I previously was under the impresson the the diaphragm opened when the picture is taken. I theorised that a fast lens was fast because a diapragm opening to f/1.4 @ 1/1000 would be faster than a lens that opened to f/5.6 @ 1/1000. Obviously that isn't the case. There is much that I do not understand regarding the physics of light. It just seems from a non-engineering point of view that building a lens with a large aperture shouldn't be any more expensive than a lens with a small aperture. Kevin -----Original Message----- From: Ernest Nitka [mailto:enitka@twcny.rr.com] Sent: Tue 12/24/2002 12:17 PM To: List for Photo/Imaging Educators - Professionals - Students Cc: Subject: Re: Fast Lenses: Why so expensive? Kevin - simply put the faster the lens the more correction has to be designed into the lens so the distortions don't get the best of the image. The opposite of this design requirement is the pin hole camera - a hole without a lens at say f/256 will give you an image albeit not terribly sharp. The more technical on the list can give you all the technical reasons. ernie
