Long Lenses On The Cheap Page 2
3. Digital Lens Extender
If you have a 35mm SLR and like working with long focal lengths, you should consider getting a digital SLR body of the same brand. Most lower-cost digital SLRs have image sensors that are smaller than a full 35mm film frame. For example, my digital SLRs have image sensors that measure 22.5x15.0mm, while a 35mm film frame measures 36x24mm. These smaller image sensors "see" a smaller portion of the image formed by any lens, in effect increasing its focal length. Any lens I put on my digital SLR frames like a lens 1.6x longer on a 35mm camera: For example, my 300mm telephoto frames like a 480mm lens when I use it on the digital SLR. (Note that this 1.6x focal length "increase" isn't an actual increase in magnification. The raw image produced by the lens is the same whether it's used on a film camera or a digital camera; the digital sensor just crops more tightly into that image.)
True, a digital SLR camera body costs $800 and up. But so do really long lenses. And the digital SLR option not only effectively makes all your lenses longer; it gives you a darned good digital camera, too!
Another solution for the budget-minded long-lens fan is the mirror lens. Mirror lenses cost a lot less than refracting telephoto lenses of equal focal length, and generally focus much closer. (Yes, mirror lenses are shorter than their focal lengths, but no, they aren't "telephotos"--different optical design.)
On the down side, mirror lenses are not quite as sharp as good refracting lenses of equal focal length, and are somewhat slower. And mirror lenses have a fixed aperture; you adjust exposure via shutter speed alone, or by using neutral-density filters (some mirror lenses have such filters built-in).
Yet another good way to get long-lens shots without buying a long lens is to rent one. Some camera stores have rental departments, and if you need a really long lens (or just want to try one out), you might well be able to rent one for a day.
Telephoto, or just Long?
Photographers often refer to any long lens as a "telephoto." But not all "telephoto" lenses are telephotos. "Telephoto" refers to a particular optical design, in which the lens' physical length is shorter than its focal length--the "optical center" of the lens is actually in front of the front element. Most long lenses for 35mm cameras are indeed telephotos, but not all are.