A Quick Guide to Teleconverters

Published July 22, 2015

Teleconverter use and compatibility can easily get confusing. I’d like to shed some light on the subject for those looking to get more length out of their lenses without the extra weight or cost.

Teleconverters can add versatility to your camera bag by giving you extra length and a variety of looks out of lenses you already own. It can also mean a much lighter load  to carry through a wildlife excursion or golf tournament.


Nikon 2x Teleconverter Mounted Between Lens and Camera

What is a teleconverter?

A teleconverter, sometimes referred to as an extender, is a magnifying lens that mounts between a camera and a standard lens to increase the effective focal length.

How does it work?

The teleconverter multiplies the focal length of the lens. For example if you have a 300mm lens and you use a 2x teleconverter you have an effective focal length of 600mm (2 x 300= 600).

It will also reduce the f stop of the lens by the same number, meaning a 2x teleconverter will reduce the aperture by 2 stops. A 300mm f/2.8 lens with the 2x TC becomes a 600mm f/5.6 (f/2.8- 2 f stops = f/5.6). If you were using a 1.4x teleconverter you would only lose 1 stop of light (f/2.8- 1 fstop= f/4).

Here is a visual representation of the effect a teleconverter has on focal length.

Nikon 300mm                                               Nikon 300mm + 1.4x TC III (420mm)

Nikon 300mm+ 1.7x TC II (510mm)                 Nikon 300mm+ 2x TC III (600mm)

Nikon 600mm                                         Nikon 600mm + 2x TCIII (1200mm)

Below (left) you can see a 100% crop of the Nikon 300mm + 2x TCIII = 600mm and (right) Nikon 600mm. It’s apparent that there is not a big difference in quality; If you really strain your eye you can see a few more details without the use of the teleconverter. Results will vary of course as these images were taken with some of the best equipment available. In general when using any type of adapter between your camera and lens you can expect a level of image degradation.

Nikon 300mm + 2x TCIII                                                                    Nikon 600mm


Lets talk about compatibility. Not all cameras and lenses can use teleconverters. The first things to look at on lenses are the maximum aperture and the rear element. The maximum aperture is the f stop printed on your lens barrel indicating the widest your aperture blades will open. If it says f/2.8 you are in the clear. If the number is higher keep reading for compatibility options.

The rear element will also indicate if you can add a teleconverter. Your lens must have a recessed rear element as pictured on the right. If the glass is flush with the mount there is nowhere for the teleconverter glass to go and so you are physically out of luck.

Nikon 24-70mm f/2.8 (not compatible)                                    Nikon 70-200mm f/4 (compatible)

Most cameras lose the ability to autofocus at a maximum aperture  of f/8 , so the f number of your lens plus the light subtracted by the teleconverter normally needs to equal f/5.6 or less to maintain autofocus. For Example,  a 70-200mm f/4 with a 1.4x teleconverter has a max aperture of f/5.6 and can maintain autofocus. If it were paired with a 2x TC the max aperture would be f/8 and there would be no autofocus functionality with most current DSLRs. There are a few exceptions to this rule at the cost of losing most of your autofocus points.

Here is a list of some DSLRs that can focus to f/8 (limited to center point AF):

Canon EOS 1D Mk IV, Canon EOS 1D X, Canon EOS 5D III, Canon EOS 5DS, Canon EOS 5DSR, Canon EOS 7D Mk II

Nikon D4S, Nikon D4, Nikon D810, Nikon D800 (E), Nikon D610, Nikon D600, Nikon D7100, Nikon D7200

And to save you a little bit of trouble, here is a list of some popular lenses that are teleconverter compatible:

*Please note: Nikon teleconverters can only be used with Nikon Lenses

Sigma compatibility is available here.


Teleconverters are great for adding more versatility to your camera bag, without adding much weight. While you may lose a bit of  image quality, the benefits can more than make up for it. For more information on teleconverters, you can check out a previous post Teleconverters 101, and of course feel free to look at what we have in stock for Canon, Nikon, and Sony.


