topic Re: Teleconverter Compatibility in EF & RF Lenses

EF 100-400 4.5-5.6 L IS USM lens Teleconverter Compatibility

DannyC71 — Sun, 15 Feb 2026 04:06:18 GMT

So I have the original EF 100-400 4.5-5.6 L IS USM lens, and already know that with the EF 2x Extender I can’t use autofocus because the maximum aperture is f/9. Does anyone know of a third party option that would still allow autofocus? The 400mm f/2.8 prime is not in the budget.

Re: Teleconverter Compatibility

shadowsports — Sat, 14 Feb 2026 04:27:09 GMT

Greetings,

What body or body's are you shooting with?

I'm not aware of any 3rd party 2x TC's that allow AF above f8. Why would you want to risk the performance?

Canon made an EF 300 f2.8 L that would do much better with 2x TC.

Maybe others will have recommendations.

Re: Teleconverter Compatibility

Peter — Sat, 14 Feb 2026 07:44:51 GMT

You will be able to use AF at f/9 with a mirrorless camera. Or a DSLR in Live view.

Re: Teleconverter Compatibility

normadel — Sat, 14 Feb 2026 08:20:55 GMT

The reason for autofocus not working is because of the light falloff caused by the distance increase from the lens to the sensor. It's the price you pay for wanting a teleconverter to increase focal length, instead of having a longer focal length lens.

Re: Teleconverter Compatibility

DannyC71 — Sat, 14 Feb 2026 15:34:50 GMT

I’m using it on a 90D. I know I’m losing a ton of light but was looking for a temporary solution until I can afford something better.

Re: Teleconverter Compatibility

shadowsports — Sat, 14 Feb 2026 15:50:33 GMT

Greetings,

I think this is one of those cases where I'd pony up and spend the cash. If a longer Canon lens is out of your reach, consider a Sigma or Tamron. 60-600, 150-600c or a Tamron 150-600 g2. These are half the price of the Canon EF 300 I recommended above. Any of them will pair nicely with your 90D.

Re: Teleconverter Compatibility

normadel — Sat, 14 Feb 2026 17:11:56 GMT

No such thing as a teleconverter that will amplify light. You cannot have what you desire.

Re: Teleconverter Compatibility

jrhoffman75 — Sat, 14 Feb 2026 17:16:21 GMT

With the high megapixels of the 90D and the image quality reduction of 2X converter, along with light loss and focus speed reduction, try just cropping in. Compare the results.

Re: Teleconverter Compatibility

DannyC71 — Sun, 15 Feb 2026 03:03:11 GMT

Years ago I had the Tamron G2 on a 6D Mark II and loved it, but when I went to the R7 the lens didn’t play well adapted to the mirrorless body. I went back to a DSLR and a Canon lens to simplify things, and now thinking trading in the 100-400 and going back to the Tamron may be the right choice.

Re: EF 100-400 4.5-5.6 L IS USM lens Teleconverter Compatibility

johnrmoyer — Sun, 15 Feb 2026 11:47:08 GMT

I used an EOS 80D with EF 70-300mm f/4-5.6 IS II USM and Vivitar SERIES 1 1.4X AF. The Vivitar does not correct the F Number or focal length, so the camera does not know it is there and will autofocus sometimes if the sun is bright enough.

Examples:

https://www.rsok.com/~jrm/2018Jan06_birds_and_cats/2018jan04_thunderbird_IMG_9888.html

Ducks at Lake Thunderbird State Park, Jan. 4, 2018, Oklahoma, USA

Camera Model Name	Canon EOS 80D
F Number	8.0
ISO	400
Shutter Speed Value	1/395
Focal Length	300.0 mm
Camera Temperature	16 C
Focus Distance Upper	inf
Focus Distance Lower	39.78 m
Lens ID	Canon EF 70-300mm f/4-5.6 IS II USM
Field Of View	4.4 deg
Hyperfocal Distance	581.96 m

The F stop and focal length above are incorrect because a Vivitar 1.4X teleconverter was used to make the photo. The exif data was not corrected by this teleconverter. The actual focal length would be the length listed times 1.4.

https://www.rsok.com/~jrm/2018Jan06_birds_and_cats/2018jan04_heron_IMG_9940c.html

Great Blue Heron (Ardea herodias) at Lake Thunderbird State Park, Jan. 4, 2018, Oklahoma, USA

Camera Model Name	Canon EOS 80D
F Number	7.1
ISO	800
Shutter Speed Value	1/395
Focal Length	300.0 mm
Camera Temperature	20 C
Focus Distance Upper	39.78 m
Focus Distance Lower	19.39 m
Lens ID	Canon EF 70-300mm f/4-5.6 IS II USM
Field Of View	4.4 deg
Hyperfocal Distance	655.73 m