Teleconverters: Which Lenses They Fit and What You Lose

Updated October 27, 2026 · CameraGear editorial · Contains affiliate links

A teleconverter is a small optical unit that sits between the camera and the lens and multiplies the lens's focal length. It is usually cheaper than buying a longer telephoto, but it costs light, it can limit autofocus, and it fits only a limited set of lenses. For most people the question is not "is it good?" but "does the maker list it for my exact lens, and can my camera still focus with the darker image?"

If you are still choosing a telephoto, start with our budget telephoto guide. This article is for readers who already own or are about to buy a lens and wonder whether a converter is the cheaper way to get more reach.

What a teleconverter does

Per Wikipedia's teleconverter article, a teleconverter is a secondary lens mounted between the camera body and the main lens, enlarging the central part of the image. Common strengths are 1.4x and 2x. A 2x unit doubles the lens's apparent focal length. The article calls them usually cheaper than a longer telephoto, and notes that teleside converters, which mount on the front of the lens, are a different type.

This guide covers the rear type that sits behind the lens. Front-mounted converters are a separate product and have their own limits.

What you lose: light

The article states that light intensity falls with the square of the magnification. For a 2x converter, that means a quarter of the light and a doubled f-number. Here is the arithmetic, using round examples to show the pattern, not a claim about any lens:

The 1.4x row follows from the same square rule (1.4 squared is close to 2). Read it as arithmetic, and check the lens maker's information for exact figures. The practical effect is slower shutter speeds or higher ISO for the same exposure, which matters in poor light and with moving subjects.

What you may lose: autofocus

The same Wikipedia article says that with slower lenses, the reduced effective aperture can stop autofocus from working, and puts the threshold somewhere between f/5.6 and f/8 depending on the camera system. That is a general range from a secondary source. Your camera's manual states what it supports.

The sequence to check is simple: take the lens's widest aperture, apply the converter's effect from the table, and compare the result with the narrowest aperture your camera is documented to autofocus at. A lens that opens wide leaves room for a converter. A lens that already opens narrow may leave none. Our guide to how autofocus works explains why less light slows or stops focusing.

Image quality

Wikipedia says a converter also magnifies the lens's aberrations. It states that it halves the main lens's resolution, though the digital image's resolution may not be halved, and that the image becomes darker. The better the main lens, the better the result usually looks, so a converter is a trade, not a free extension. Sharpness also depends on how still you keep the setup; see tripod load ratings for a heavy lens-and-converter stack.

Which lenses a converter fits

The article says dedicated teleconverters work with only a limited number of lenses, usually telephotos from the same manufacturer or from third parties built to a matching standard. That is the key point for compatibility, and it has three practical consequences:

• Go by the maker's list. A converter should name the lenses and cameras it works with. A mount match alone is not enough.
• Check the exact lens name and version. A converter listed for one version of a lens may not be listed for another.
• Check the converter's strength. A lens may be listed for 1.4x but not for 2x.

Because the converter sits between the camera and the lens, the lens has to be designed to work with it. Neither source gives a rule for which lenses qualify, so the maker's compatibility chart is the only safe guide. We name no model here, because compatibility is specific to each lens and camera.

Converter, longer lens or crop?

You have three ways to get closer. Compare them honestly:

If your camera has plenty of resolution, cropping may be enough for casual use. A converter helps when you want the framing in the camera and your lens leaves aperture to spare. A longer lens makes sense if you shoot in dim light often. Our wildlife gear guide and bird photography settings show how reach and shutter speed interact, and renting versus buying helps if a long lens is a one-off need.

Test it before you rely on it

Once a converter arrives, check it while the return window is open. Mount the lens and converter on the camera, then work through a short routine:

1. Confirm the camera recognizes the combination. It should still report a lens, and the aperture readout should make sense.
2. Test autofocus in bright and dim light. A combination that focuses outdoors may hunt indoors.
3. Shoot the same distant subject with and without the converter, framed the same way, and compare the sharpness on a computer screen at full size.
4. Check the corners and the edges, where flaws from the lens are easiest to see.
5. Keep the setup steady. A tripod or a fast shutter speed shows the real quality, not shake.

If the combination disappoints, send it back. A converter that does not suit your lens is just extra weight in the bag.

Buying used

Teleconverters are small and sold used often. Check the glass for haze, scratches and fungus, test the electrical contacts, and confirm the lens and camera compatibility before you pay. If the seller cannot say which lenses it fits, skip it. Return terms matter here, as our used gear guide explains.

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