pixel size of ccd vs resolution of scope vs general seeing

Certainly true. However, the cost of the CCDs seems to be more closely correlated to the overall sensor size, rather than the number of pixels on it. So a 7um-pixel sensor with 2k x 2k pixels binned 2x2 would produce the same result as a 14um-pixel sensor with 1k x 1k pixels, only the binned one would have more sensitivity (and slightly more cost). Do I have that right?

Well, there aren't too many cameras with large pixels (the SBIG ST9 and a couple of the FLI ones are exceptions). The astrophotography trend in general is primarily aimed towards imaging with small to medium sized apos. The number of small-sized apos on the market now is phenomenal and growing dramatically in terms of number and quality. These have focal lengths in the order of mm, rather than metres, so require a chip with small pixels in order to get the resolution right. It also makes the job alot easier from a tracking/guiding point of view and alot less taxing on the mount. The key here though is that you select an imaging system with the correct resolution - if you use a chip with large pixels on a small apo, will you fail to get alot of detail. Same would happen with a chip with small pixels which was then binned. Yes, the sensitivity goes up, but at the price of resolution.

If you only want to view your images on a screen, then something in the 1k x 1k pixels or so would be fine. Monitors are of course getting bigger too, so one needs to bear that in mind.

Imaging at a slightly higher resolution and then scaling down slightly after has the advantage that you can process the image to the last at the full scale, and then size down slightly to hide any small little flaws in your processing skills as the noise/errors can get smoothened out too.

Of course, it can go too far too. Cameras have now come out with sensors of 4 mega pixel, 6 mega pixel, etc and with small pixels to boot. If you want to look at the image in it's entirety on a screen, then you will run into difficulty. You will then start down-sizing the image in Photoshop so that you can see it all - this however will lose the resolution in the image.

So, to put a long story short, cameras with large chips aren't necessarily the perfect solution for everyone.

Michael --

Yeah, the big pixel thing is kind of my issue -- it's a pity there aren't more options available. While I'll surely start imaging with the 800mm focal-length refractor, the goal would be to image at some point with the 4200mm MCT -- which would require a lot of binning or some mighty big pixels.

The other option, of course, is to get an imaging-specific scope with a focal length somewhere in between -- perhaps something along the lines of a mid-sized Mak-Newt. But then I'd need to build a second observatory as the big MCT is too heavy to mount/demount by myself.

Anyhoo, thanks for the info. Yet more to chew on....

-- Jeff