A teleconverter multiplies your focal length, costs you light, and only fits a short list of lenses. Before you buy one, you need to answer three questions: does it physically mount on my lens, what aperture am I left with, and does my camera still autofocus there. This page answers all three.
What it costs you in light
The arithmetic is fixed and there is no way around it. A 1.4x costs one stop. A 2x costs two.
| Your lens | With 1.4x | With 2x |
|---|---|---|
| f/2.8 | f/4 | f/5.6 |
| f/4 | f/5.6 | f/8 |
| f/4.5 | f/6.3 | f/9 |
| f/5.6 | f/8 | f/11 |
| f/6.3 | f/9 | f/13 |
| f/7.1 | f/10 | f/14 |
This is why teleconverters pair well with fast primes and poorly with slow zooms. A 2x on an f/2.8 leaves you at f/5.6, which is workable. A 2x on an f/6.3 zoom leaves you at f/13, which is a daylight-only proposition.
Sony FE: which lenses accept the SEL14TC and SEL20TC
FE 70-200mm F2.8 GM OSS, FE 70-200mm F2.8 GM OSS II, FE 100-400mm F4.5-5.6 GM OSS, FE 200-600mm F5.6-6.3 G OSS, FE 300mm F2.8 GM OSS, FE 400mm F2.8 GM OSS, FE 600mm F4 GM OSS.
That is the whole list. Sony teleconverters do not mount on other FE lenses, and they do not work on Sigma or Tamron glass. Sony adds lenses to this list as new telephotos launch, so check Sony’s compatibility page for anything released recently.
Nikon Z: TC-1.4x and TC-2.0x compatibility
Per Nikon’s own documentation: Z 70-180mm f/2.8, Z 70-200mm f/2.8 VR S, Z 100-400mm f/4.5-5.6 VR S, Z 180-600mm f/5.6-6.3 VR, Z 400mm f/2.8 TC VR S, Z 400mm f/4.5 VR S, Z 600mm f/4 TC VR S, Z 800mm f/6.3 VR S.
Nikon adds to this list over time, so a lens released after this page was written may well be supported. Nikon also warns directly that with a teleconverter fitted, the camera may fail to autofocus or the focus indicator may flicker depending on subject, light and focus point.
Note that the 400mm f/2.8 TC and 600mm f/4 TC already contain a built-in 1.4x you engage with a switch. You can stack an external converter on top of that, but you are paying the aperture cost twice.
Canon RF: the 100-500mm restriction you need to know about
Both the Extender RF 1.4x and RF 2x mount on the RF 100-500mm F4.5-7.1 L IS USM, but only within the 300-500mm part of the zoom range. You have to extend the lens to 300mm before the extender will attach, and once it is on, the zoom ring is physically limited to that range. The reason is clearance: at shorter focal lengths the extender’s protruding element would contact the lens’s rear group.
So with a 1.4x your 100-500mm becomes a 420-700mm, not a 140-700mm. With a 2x it becomes a 600-1000mm. You are not losing image quality by doing this, you are losing the wide end of the zoom entirely, and people are regularly surprised by it after purchase.
Canon’s big-white RF telephotos are designed around the extenders and carry no such restriction. Check Canon’s compatibility list for your specific lens.
The autofocus question
The old rule was that phase-detect autofocus died at f/8, which was a real limitation of DSLRs with dedicated AF sensors under a mirror. Modern on-sensor phase detection is far more tolerant, and reviewers routinely report working autofocus at effective apertures well past f/8.
What does degrade is reliability rather than capability. Autofocus meters through the lens at maximum aperture, so a dimmer view gives subject-detection less to work with. Expect a lower hit rate in poor light rather than an outright failure to focus.
When a teleconverter is the wrong answer
If your lens is already f/6.3 at the long end, a 2x puts you at f/13 and you have bought a daylight-only lens. In that situation a longer lens or simply moving closer will serve you better. Teleconverters reward fast glass and punish slow glass.
Compatibility verified against manufacturer documentation as of August 2026. Manufacturers extend these lists as new lenses launch — check the maker’s own compatibility page for recent releases.
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