A teleconverter (sometimes called tele extender or TC) is a secondary lens which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image. They usually come in two lengths, 1.4 and 2X. These numbers represent the multiplier effect of the teleconverter. For instance, a 1.4 TC on a 100mm lens would make that lens operate like a 140mm lens. A 2X TC on the same lens would make that lens operate like a 200mm lens.
As I’ve grown older, I have come to rely on teleconverters. In the past, I’vd had a love/hate relationship with them. When I was a young man and dead broke, I used them to try to get more focal length and hated the results. Then again, when I was young, the quality of the average teleconverter was horrible and my technique not much better.
Now, decades later, teleconverters from manufacturers like Olympus are very, very good. (There are other good teleconverters from other manufacturers but I mention Olympus because I am most familiar with them.)
With the advent of higher-quality TCs and practice, I have come to the conclusion that with proper technique, and a super sharp lens to connect with the teleconverter, this gear can deliver sharp, pleasing image quality. The caveats are that you start with quality glass and use a properly matched teleconverter, i.e., one made by the same company that manufactures your lens. While technically, other brands may work, in my opinion, best practices require a properly matched converter.
Proper technique is also really important. For those who only use long lenses occasionally, its very hard to develop good technique. When I teach at bird photography workshops the first thing I tend to note with new students is their assumption that their expensive telephoto lens will be all they need to get a good, sharp image. If only that were true.
You really need to practice with long lenses and get your technique down. Use a sturdy tripod, and preferably a gimbal head if you're shooting with DSLRs. (Mirrorless shooters may be able to hand hold but a tripod and gimbal are always nice perks if you can afford them.) Place your feet shoulder-width apart, press your eye firmly to the back of your camera and drape your arm over the center of gravity on the lens. If youre making any sort of image other than a static, locked down image, and youre using a modern lens, go ahead and turn on IS. (Check your camera/lens manual to see if your stabilization works on a tripod.) These are minimum techniques for good image making with long telephoto lenses. I use a 1.4 TC on my Olympus camera. In the past I worked with a 2X teleconverter. Once you add that 2x TC to the equation, it only gets harder. When you use a 2X teleconverter you magnify EVERY mistake you make for all to see.
When you use a teleconverter you will end up short a stop or two of light. A 1.4 TC will cost you one stop of light and a 2X TC will cost you two stops of light. Most people already know that. What few people talk about is that you may also lose autofocus or at least autofocus speed. You may also lose some of your autofocus points. (My Olympus camera doesn't suffer from this problem but most do.) If you’re shooting with an older camera and lenses slower than f/2.8 pay attention to this.
I want to clear up a misconception. I have seen many photographers flatly state that teleconverters don’t offer autofocus on lenses slower than f/2.8. While this may be true for a majority of cameras its not true with some of the more modern high-end cameras.
Even if your camera can autofocus using a teleconverter, remember you will also be penalized by slightly slower autofocus acquisition. It is lens, body and situation dependent but it is something to know. I am lucky in that on my Olympus OM-D E-M1 Mark II, paired to the Olympus M.Zuiko Digital MC-14 1.4x Teleconverter this isn't a real issue. I don't notice any difference.
Back when I shot on DSLRs, a 400mm f/4 lens with a 1.4TC (EFL of 560mm at f/5.6 due to the one stop of light lost to the TC) will not yield autofocus that is as fast as a 600mm f/5.6 lens without the TC. The gaps grow closer every year and it’s much less of a problem with new gear. Older cameras/lenses/converters will be more likely to manifest slower AF acquisition.
It’s possible to use TCs with any variety of lens and camera combinations (check your owners’ manual to make sure your camera and lens pairing is compatible.) Some photographers are even able to stack two teleconverters (a 1.4 TC plus a 2X TC) to get even more reach. I have never tried this but you may want to. (Put the 2X on the camera, attach a 12mm extension tube to the 2X TC and then attach a 1.4 TC to the 12mm extension tube.)
When I attach a teleconverter I tend to attach the TC to the lens first and THEN to the camera. On some cameras, this seems to make a big difference in how well the TC talks to both the lens and the camera, in terms of autofocus speed and also in terms of metering. Consider this a best practice just to be safe.
With my desire to shoot long lenses I am constantly battling the need for big, heavy glass with the need for something that isn’t too expensive and that I can more easily carry. I have increasingly moved to using teleconverters and with practice, most photographers will find this is a reasonable compromise.
Scott Bourne Bio
Scott Bourne is an Olympus Visionary and a professional wildlife photographer, author and lecturer who specializes in birds. He was one of the founders of This Week In Photo, Founded Photofocus.com and is co-founder of the new Photo Podcast Network (www.photopodcasts.com.)
Scott is a regular contributor to several photography related blogs and podcasts and is the author of 11 photography books.
Scott is available to speak to your birding group, photography group and for both private and small group bird photography workshops. For more information on engaging Scott as a speaker or workshop leader, or for image licensing and print information, please e-mail firstname.lastname@example.org.