I have a love/hate relationship with teleconverters (also called telephoto extenders or telex tenders – TC.) 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 Nikon and Canon are very, very good. (There are other good teleconverters from other manufacturers but I mention Nikon and Canon 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, 2X teleconverters can deliver sharp, pleasing image quality. That proper technique thing is 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 an assumption that their $5k, $10k, $15k 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. 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. These are minimum techniques for good image making with long telephoto lenses. Add a 2X teleconverter to the equation and it only gets harder. When you use a 2X teleconverter you magnify EVERY mistake you make for all to see.
Ive tested many teleconverters and generally believe that you are always better off (if you can afford it) using the most recent version of the brand of teleconverter that matches your camera. For the rest of this post Ill discuss the latest 2x TC from Canon – the Canon EF 2.0X III Telephoto Extender.
At $429 its not cheap, but then again, for my tests, the Canon EF 400mm f/4 DO IS II USM Lens isn’t cheap either at nearly $7000. Given the need to make super telephoto lenses more super, the cost of a high-quality piece of gear is justified when that gear is made of optical quality glass, has nine elements in five groups, is weather resistant and will autofocus on Canons pro bodies (like the 1DX) with any lens that is f/4 or faster (costing the f/4 lens two stops.) I have never been satisfied with the results from the cheap Chinese knock off converters and strongly suggest that photographers avoid these if possible.
When you use a teleconverter you will end up short a stop or two of light. What few people talk about is that you may also lose autofocus or at least autofocus speed. If youre 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 such as those from Canon in their pro-line. My 1DX can autofocus using only the center AF point (plus the four assist points if you set Canon’s AF Expand mode) at f/8 which means using the Canon f/4 DO II and dropping two stops of light I can indeed use AF with the 2x TC. Rumors have been circulating that the upcoming 1DX MK II will be able to use all AF points at f/8. If true, this would be a boon to users of long lenses and teleconverters.
When I attach a teleconverter I tend to attach the TC to the lens first and THEN to the camera. Especially on Canon gear 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.
In the scenario I describe here, shooting a 400 F/4 lens with a 2X TC I have an equivalent focal length (EFL) of 800mm at f/8. Great technique is a must when shooting with this combo.
To give you an idea of how important this is, look at the picture below. It is a simple photo of a sign made with the Canon 1DX, the 400 f/4 DO IS II lens and the newest Canon 2X teleconverter all mounted to a sturdy carbon fibre tripod with a gimbal head attached. I locked down the shot and used the self-timer to make an image. Note that even with everything locked down and with no pressure from my finger rolling over the shutter button, there is some blur in the subject due to camera movement.
Now look at the next image. While its counterintuitive, I made the next shot with the camera a little loose on the tripod but I pressed my eye to the back of the camera and let my arm rest over the center of gravity on the lens. This actually yielded a sharper result.
Lets look at another image. This picture of some fake flowers in a box was spotted near the waterfront where I live. Note that the background has completely disappeared even though this shot was made at f/8. If you have enough distance between your subject and the background, even a smaller aperture will allow for a pleasing, blurry background.
Lastly lets look at sharpness. This is a 200% (no extra sharpening except for the auto-import baseline sharpening in Lightroom) crop from the same image displayed here to show that even with a 2X teleconverter, there is plenty of detail to be had.
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.
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