Author: Sarah McAlexander

I’m Sarah. I have a BFA in Photography from the University of Memphis. I’ve been shooting professionally for over 6 years. When I’m not working here or freelancing, I enjoy yoga and traveling.

Posted in Equipment
  • Frank

    Nicely enough, the Canon TS-E 17mm is also compatible with teleconverters. As with tele lenses, you loose a bit of quality, but it’s still fine afterwards.

  • Dan Wells

    Some of the initial spec sheets indicate that the new Nikkor 200-500 f5.6 may be teleconverter compatible. If so, that’s REALLY interesting – unlike any other lens short of $8000 exotics, it will autofocus at a maximum focal length up in the 700 mm range. All other zooms longer than 400mm (except for the VERY expensive 200-400 f4s, and a couple of Sigmas that are even more exotic (the 200-500 f2.8 and the 300-800 f5.6)) are f6.3 at the long end, so they are f9 with a 1.4x converter – no AF on any camera.By sticking to f5.6, the Nikkor seems to become a 700 f8. It would actually either be a little over 700mm or a little faster than f8, assuming the lens is honestly marked and depending on the converter design, because the increment in length to lose 1 stop of light isn’t 1.4, it’s the square root of 2 (1.414…). There isn’t even any prime lens that gets there without being a lot more expensive. A 400 f4 with a 1.7x would be around the same length and a little faster, but doesn’t exist that I know of other than the very large and heavy 200-400 f4 zooms (it would also be 800mm at f8 with a 2.0x). A 500 f5.6 would, of course, be the same as the long end of the Nikkor zoom, but also doesn’t exist. A 400 f2.8 or a 500 f4 are both MUCH more expensive, although common enough. A 400 f5.6 is only 560 mm with a 1.4x converter and won’t focus with anything more. There were a couple of manual focus 600mm f5.6 lenses (including at least one zoom), but none were ever made in autofocus versions, and a 600mm f4 is near the epitome of large, heavy and expensive!

  • Brian Caldwell

    Very nice article on TCs! One nitpick, though: when you state “In general when using any type of adapter between your camera and lens you can expect a level of image degradation”, its important to note that this only applies to teleconverters and not to high quality focal reducers.

  • Peter Dove


    A secret about TCs that surprisingly few people I run into know about is that they work just fine with tilt-shift lenses, if you’re into that sort of thing. They don’t just physically fit with the recessed rear element, they really work OK: optics, movements, metering and all. That’s with a 24mm T/S-E and 1.4x EF converter on a decrepit old 5D. (I’m not even curious about it at 17mm, though. Well, OK, I’m curious, but skeptical. Well… lemme check the rental page.) I presume Nikon et al. and other focal lengths will behave too. YMMV. There’s a little degradation in pixel-peepability at 1.4x and of course more at 2x, but it’s still not terrible in a non-huge print with the 2x TC. What shows looks like mainly enlarged prime lens aberrations more than additions from the TC. A newer higher-resolution sensor might allow a better print. The 1.4x is still plenty good enough to use. As Frank mentioned, the 24mm with the 1.4x TC usually works better than cropping, especially if you don’t have pixels (or a couple of kilobux) to spare and don’t need the wide-open prime f-stop right then and there. I don’t really bother using the 2x, though, just use the 1.4x and crop if needed.

    * Not safe for pixel-peepers.

  • I hope you paid joey a modelling fee

  • Tony

    I’m with Frank. When I’m out in the field, the decision I have needed to make is whether to mount a TC to my telephoto lens, or to simply do some deep cropping later. Then the discussion about the quality loss becomes about the lesser of TWO evils. With a very high quality prime lens, and if the target is very small (I’m looking at you, bird photographers) the TC just might win.

    One choice I’ve never had to make out in the field is between using a 300 + 2X vs. that 600mm that I forgot was sitting unnoticed in my back pocket.

