At 01:20 PM 12/24/2002 -0500, you wrote:
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 toKevin, there are a lot of factors that go into lens costs. Lets look at a few things in layman's terms. A lens with a max opening of F5.6 has more depth of field than a lens of F2.8. The reason to buy a fast lens is to shoot it wide open typically. Focusing errors, lens aberrations and distortions show up in lens when they are either shot wide open or stopped down to their maximum. Thats why F8-F11 are considered the sweet spots in lenses. Most lenses are turned to produce the best picture at those F stops.
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.
The F2.8 lenses and faster have to be tuned for a wider range of apertures. Lens elements must meet much more stringent quality controls. The lens elements are bigger and harder to make. There are typically more elements to correct for various distortions along the way. The heaver glass needs more heavy duty gears and motors to auto-focus them. It all adds up to a more expensive lens.
Hope that helps explain it....
Happy Holidays,
Rob
--
Rob Miracle
Photographic Miracles
203 Carpenter Brook Dr.
Cary, NC 27519
http://www.photo-miracles.com
