Optimum FWHM vs Seeing

M Hambrick

What is the conventional wisdom on the lowest achievable FWHM at different degrees of seeing ? I am assuming that this is being done with a good scope (e.g. 92 mm Stowaway), and relatively short (< 10 second) focusing images. The best I have been able to get is a FWHM in the range of 1.20 to 1.30, but more often it is in the range of 1.50 to 1.80.

As a follow-up, is there an upper limit for FWHM above which there is no point in trying to do any imaging ?