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Canon Teleconverter Compatibility

by Robert
(West Bath, Maine)

Extender For Canon

Extender For Canon

"I have a Canon Rebel XT with a 70-300 mm 1:4-5.6 IS USM lens. Is there a Canon teleconverter, either 1.4 or 2x that I can use with this camera/lens combination. I want to get up close and personal with birds at our feeder."


thanks for asking if a Canon teleconverter will work with your 70-300 f/4.5-5.6 lens and your Canon Rebel. No, it does not fit, according to a call made by Robert to You need to know two things about Canon camera/lens/extender combinations. We'll get to those in a second, but first to answer your question about the tele extender fit.

Canon teleconverters are built as EF lenses. That means they use full sized lens elements and provide a full size image circle-as opposed to Canon EF-S lenses. I wrote a fully detailed article on this that I think you will find it very helpful: Ef vs. EF-S.

Teleconverter Compatibility With The 70-300

Although the Canon teleconverters will successfully mount to EF lenses (like the Canon EF 70-200) there will be some loss of sharpness and some additional chromatic aberrations.

Canon EF 70-300mm f/4.5-5.6

This loss of image quality isn't necessarily significant enough for some Canon shooters to be a deal breaker, but you should be aware of it. It is definitely a subjective thing and you have to make a choice based on your own preferences.

I did my own geeky test of a 1.4X teleconverter II couple up with a 70-200 f/2.8 and you'll likely find this an interesting read as well: Teleconverter Sharpness Comparison.

I did my test using a high resolution 32 megapixel Canon 90D. With the 8 megapixel sensor of the Rebel XT you may not notice the change in image quality. You'd really have to test it and do your own side by side comparison. Also realize that there are 3 different versions of the 1.4x and 2.0x extenders, each later one having significant performance improvements.

Teleconverter Compatibility With The Rebel XT

Like all the Canon Rebels, the XT is an APS-C or "crop" camera. It will accept both EF and the smaller EF-S lenses. With the 1.6x crop factor of the Rebel, you'll get the same angle of view as if you were using a 112-480mm lens.

If you could add in a teleconverter with a magnification of 1.4, your lens will behave as if you have a 157-672mm lens on your camera. That's a SERIOUSLY POWERFUL amount of telephoto magnification. That would enable you to get very up close and personal for photographing birds.

Additionally, you lose 1 stop (or half of the light) with a 1.4x teleconverter and lose 2 stops (3/4 of the light) with a 2.0x teleconverter. Shooting in good light will be even more important and you may have to set your XT to a higher ISO setting to compensate for the reduced speed of your lens.

Finally, release you're going to lose auto-focusing capabilities as well. Although you have compatibility with the 70-300mm, your Rebel, and either the 1.4x or 2.0x canon teleconverters, you'll be focusing manually. With a decent tripod and shooting your bird feeder at a fixed distance, that shouldn't be a big issue either.

Feel free to comment back about what you decide to do. It will benefit all the readers of the Canon Geek blog.

I hope this helps,

p.s. I may be traveling along Rt. 1 through Bath on my way to a photo shoot in Acadia very soon.

p.p.s Some lenses will not accept teleconverters because of the protrusion on the teleconverters coming into contact with the lens elements on the camera end. This is particularly true with NON-telephoto focal length lenses.

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Tamron converter with no protruding elements
by: Anonymous

I have an older Tamron 1.4X C-AF1 MC4 teleconverter marked TAMRON-F that does not have protruding elements on the front end. It works with any Canon full frame lens or any non-Canon full or partial frame lens on any Canon AF camera. I bought it for my Canon 35mm camera and it still works on all Canon digital models. The only thing you can't do is put a Canon EF-S lens on it because Canon EF-S lenses stick out in the back and the Tamron converter is not designed to accept that protrusion. Non-Canon lenses will fit because they do not have that protrusion since they were also designed to fit Nikon cameras which never were designed to accept such a protrusion. Canon did it to save money on glass. Nikon & Pentax never did it. This was a dis-service to Canon owners since it prevents APS-C lenses being used on full frame cameras. Nikon never did it so they were never restricted in that area.

Newer off-brand teleconverters from Tamron and others stick out in the front so can only be used with telephoto lenses that can accommodate the front bulging elements of the converter. Mine doesn't stick out in the front or back and it is sharp.

The only converters that accept Canon EF-S lenses are off-brand converters that only have 3 elements and only work with Canon lenses because they have internal electronics to convert the apertures for exit data. My converter has no internal electronics. Whatever comes into the front of the converter is sent right through to the rear without any modifications to the exif. Thus if the lens is set to F8 it will be recorded as taken at f8, not the equivalent f11 with the converter. A small price to pay for full compatibility with so many off-brand APS-C lenses. All my tele zooms are either full frame Canon lenses or partial frame off-brand lenses so they all work with my old converter that was designed before digital cameras were invented with exif date to collect or Canon created their EFS-C design with the protruding elements on the rear of the lenses.

Converters and zooms
by: Anonymous

Just to add, I found the loss of quality using both the 1.4x and 2.0x converters with both the 70-200 and 100-400 mk2, made it impossible to get acceptable bird photos.
What has amazed me is the quality of photograph I get with my 1.4x convertor and my 600mm lens.

by: Robert

Do you know of any other vendor who might offer a teleconverter without the protuberance? no, It's probably inherent in the design.

Canon tech service
by: Anonymousrobert

"I took your advice and called Canon. Took three tries and 20 minutes on hold but finally reached a person. Explained the situation as I did here and got a one word answer, no. This lens, she said is not compatible with any canon teleconverter.

Bummer! Looking at the diagram of the version II of the 70-300mm lens looks like there might be enough space to fit the protrusion from the teleconverter. I know that Covid19 restrictions have drastically adjusted the hours and service level that many companies (including Canon's)

by: Robert

"Thank you for the detailed info. The canon compatibility lists always seem to omit my telephoto lens leaving me frustrated. I appreciate your hands on guidance. I’ll give you feedback when I make my purchase."

Robert, My concern with compatibility and your 70-300 is that the protrusion on the extender will hit the first lens element on the camera end of the 70-300, as I'm not sure of the clearance and its specific design of the lens elements. Your best bet on a super specific like this is to call Canon USA directly. Just be sure you can return the lens to the seller if I'm wrong.

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Author Bruce Lovelace
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Bruce Lovelace is the publisher of Canon Camera Geek. Read more about him on the About Page. He also publishes how to articles and camera gear reviews at the Photography Tips website.

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