[ATMoB-discuss] DSLR able to be used for astrophotography

[valleli at rcn.com]

Bern,
On reaching 8 megapixels, the only thing needed is a large format such as a 35mm full frame format. 
More pixels mean excessive time spent downloading images which limits the number of frames that can be taken in the presence of skyglow. The result is noisy grainy pictures. 
The Canon 20D that Al Takeda and I have has been replaced by the 30D, which allows live images for focusing purposes. The Nikon D70 is what Phil R. has and that is now replaced by the D80.   

There are many hundreds of models below those costs, but they all have an important features missing. Many would be fine for bright objects light planetary and lunar photography. 
The accepted progression is:
 1. a webcam for high resolution video using Registax.
2. A low end DSLR or fixed lens CCD for eyepiece projection.   
3. A DSLR coupled with an apochromatic lens
4. An SBIG, Apogee, Adirondack Video CCD under laptop control.

It would take many pages to list all the possible features. 
Most color cameras have a Bayer filter matrix which greatly limits the scientific use - untenable for Photometric or VSO's.
Even the SBIG is unusable for this app unless refitted with Bessel-Johnson wide band filters. ( SBIG provides dielectric coated filters which have weird photometric curves - too spikey.

My Canon 20D has reflex mirror lockup but requires a $220 controller to activate several timing features such as bulb/long exposure settings.

In addition to the 400mm F/5.6 long lens ($1100) I had for the eclipse, I have just ordered a Canon 100mm F/2 for $400 for Comet photography. 
I have not been able to interface an old 50mm F/1.2 FD lens because of inadequate back working distance. The old 55mm F/0.9 is virtually unavailable at an affordable price. It was originally about $500 but now goes for over $3000 on the used market.

The new Canon EF series 50mm F/1.2 is $1600.

Zoom lenses have spectactular focal ranges like 18 to 85mm but all work at F/4.5 or slower. 

Large apertures are required for faint stars, fast F/no. for recording nebulosity like auroras.

Most compact, lightweight cameras have too few overides. My Nikon S4 with 10:1 optical zoom cannot adjust its shutter speed manually or take time exposures beyond a few seconds.

So generally, the less money you spend, the less satisfactory the camera will be. And, in one year, it will be obsolete.

Paul