DSLR accessories

DSLR teleconverter

Written by Gail Bjork

A teleconverter increases the focal length of an interchangeable lens, but it also reduces the effective aperture size, magnifies aberration created by the main lens and may interfere with autofocus.

TeleconverterMany photography teachers talk about “zooming with your feet” by walking closer to and further from your subject instead of purchasing large and expensive zoom lenses. Sometimes, however, this is simply not possible and a longer focal length is needed to capture a particular scene. A teleconverter can help in these situations by increasing the effective focal length of a lens.

A teleconverter lens is mounted directly on the camera, and the lens is mounted on the teleconverter. They usually come with multiplication factors of 1,4x, 1,7x, or 2x and increase the focal length by this factor.

Teleconverter quirks

But teleconverters also reduce the effective aperture by the same ratio, so an f4 lens will become an effective f8 lens with a 2x teleconverter (two stops). Teleconverters also magnify any aberration created by the main lens. However, sometimes using a teleconverter is the only way to capture a specific scene adequately.

Teleconverters and lenses

Current teleconverters can communicate seamlessly with the lens and camera, particularly when they are made by the same manufacturer.  Older models sometimes prevent auto exposure and auto-focus, and not all teleconverters work well with all lenses and can even slow down auto focus speed.

Teleconverter lenses are most useful on fast lenses, or when taking photos in bright light. They generally work better on fixed focal length lenses than zoom lenses.

About the author

Gail Bjork

Gail Bjork, who is passionate about digital photography, is the owner and editor of Digicamhelp.Gail is the author of three illustrated ebooks about digital photography. A number of her photos and digital photography related articles appear at other websites.In 2006, a series of her photos, People in the Louvre, were exhibited at the Underground Photo Gallery
in Iisalmi Finland. Eight of her photos taken in the Florida scrub are on permanent exhibition at Parrish Medical Center in Titusville, Florida.Gail served twelve years as an elected member of The School Board of Palm Beach County, Florida, one of the largest school districts in the U.S. She has also been the editor of a small town newspaper and a free-lance writer. Gail and her husband owned and ran several small businesses.