At 08:23 AM 9/6/2002 +0300, you wrote: >When I was talking about magnification, I was thinking about the >magnification effect of a telephoto lens only (like viewing a remote >object through a binocular). Is this what you were calling Optical >magnification? It seems I lack some theorethical knowledge here. If you think about what binoculars or telescopes do, they take a narrow angle of view and make it cover an area (your eyes). The smaller the angle of view the larger the perceived image is to the eye. They use a series of optical lenses to focus this narrow angle of view making it appear larger to your eye (the film plane). With digital cameras the "eye" is smaller my a measured amount. Using the D1 family which I'm familiar with, its 24mm wide as opposed to 36mm for 35mm film. Thats a 1.5X difference in eye size. When figuring out what the new angle of view is for the lens to the eye size, it in effect multiples the focal length by that factor of 1.5X. Other digital cameras have different factors. I use the D1 because 1.5X is a much easier number to work with than some other cameras. The reason I qualify the difference between optical and mathematical is that there are side effects to using lenses to enlarge things. Primarily the depth of field gets narrower and narrower the more optical magnification is used. In the case of using a smaller eye with a lens designed for a larger eye, those side effects like DOF don't change because of the smaller eye. This is where most of the confusion comes from and why I like to get people thinking about it from a math stand point and not an optical stand point. The lens doesn't change, its meaning does. Rob -- Rob Miracle Photographic Miracles 203 Carpenter Brook Dr. Apex, NC 27502 http://www.photo-miracles.com
