Image quality maintained with EF to RF converter?

[wabpro]

Currently I have multiple Canon EOS cameras with an EF mount. My main cameras are the 6D Mark II. I am looking at an R5 Mark II for the increased mp, among other things. I have a hoard of EF lenses. I am wondering about using the EF to RF converter.  My goto EF lenses are the 24-70 and 100 macro.  Is the image quality maintained with the converter and if so what will I notice between images with the 6D MKii and the R5? Has anyone done a side by side comparison between the DSLR and Mirrorless cameras using the converter?

[johnrmoyer]

All of my EF and EF-S lenses work better on my EOS R5 than on my EOS 80D. The adapter does not change image quality. Older lenses might not be able to focus as quickly or may require more time between shots when you hold down the shutter button. I have seen no reason for me to purchase any RF lenses so far, but maybe in the future.

EF-S lenses operate in 1.6x crop mode on the EOS R5 which is still nearly as many pixels as my EOS 80D.

A recent example: https://www.rsok.com/~jrm/2026Apr30_birds_and_cats/IMG_5771c_2026apr03_titmouse.html 

Tufted Titmouse (Baeolophus bicolor) in Norman, Oklahoma, United States on April 3, 2026

Camera Model Name	Canon EOS R5
Lens Model	EF100-400mm f/4.5-5.6L IS II USM +1.4x III
Focal Length	560 mm
Exposure Time	1/1250
ISO	2500
F Number	9.0
Camera Temperature	30 C
Measured EV	11.88
Measured EV 2	21.5
Focus Distance Upper	18.79 m
Focus Distance Lower	15.15 m
Artist	John Moyer

All of the edits in Canon DPP software

AngleAdj	0.5
WorkColorSpace	sRGB
WhiteBalanceAdj	Daylight
PictureStyle	Shot Settings
UnsharpMaskStrength	1.7
UnsharpMaskFineness	4
UnsharpMaskThreshold	5
ToneCurveOriginal	Yes
LuminanceNoiseReduction	5
ChrominanceNoiseReduction	5
DLOSetting	40
CropRotatedOriginalWidth	8239
CropRotatedOriginalHeight	5535
CropX	1508
CropY	956
CropWidth	4500
CropHeight	3000
CropRotation	0
CropAngle	0.5
CropOriginalWidth	8192
CropOriginalHeight	5464

Commands run on iMac, but would have been the same except for paths on Debian Linux:

exiftool -cameratemperature -description -keywords -imagesize -focallength -datetimeoriginal -ISO -rollangle  /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_5771.CR3 
exiftool -imagesize -datetimeoriginal -description -filename IMG_5771c*.[JHT][PI][FG]
exiftool -"description=Tufted Titmouse (Baeolophus bicolor) in Norman, Oklahoma, United States on April 3, 2026" IMG_5771c*.[JHT][PI][FG]
exiftool -sep ", " -"keywords=bird, Tufted Titmouse, Baeolophus bicolor, wildlife, wildlife photography, Oklahoma" IMG_5771c*.[JHT][PI][FG]
exiftool -Xmp:LicensorURL='https://www.rsok.com/copyright.html' -Xmp:LocationShownProvinceState='Oklahoma' -Xmp:LocationShownCountryName='United States' -State='Oklahoma' -Xmp:LocationShownCity='Norman' -Country='United States' -City='Norman' -copyrightnotice='Copyright John Moyer, all rights reserved.'  -copyright='Copyright John Moyer, all rights reserved.' -ICC_Profile'<='../sRGB_v4_ICC_preference.icc IMG_5771c*.[JT][IP][FG]
exiftool -tagsfromfile /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_5771.JPG -make -model -makernotes  IMG_5771c*.[JHT][PI][FG]