  • Jack T

    Nice primer for those of us that have not ventured into using a teleconverter yet…thanks.

  • Derek

    Whoa, what a change of approach from the recent intense, mathematical/statistical articles that usually leave me shaking my head but appreciating somebody capable of undertaking them. I think a few numbers indicating reduction in quality would be useful here. I’m no math geek but it’s been a long time since I’ve accepted the quality drop off when using a teleconverter so I need to be convinced that the quality doesn’t drop enough to outweigh the advantages of added versatility. Your pictures seem to indicate a fairly significant drop in quality but I’d prefer to see a few numbers rather than trust my eyeballing.

    I’m curious how some of the newer superzoom, small sensor cameras compare against a good lens/converter combination at lower ISOs.

  • Sarah McAlexander

    Harry, This is not meant to be a complete list of compatible lenses, but I appreciate you adding to it!

  • Harry

    please at for Canon kompatible Lenses:

    2.0/135 mm L
    4.0/70-200 mm L IS
    4.0/70-200 mm L
    4.5-5.6/100-400 mm L IS II
    4.0/300 mm L IS
    4.0/400 mm DO IS II
    5.6/800 mm L IS
    4.0/200-400 mm L IS

    so it looks like Nikon has more compatible lenses, and that’s not true.

  • Jim Thomson

    Sean T Olympus has teleconverters for m4/3.

  • Sean T

    I can’t think of any TCs for use with mirrorless interchangable lens cameras. Am I missing something, or are these only for Canon, Nikon (and maybe Pentax and Sony)?

  • Next time you shoot with superteles, please use someone who understands how to hold the damn thing to minimize mirror flop echoes. These examples should’ve been pin sharp.

  • Claus

    As far as I know the Nikon D750 is also able to focus to f/8. Maybe you should add this camera to your list…

  • Frank Kolwicz

    An additional benefit of teleconverter use is in comparison to cropping to get the same level of magnification in a final image: in general, I believe it is better to suffer some optical degradation rather than lose pixels on the subject. Comparable cropping results in a drastic reduction of resolution compared to optical loss due to TCs.

    No, I don’t have technical data to back that up, but there’s a lot of discussion of it on the net and the consensus of posts with some rough calculations that I’ve read is as stated above.

  • Sarah McAlexander

    Thank you for pointing that out! I removed the words “round down” from the paragraph to avoid further confusion. It is simply the quick way I learned to remember the light loss for each teleconverter.

  • Jouko

    The f-stop effect explanation is somewhat inaccurate. You don’t “round down” the 1.4x effect to get a 1-stop effect, instead you use the same multiplier (1.4x) to both the effective focal length and the f-stop number (2.8 x 1.4 = 3.92, so approximately 4). If you look up what the f-stop number actually means and where it’s derived from, it’s quite obvious. Each f-stop multiplies the number with about x1.4 (sqrt(2) to be exact), and because 1.4×1.4~=2, the x2 multiplier has about 2-stop effect.

  • Caly Taylor

    Sarah – a good primer on teleconverters, especially the AF-compatibility part. A lot of photographers buy one without understanding that point.

    My only critique comes where you are discussing the light loss from adding a teleconverter, ” If you were using a 1.4x teleconverter you would round down and only lose 1 stop of light”. Round down? Ouch!

    The correct (and slightly techie) answer is that the light loss comes as the square of the teleconverter’s magnification:
    1.4 squared = 2, so the original lens is 2x brighter than the converted lens, and 2x dimmer for the new lens is equal to 1 f/stop light loss. Thus the 2x teleconverter is 2 squared = 4 times less light, which = 2 f/stops, and the 1.7 TC squared = 2.9, so you really can now round the number to a 1.5 f/stop light loss.

    Ok, I got that off my chest. Keep up the good work.

  • José

    Sorry Sarah, I didn’ty pay attention you wrote the article…

  • José

    Hi Roger!
    the Canon 180mm f3.5 macro is also compatible with the canon teleconverters (extenders).



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