06-09-2025 02:48 AM
I have recently purchased an R5 (mkI), and while I'm very happy with it, I'm noticing some issues with EF lenses. Yesterday I tried an EF 600mm f4 IS mkI, and while it did focus perfectly, the motor was very slow. When I tried the same lens on the owner's 1DX mkIII, it was quite fast. He said it requires largeer batteries to run the motor, but I have never heard of this before, is that true? I m planning to purchase an EF 600 mm f4 eventually, preferably mkII, but I need to know that it will work properly on my R5. Which of the lenses will have this kind of issue? How about the 400 mm f2.8 or the 500 mm f4 lenses, would any of them focus slowly on my R5?
I should say that I am using a third party EF-R adapter (Meike), but I have been told that it should make no difference as the electronics simply pass through.
Additionally, I have had the feeling that my EF 100-400 mm mkII is not working perfectly with the R5, specifically the image stabillization feels more shaky. I was expecting a more stable viewfinder with the IBIS of the R5, but that is not what I'm getting. I do still get sharp shots, but it feels like it takes a second longer for the IS to stabilize the lens on the R5 thhan it did on my 5D IV, have anybody else experienced this? Could it be because IS is always running on the R5 and it needs to adapt to a new angle once you lift it to your eye?
Cheers, Tobias
06-09-2025 03:22 AM
Do not assume that every Canon EF mount lens ever made is fully compatible with RF mount cameras with Dual Pixel AF sensors. This table is from the R5 User Guide
After Canon introduced Dual Pixel AF they introduced Mark II versions of nearly every L lens. They also introduced STM versions for most consumer lenses.
Are you using a tripod or monopod with the 100-400mm lens? Are you panning with it?
06-09-2025 03:37 AM
I don't understand how the autofocosing system should affect compatibility with lenses, unless of course there is a poralizing filter or similar involved. It may be naive, but I assume the lens simply delivers light and an image, and then the autofocusing system finds where contrast across pixels is highest? As far as I know, 1DXIII also has dual pixel AF?
I am however aware that the old lenses are not compatible with fast shooting rates. That is not my issue at all, but the speed of the motor itself. I don't know if I needed to fix a setting on the R5, I have heard of others using the first version 600 f4 IS on R5 with full compatibility except being limited to ~7fps.
I' usually using th e 100-400mm handheld. I'm panning now and then (rarely using the mode 2, although I know I should), but I mostly notice the shaky viewfinder when I am photographing something stationary.
06-09-2025 05:08 AM
“ I don't understand how the autofocosing system should affect compatibility with lenses, unless of course there is a poralizing filter or similar involved. It may be naive, but I assume the lens simply delivers light and an image, and then the autofocusing system finds where contrast across pixels is highest? As far as I know, 1DXIII also has dual pixel AF?
I am however aware that the old lenses are not compatible with fast shooting rates. That is not my issue at all, but the speed of the motor itself. “
Canon’s lens list is telling you that lenses not on the list are too slow.
06-09-2025 05:17 AM
Yes, of course. But I think specifically the aperture closing mechanism is too slow for high FPS. The compatibility list does say compatible with H+, not compatible with the camera. This is not the lens focusing motor itself being too slow, because it was much faster on the DSLR. Same lens, same day, I'm just looking for the reason it was moving at a slower pace on my camera. And maybe why people report that the lens works perfectly on R5, but not my R5... I was quite happy with the roughly 7fps I got with it, but not with the focusing speed.
06-09-2025 05:36 AM
Older Canon EF lenses were created for the cameras of the same time. In September 1999 the EF 600mm f/4L IS USM was a new lens. Canon's own DSLRs only arrived in the Spring of 2000.
Such old lenses were not designed for the high frame rates of modern cameras - the cameras of the time did not shoot that fast - and they AF used the technology of the time, plus larger ring type USM lenses needed more power to drive them. The aperture assembly was designed to be very consistent with exposure, but not to open and close particularly quickly as fps rates for film and early digital cameras was not so fast.
When the EOS-1D Mark IV DSLR camera was introduced at the end of 2009 there was a change to the AF communication algorithm, the camera could work with older lenses, but with the latest and subsequent lenses there was an AF speed improvement. The subsequent Mark II version of the super telephotos all supported that new faster communications and had aperture assemblies designed to operate more rapidly. Still some photographers found these lenses performed better on the EOS-1D series cameras due to the bigger more powerful batteries.
Moving forwards the RF 400mm F2.8L IS USM and RF 600mm F2.8L IS USM lenses take advantage of the larger power supply in the EOS R3 and EOS R1 cameras and offer an enhanced AF speed when used with those cameras.
The reality is that the camera tells the lens what to do, the lens internal processor and motors determine how fast that can be possible. This is where the limitations come from.
There are multiple reports in this forum of EF lens and RF camera compatibility issues when using 3rd party adapters. In all cases I can remember the problem disappears with Canon adapters.
06-09-2025 09:39 AM
One thing to note is that with DSLRs is that DPAF is NOT available during viewfinder shooting. Unlike Mirrorless cameras where it’s available during viewfinder and live view shooting. When using a DSLR camera during viewfinder shooting. The camera uses PDAF (Phase Detect Autofocus). The AF sensors are on the floor of the camera under the mirror. This system doesn’t exist in Mirrorless cameras at all. This older system relies on contrast. Or AF will not work unlike DPAF. Most older EF lenses were designed specifically for that system. Not DPAF because that didn’t exist. Also when using a DSLR in viewfinder mode. Not all of the AF points can be used with older lenses. The manual has lens groups. That show which lenses are fully compatible with all AF points and teleconverter combinations. Remember the oldest EF lenses still work on the newest DSLR cameras. When some of these lenses were released most cameras only had anywhere between 1 AF point to 9. That was till 1998 when the EOS 3 film body was released. That was the first camera to have the 45 point AF system found in the EOS-1V and later EOS-1D series cameras. It also brought F/8 AF too. In 1992 Canon switched from Arc Form Drive AF motor lenses to Micro Motor. Which this change Canon changed how AF and Aperture control worked. These older lenses AF and stop down sequentially instead of at the same time. So these lenses are limited to 3 fps when the camera is set to Servo AF. This didn’t affect USM lenses they were designed to do both actions at the same time. Also Canon first released USM lenses in 1987. But these lenses had a twist the focus ring was electronic like an STM. If the camera was set to Servo AF the focus ring is ignored. The focus ring isn’t directly connected to the focusing elements in the lens. All the focus ring is connected to is a digital encoder.
03/18/2025: New firmware updates are available.
EOS R5 Mark II - Version 1.0.3
02/20/2025: New firmware updates are available.
RF70-200mm F2.8 L IS USM Z - Version 1.0.6
RF24-105mm F2.8 L IS USM Z - Version 1.0.9
RF100-300mm F2.8 L IS USM - Version 1.0.8
RF50mm F1.4 L VCM - Version 1.0.2
RF24mm F1.4 L VCM - Version 1.0.3
01/27/2025: New firmware updates are available.
12/18/2024: New firmware updates are available.
EOS C300 Mark III - Version 1..0.9.1
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