On Mon, May 25, 2009 at 11:01 PM, Bran Everseeking <[email protected]> wrote: > On Mon, 25 May 2009 16:04:16 -0700 > Joseph McAllister <[email protected]> wrote: > >> Telephoto lenses don't reach out, they narrow the usable field of >> view at the same time increasing resolution to render that field >> sharp. > > telephoto lenses do have a narrower FOV but the image on an aps > sensor/film with any lens is a crop of the image made with the same lens > on a 35mm sensor/film. thus the barrel in the centre of the image is > the same size... not larger as the implied 100=150 would have one > believe telephoto lenses provide magnification of distant views, reach. > > semantics are important if we are to understand one another. > > what you are saying does not match my understanding though may be only > different in dialect. >
Actually, telephoto lenses don't provide any inherent result that can't be achieved also by reducing sensor size or subject distance. Longer lenses provide narrower Fields of View. Reducing sensor size achieves the same thing. That's because Field of View is conditional on both focal length and sensor format. Change either and the same effect is achieved. Magnification is a matter of focal length and focus distance but that's irrelevant to the equation in when it comes to anything except working distance for Macro and Depth of Field calculations (Since DoF actually depends on aperture and magnification, not focal length). Technically, a telephoto lens is merely a lens which has an optical centre further from the focal plane than the physical centre of the optical group. It's possible to have a telephoto wide-angle lens, although that's a much more rare occurance than the opposite (a retrofocus lens which is also a long lens, like the Olympus ZD 25 Pancake and ZD 35/3.5 Macro or the Pentax DA 35 Limited). -- M. Adam Maas http://www.mawz.ca Explorations of the City Around Us. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
