[Shiraz (Ray)]

Hi

Have been working on a simple spreadsheet for calculating the optimum pixel size for imaging, based on maximising both resolution and signal-to-noise ratio and accounting for optics resolution, atmospheric seeing and tracking wander. The attached table shows the results for a few combinations of scope+mount and in 2 and 4 arc sec seeing (FWHM). A few simplifying assumptions went into this (eg perfect scope assumed, secondary obstruction ignored, sensor cross-talk not considered). However, the results should not be too far from reality.

Interesting how dominant the atmosphere is, how much effect the mount has in good seeing and how similar the final resolution is for the chosen scopes -even the AAT resolution is not dramatically better than a C11 in 2 arc sec seeing.

The standard rule of thumb of 2 arc sec per pixel might be a bit coarse - probably better to use something around 1 - 1.5 if you expect reasonably good seeing.

Most of the Sony sensors, the Kodak 8300 and older DSLRs would appear to be well matched to the shorter focal length scopes at around 5 microns pixel size. If you have a longer fl scope (SCT or RC), you will be best off with one of the bigger pixel Kodak sensors, or use binning. The optimum for a very fast scope (eg hyperstar) would be one of the new generation chips with small pixels.

regards Ray