This might get you started ... http://www.vanwalree.com/optics/lenshood.html
However, it's so simple to put a hood on a lens and snap a pic. Be sure to focus to infinity and stop that puppy down to get a worst case scenario. Might be good to check the hood with a filter attached if you ever plan to use a filter. Shel " ............... " > [Original Message] > From: <[EMAIL PROTECTED]> > Is there anyway to tell how long a hood should be? Without vignetting? I have > a hood (non-rubber) for a longer lens that might work on a slightly shorter > lens. Is there some kind of mathematical formula? Or is the only way to tell to > take some shots?