image circle relative to focal length/fstop

How can I quickly determine the size of the image circle for a given focal length and f/stop. I want to be able to keep an image circle from getting too big, i.e. I want it to be 2' or 3''. Any quick help would be appreciated as would simple rules of thumb as opposed to some of the derivative calculus I sometimes see. Thanks for your help in advance. Thom
Received on Mon Mar 25 21:31:29 2002