Commands used on machine running Debian free software after saving both 16 bit TIFF and JPEG from Canon DPP software (jpegli was built from the libjxl source code on this machine) :

exiftool -filename -imagesize -datetimeoriginal -description -keywords IMG_5771c*.[JHTj][PIp][FGg]
gm convert -verbose IMG_5771c.TIF[0] -resize "40%" -unsharp 0x1 -mattecolor black -frame 16x16 -font helvetica -fill white -font '/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf' -draw "text 4,1228 'Tufted Titmouse (Baeolophus bicolor) in Norman, Oklahoma, United States on April 3, 2026, Copyright http://www.rsok.com/~jrm/ All rights reserved.'" -depth 16  IMG_5771c_2026apr03_titmouse.png
cjpegli -v -q 96 --chroma_subsampling=444 -v IMG_5771c_2026apr03_titmouse.png IMG_5771c_2026apr03_titmouse.jpg
gm convert IMG_5771c.TIF[0] -depth 16 IMG_5771c2.png
cjpegli -v -q 96 --chroma_subsampling=444 -v IMG_5771c2.png IMG_5771c2.JPG
exiftool -tagsfromfile IMG_5771c.JPG -make -model -makernotes -description -keywords -xmp -iptc -state -city -country -iso -fnumber -exposuretime -lensmodel -exif:camera:all -"exif:time:all" -shutterspeedvalue -aperturevalue -artist -copyright IMG_5771c_2026apr03_titmouse.jpg  IMG_5771c2.JPG
gm compare -verbose -highlight-style assign -highlight-color purple -file IMG_5771_diff.jpeg  IMG_5771c.JPG IMG_5771c2.JPG

• IMG_5771.JPG is the straight out of camera JPG
• IMG_5771c.JPG is the image saved from Canon DPP software at the same time as a 16 bit TIF
• IMG_5771c2.JPG is the result of using jpegli on the 16 bit TIF
• IMG_5771_diff.jpeg is the difference between IMG_5771c.JPG and IMG_5771c2.JPG

• https://opensource.googleblog.com/2024/04/introducing-jpegli-new-jpeg-coding-library.html
• https://arxiv.org/abs/2403.18589 Users prefer Jpegli over same-sized libjpeg-turbo or MozJPEG
• https://arxiv.org/abs/2506.05987 The JPEG XL Image Coding System: History, Features, Coding Tools, D...

I was influenced by https://www.nature.com/articles/s41467-025-64679-2 to use 4:4:4 quantization instead of the 4:2:2 quantization done by DPP. "Ashraf, M., Chapiro, A. & Mantiuk, R.K. Resolution limit of the eye — how many pixels can we see?. Nat Commun 16, 9086 (2025). https://doi.org/10.1038/s41467-025-64679-2"

[LeeP]

The converter only increases the flange distance so that the lenses will focus correctly. The converter doesn't add anything optically.

[Waddizzle]

I agree with my esteemed colleague. The EF/RF mount adapter contains no optical elements, only electronics.  Because of the more advanced AF technology in R series bodies, you can expect sharper photos with almost any Canon L Series EF mount lens. Just bear in mind that every EF mount lens was designed for DSLR bodies with max frame rates of 12 fps or less.

[March411]

As others have already mentioned your EF lenses will work very well using the Canon EF/RF adapter. Some excellent information is available on which function may not operate to their full potential when using the adapter. The first link is EF lenses and burst rate. The second is a list of other compatibility reference materiel.

• Lenses Supporting Maximum High-Speed Continuous Shooting Speed  
• Supplemental Information - EF lens compatibility 

There are many of us that use or used EF lenses with the Canon adapter with excellent success.

• Lenses Supporting Maximum High-Speed Continuous Shooting Speed 
• Supplemental Information - EF lens compatibility (General listing) 

[LeeP]

Excellent information. Thank you for posting it.

Today I was shooting my daughter's credential graduation with my R100 and my 28-135 EF IS zoom via a Canon EF/RF converter. It worked fine. I got my shots under astoundingly dim light.

BUT

The lens is from 1998 and just doesn't seem as fast working as my RF lenses. I didn't miss a shot, but it felt like it was huffing and puffing a bit. I love it too much to replace--I probably need to--but the point is that the EF/RF converter is allowing me to use a lens coming up on 30 years old on a modern Canon mirrorless.

In addition to that lens, I have an Canon EF 85mm lens, an EF Lensbaby art lens, and an "el cheapo" fisheye lens, so the EF/RF converter has served me well.

I think it's a brilliant way to go mirrorless and not have to buy new lenses until you are ready if and when.

[I would kill to own Canon's fisheye zoom.]

[wabpro]

Thank you for all of the input, truly appreciated.