[rogerg (Roger)]

I probably should know the answer to this, but feel it's worth a discussion to broaden my knowledge.

The golden rule once was supposedly "image at 2 arc sec per pixel".

However, if everyone was imaging at no higher resolution than 2 arc seconds per pixel there wouldn't be a resolution advantage in having a larger telescope yet it appears in practice there is a resolution advantage. Some people produce higher resolution images of small objects than others who are at about the 2" scale.

While I never subscdribed to the 2" rule I can see where it comes from - limitations of viewing conditions primarily, as I understand it. I find 0.8" is my limit.

Are large professional telescopes limited to similar resoultions? Or if not then is it only because they are at the top of a mountain or is it a factor of mirror diameter?

In practice is a 24" RC limited to the same resolution as a 12" RC?

So, how does someone increase their resolution per pixel while retaining a sharp image?

Does it come down to just adaptive optics and moving to a mountain top or is there a factor such as mirror size which does in practice have a material impact?

Resolution is a factor of focal length and pixel size, to my knowledge. While possible to choose a combination of long focal length and small pixel size (perhaps to reach 0.5" for example) this would result in a horribly poor quality image. But in practice is there a way for 0.5" to become usable?

Obviously quality of optics, tracking and equipment stability has a big impact but I'm choosing to ignore these for this example and they are not variables I am intending to discuss.

I should also clarify I'm considering deep space CCD imaging. Not visual and not planetary. Although, it's interesting how planetary imaging compares, where the resolution is pushed to the physical limits of the telescope and perhaps only compensated for by increased number of frames hence increased SNR.

Regards,
Roger.