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Compatibility of R5/6 and EF/EF-S lenses


Gentlemen: I'm considering upgrading from a Canon EOS 7D Mk2 to either an R5 or R6.

Will the following lenses work (be fully compatible) with either of the bodies?

Canon Macro Lens EF 100mm 1:2.8 L IS USM
Canon Zoom Lens EF 70-200mm 1:2.8 L IS II USM
Canon Zoom Lens EF 100-400mm 1:4.5-5:6 L IS USM
Canon Zoom Lens EF-S 10-25mm 1:3.5-4.5 USM
Canon Zoom Lens EF-S 17-55mm 1:2.8 IS USM
Canon Extender EF 2x III

If not what are my choices (upgrade the lens, firmware, adaptors)?

What else should I be aware of before investing?

Things I am hoping to achieve: Autofocus when using 100-400 and the extender, faster focus on subjects (especially for bird photography).

Thanks and kind regards,




I am not in the mirrorless game yet but my understanding is form my buds that have gone to the dark side tell me the EF lenses work well. However, your EF-S lens were designed for a smaller sensor so they will not be as good. But they still should work just you won't get a full sensor image. Someone that has actually done it might answer more thoroughly.

EOS 1DX and 1D Mk IV and less lenses then before!


Thanks @ebiggs1.

Is there a place when I can find pictures of the same subject taken on R5/6 with various lenses (RF, EF, EF-S)?

I have no idea what to expect.

Pictures made with EOS R5 and EF and EF-S lenses are at

I have found that all of my old EF and EF-S lenses work better with my EOS R5 than with my previous cameras.

The EF-S lenses are cropped by 1.6x to about 17 megapixels which is a few less than my EOS 80D but more than my 11 year old Rebel.

As an extreme example, this was hand held and auto focused:

F Number16.0
Shutter Speed Value1/395
Focal Length700.0 mm
Lens IDCanon EF-S 55-250mm f/4-5.6 IS
Lens IDVivitar SERIES 1 1.4X AF


Bumblebee on ZinniaBumblebee on Zinnia


That's what I was looking for and wanted to read and see first hand..I feel much better that I can still put the perfectly fine lenses I have to good use with an upgrade to the body (except for the weight)

What kenko product was that? I have the extension tubes - forgot to add that to the list. Will they work with the adaptor?

I do not have extension tubes. The Canon extenders will not work with the EF-S lens which is why I have the Kenko 2x extender. The bumblebee was two cheap third party extenders stacked and wide open at F/16. I often use EF100-400mm f/4.5-5.6L IS II USM +2x III which autofocuses well on EOS R5. Sometimes I use 1.6x crop mode with the 2x extender because it does quicker and better eye detection on birds. When using the Kenko extender, I have to turn off image stabilization because it gets the focal length wrong.

Here is an example with the EF 2x III extender:



Assuming that you are using a Canon mount adapter, all of the Canon lenses you listed will work just as well on an R5 or R6.  The main difference will be the EF lenses will offer a wider angle of view.  

The EF-S will offer the same angle of view as your 7D2, except the end result will not have the full resolution of the image sensor.  The camera will automatically enter a “crop mode”, which only uses a center portion of the sensor that is approximately the size of an APS-C sensor.

Food for Thought.  I do not own a Canon MILC body.  I do own a 5Dsr, which also has a crop mode for use with full frame lenses.  The RAW files it captures in crop mode are the same size as files when it is not in crop mode.  

What happens is not all that different than changing the Aspect Ratio of your images.  The EXIF tells editing apps how to display the image.  The original 3:2 RAW image is what gets stored.  

I suspect the same behavior from the MILC bodies when they automatically crop images when an EF-S lens is used.  You will get the same size RAW file, but I would expect JPG files to be cropped in resolution resulting in much smaller files.

"The right mouse button is your friend."

Thanks @Waddizzle

When the camera enters into crop mode (with EF-S) lens, does that mean the raw file size will be correspondingly smaller? Or only when I convert it to JPEG? I'm mostly concerned about the R5...45mp files.

Can  you please elaborate on this "crop mode" behaviour?

Will the quality of image captured with EF-S lens on R5/6 be significantly better (sharper etc..) than that captured with 7DMk2 with the same lens and same conditions? What about AF behavior and speed and IS behavior?

One of the main reason to upgrade's becoming increasingly hard to hand hold the large zoom lenses and the heavy I'm hoping the weight and IS of R5/6 will help somewhat...

For the aspect ratio crops, the EOS R5 behaves as @Waddizzle described. For the 1.6x crop set in a menu on the camera or set automatically because an EF-S lens is attached, the CR3 raw file is much smaller.
Not cropped: "

IMG_8025.CR351.7 MB4/29/22, 5:56:57 AM


1.6x crop set in menu: "

IMG_8023.CR321.0 MB4/29/22, 5:56:25 AM


The one that is not cropped by 1.6x is because the bird was closer to the road and I needed a wider field of view and did not want to tell the bird to wait while I zoomed or changed lenses. I made the photo hand held from a car window. I have C3 set to the 1.6x crop because I use it frequently. The image stabilization is amazing. I set the IS switch on the lens to mode 3.

I am 73 years old and still can hold this lens.

Version one of the 100-400 has a reputation for not auto focusing as quickly as version two and for not having such good image stabilization.

The 1.6x crop with the EOS R5 makes a much smaller raw file. The other aspect ratio crops are as you describe.


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