Extender EF 2x III compatible with EF 100-300 f/5.6L on EOS R?

[rickmp001]

Hello,
Is the Canon Extender EF 2X III  compatible at all with the EF 100-300 F5.6L on a Canon EOS R body with Mount Adapter EF EOS-R? This is not on the compatibility list, but I was wondering if this combination would work, even if only in manual focus mode. Have been a Canon shooter since 1975 with an F-1 body (non-N variant). Thank you...

[Waddizzle]

How well does it work without the extender? That’s your answer. The lens released in 1987. It’s in the Canon archive. 

https://global.canon/en/c-museum/product/ef266.html 

It was designed for film cameras. Digital lenses use coatings on the internal elements to minimize light reflecting off the sensor back up into the lens body.  Thievrelections create haze in the image, similar to what you might see shooting through a window.  

As for the teleconverters, you might be better using a crop sensor body. 

[shadowsports]

Greetings ,

I would not recommend using this lens on a mirrorless body.  With or without a TC.  While adaptation may be possible, a lens this old is not going to be up to the communication standards or the performance required and offered by a mirrorless body.  Even in manual mode you'd be setting yourself up for disappointment if it worked.  

If you want to buy a budget 600 mm lens for use on a R series body I would recommend a.Sigma or Tamron 150-600, a RF 600mm f11, or an RF 200-800 for about $2k. if money is no object, the RF 600mm f4 is $15k, 

Don't go the Frankenstein route and hope for the best because you will be disappointed.

[johnrmoyer]

I do not have that lens, but I do use Extender EF 2X III. All of my older lenses work better on my EOS R5 than they did on older cameras. An old lens will not be worse and will likely be better than it was on the older camera, but still not as good as an expensive new lens. https://support.usa.canon.com/kb/s/article/ART173786 is a video about the manual focus assist guide in the EOS R. 

With my EOS R5 and adapter, I have used EF100-400mm f/4.5-5.6L IS II USM +2x III and it seems to me to work very well, better than on my EOS 80D.
I have also used a Kenko TELEPLUS HD C-AF 2X DGX and Vivitar SERIES 1 1.4X AF with older lenses.
https://www.rsok.com/~jrm/2021Sep08_birds_and_cats/2021sep02_bumblebee_IMG_3837c.html 
A Bumble Bee (Bombus pensylvanicus) was on a Zinnia in Norman, Oklahoma, United States on September 2, 2021. I made this photo with a very old lens as an experiment. I purchased the lens in 2011 and nearly wore it out. For this photo, it was attached to a newer camera body with an adapter with two telephoto extenders.

On a cloudy day, 

https://www.rsok.com/~jrm/2026Jun21_birds_and_cats/IMG_6045c_2026jun18_egret.html 

Snowy Egret (Egretta thula) at Lake Thunderbird in Norman, Oklahoma, United States on June 18, 2026

This might answer the specific question that you asked. 

https://www.dpreview.com/forums/threads/100mm-300mm-5-6l-with-extender.220412/ 

[deebatman316]

@rickmp001 I would take the advice from my colleagues @shadowsports & @Waddizzle that lens was Canon’s first EF L series lens. There are no lens correction profiles for it at all. Even from Canon’s own DPP photo editing software. The lens lacks IS and uses the original EOS AF Motor called AFD (Arc Form Drive) this AF motor was in production from 1987 to August 1991. It was phased out early on because it’s AF motor speed and the slow communication speed. These old lenses are classified under DPAF as F/8 lenses. Even though the lenses all have an aperture wider than F/8. These lenses also cannot AF & stop down at the same time. Since the communication speed is so slow. When the lenses are used on an EOS 35mm SLR, DSLR or adapted to the EOS R series. The FPS in Servo AF (formerly called AI Servo was locked down to 3-4 FPS). This is NOT a software limitation but a hardware one that CANNOT be changed. It may focus better on Mirrorless but the hardware is too limiting with that lens.

[shadowsports]

If I'm not mistaken, the EF100-300 (any) doesn't support a TC.  If you try to use it with an extension tube, you're just "frankensteining" the entire configuration more and losing Infinity focus.  

[ebiggs1]

"This is not on the compatibility list, but I was wondering if this combination would work, ..."

I have no idea since I have never tried that combo. One main reason is, I would never try that combo if I had the opportunity.  But that is my personal thoughts and the bottom line is what are you good with as a resulting image. If you like it and its seems OK then do it.

I went through the old lens to new and found out the images were not up to my standards. BTW, if you are adept at Photoshop or perhaps another editor you can make almost any image look pretty good I.E., the bumble bee.

I can say without hesitation the CA will be horrible. Again PS can help just too much effort needed to use that old stuff, IMHO.

[deebatman316]

@shadowsports you are 100% right about that. The EF Teleconverter was originally designed for the original EF 300mm F/2.8L USM lens from 1987. Also the 1.4x Teleconverter was dropped alongside that lens. The 2x Teleconverter was released in 1988.

[rickmp001]

Thank you for your reply. I am aware of the pitfalls of this lens, but for now it will suffice until I can justify funds for a more modern replacement.

Regards,

Rick

[rickmp001]

Thank you for your reply. I realize the lens has many deficiencies, but until I can justify spending on a more suitable replacement, I'll live with it.