Unfortunately, many of these “elite” manual-focus and specialty lenses aren’t available in mounts for modern DSLRs. Fortunately, there’s a simple and inexpensive solution: the lens adapter. Lens adapters let you attach lenses that weren’t made for your camera to your DSLR. They’re available from a number of manufacturers, and permit using a wide range of lenses—classic and the latest—on a wide range of DSLR bodies. Just attach the appropriate adapter to the lens, then attach the adapter/lens combo to your camera.
Besides letting you use older lenses on newer camera bodies, adapters also expand the range of current lenses available for new cameras. For example, the Micro Four Thirds System is fairly new, and relatively few Micro Four Thirds lenses are available. But simple adapters make it possible to supplement those with the full range of standard Four Thirds System lenses (retaining full automation, including autofocusing capability with most of them). Sony’s new NEX-series mirrorless cameras (which, despite their tiny size, contain DSLR-sized APS-C image sensors) expand the initial NEX lens offering via an optional adapter that permits using Sony’s much wider line of Alpha DSLR lenses with them (albeit without autofocusing). Because the mirrorless cameras have relatively short flange back distances, just about any SLR lens for which an adapter is available can be used with them. You’re unlikely to use a Micro Four Thirds camera as a primary body, but they make great compact backups and are useful as dedicated “still- and motion-capture” devices. With an adapter, you can dramatically increase their usefulness.
Flange Back Distance
The “flange back distance” is the distance between the lens mount and the image plane—the image sensor, in a DSLR. If the adapter is too thick, the flange back distance will be too long, and the lens won’t focus out to infinity. If the adapter is too thin, the flange back distance will be too short, and the lens will focus “beyond infinity.”
The first problem (inability to focus out to infinity) is the more serious, as it renders the lens/adapter/camera combination suitable only for close-up work. Careful manual focusing can solve the problem of combos that focus beyond infinity.