, new technology and amateurs willing to tinker have produced a new crop of imagers that will give the big boys a run for the money.

I bought a SAC 7b digital astro camera a few years back because I couldn't get out of town enough to enjoy observing and photographing the sky. My backyard is heavily light polluted, with a limiting magnitude of 3 to 3.5, if not worse; I live within 5 blocks of 3 major shopping malls and across the street from a soccer field! Visually, I can't see much even through my 10" scope, so I figured that doing digital imaging would at least let me enjoy some of the Messiers from home.

SAC imaging started producing webcam long exposure cameras for about $500 USD a few years back. Essentially, these are everyday webcams (same type as for planetary imaging) that have been modified to permit long exposures. These cameras were an excellent starting point for amateurs without ample disposable income. However, they did have their shortcomings and were still far from the capabilities of the SBIG-like dedicated cameras.

One of those shortcomings is that the SAC (and similar) cameras are currently 8-bit per channel. Think of the 8 bit as the number of shades available in a given colour. So 8 bit would give you 8 zones of red, 8 zones of green and 8 zones of blue, 16 bit would give you 16 zones of each colour. However, it's a little more complicated than that, but all you have to remember is that 8-bit cameras will give you 256 shades of grey in each of the colour bands; 16 bit will give you 65536 shades. Now, if you're doing planetary, this is not really a big issue, but for DSOs it means the difference between seeing "something" and seeing nothing.

My first image was less than satisfactory. I was expecting it to be relatively easy, like imaging Jupiter with my Toucam. I got a wake up call the first night out! Tracking errors in my mount became blatant on images, polar alignment became something that needed a little more care and then processing was a little more complex than just "taking" a picture. Then there are the perils that plague ALL cameras. First, you cannot see the deepsky object you are imaging on screen; second, you have to get pretty good focus, otherwise the stars in the image look blurry and washed out; and, thirdly, you have to have a mount that can track decently for the duration of the exposure, say 20 to 30 or more seconds. With planetary webcam imaging, the mount has little effect on 1/10 second or faster exposures.

Deepsky imaging will tax all the weak points in your system, but that does not mean that you can not work them to your advantage. The SAC cameras have two things going for them beside price; they have decent software which has many features (I'm still trying to figure them all out) and the camera permits you to make corrective adjustments quickly and on the fly.

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