Not sure what you mean by this - image scale is image scale.
Run some examples through to verify this.
In the example provided by the OP - The image scale is the same !
You will get EXACTLY the same image from both of them - if both cameras have the same number of pixels.
Both image scales are EXACTLY 0.69 arcsecs/pix, 7.3 x 7.3 arc mins fov on a 640x640 array.
The f6 system is concentrating its light onto larger CCD, the f3 onto a smaller one !
I didn't assume the performance of the two CCDs was the same - I said they were very different and why.
9uM pixels may be ideal for some situations, but definitely not all of them.
Sometimes 24uM pixels are best and other times 2uM pixels are best.
Its a question of selecting the ideal sampling rates and image scale for the OTA and the intended purpose. Not to mention CCD specs such as spectral response, Qe, budget etc
So yes a different choice of CCDs on the same OTA is necessary for Planetary or DSO or Widefield Vs Narrowfield etc, but that is not what was being asked.
I think the OP's choice of pixel sizes used was purely hypothetical to illustrate problem, but Lumenera have a number of 4um cameras for Astro use as do others and there are probably dozens of point and shoots in the 2um size range.
Originally Posted by gregbradley
I think its not that cut and dry.
Depends on the target. Some targets are widefield with bright and dim areas.
If you zoom in (F6) you may be imaging part of the dim area. If you zoom out (F3) you would be taking in more of the bright areas and therefore more signal and it would expose faster (not the dim areas though).
Of course you are assuming even performance of 2 sensors one with half the size pixels of the other and we know that is rarely the case.
9 micron pixels seems to be the allround winner in cameras. Theoretically smaller pixels should work better in a faster system but Kodak chips seem to perform best around the 9 micron pixel size. Perhaps a characteristic of their architectural design?
Kodak went to 5.5 micron pixels with their true sense sensors. These sensors only now seem to be coming out in cameras despite being around for quite some time. It takes the market a long time to accept new products like that.
Of course there are no popular cameras with either 4 or 2 micron pixels out there. The smallest Kodak is 5.4microns. Not sure about Sony - they may have some in the 4+ micron band.