All about teleconverters: Wildlife photographer Steve Perry on maximizing a TC’s effectiveness

posted Sunday, June 30, 2019 at 7:30 AM EDT

When searching for a bit more reach with your telephoto lens, many sports and wildlife photographers opt to use a teleconverter. What is a teleconverter, what does it do and how does it work? In his latest video, wildlife and nature photographer Steve Perry answers these questions and much more.

A teleconverter is essentially a second lens you place in between your lens and the camera body to increase the focal length of your lens by the multiplication factor of the teleconverter. For example, a 1.4x teleconverter will increase the focal length of your 300mm f/4 lens to 420mm on a full-frame camera. Sounds great, right? Unfortunately there are drawbacks. The teleconverter also decreases the maximum aperture of your lens by varying degrees, depending on the magnification factor of the teleconverter. The popular 1.4x teleconverter reduces your maximum aperture by a full stop. Returning to the prior example, your 300mm f/4 lens with a 1.4x teleconverter is effectively a 420mm f/5.6 lens. You have more reach to get closer to your subject, but you also have less light gathering. Additional teleconverters include 1.7x and 2x teleconverters, which reduce the maximum aperture of attached lenses by 1.5 and 2 stops respectively. This means that a 400mm f/2.8 lens with a 2x teleconverter becomes an 800mm f/5.6 lens on a full-frame camera.

There are other considerations too. How does a teleconverter impact depth of field? If you compare a 400mm f/2.8 lens with a 2x teleconverter against an 800mm f/5.6 super telephoto lens, the depth of field for each lens will be the same. However, the image quality and autofocus performance is unlikely to be identical between the two lenses. When you add a teleconverter, there is also a drop in image quality. The impact on image quality of a teleconverter will depend upon the lens you are using and the teleconverter. Perry offers an informative breakdown of how a teleconverter works and why a TC will degrade image quality in the video below. To see how autofocus and other performance is affected by the use of a teleconverter, be sure to watch the full video.