Is magnification only because of the smaller viewing angle? Don't we have to take the resolving capacity of the optical elements and the design into consideration? Leaving DOF aside, when let's say you want to take a portrait shot, does the camera to the subject distance with a 35 mm. camera and 120 mm. lens equal D1 and 80 mm. lens? > -----Original Message----- > From: owner-photoforum@listserver.isc.rit.edu > [mailto:owner-photoforum@listserver.isc.rit.edu] On Behalf Of > Rob Miracle > Sent: Friday, September 06, 2002 5:18 PM > To: List for Photo/Imaging Educators - Professionals - Students > Subject: RE: Digital Cameras-Equiv. focal length revisited > > > 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 > > --- > Incoming mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.385 / Virus Database: 217 - Release Date: 04.09.2002 > >
