I had been observing a lot of chatter about the performance of 3rd party lenses with the new RF mount. In particular the comments that the very popular Sigma 150-600c has focusing issues on the RF mount. A review HERE by popular Australian photographer Duade Paton in a video where he found focusing issues was amplified, despite his clear statements on post with interactions with me that this is only apparent at close to minimum focusing distance.
So, I decided to take that combination to a gannet colony close to where I live. Without doubt, the lens, used with the Canon basic EF-RF adapter, was not as accurate as the native RF 100-500 lens, which is an amazing optic. However it performed acceptably - according to my statistics I got about 73% with a lock on the Sigma, and 84% lock with the RF 100-500 lens - the keeper rates are as much a function of the speed of these birds rocketing along and photographer error, so it was pretty good at getting the shots.
So, here are a few of images of my experience.
The bottom line is that the lens is capable of generating acceptable results for those who have this lens and are not updating to the RF native tele lenses yet.
A lesson one might take from your post is that the EOS R5 makes whatever lens one already owns look better and it is likely not necessary to buy a new lens. I admire your work.
I use "EF100-400mm f/4.5-5.6L IS II USM +1.4x III" and also the 2x III for a long focal length with the EOS R5. So far, the only non-Canon lens that I use with the EOS R5 is an adapted 45 year old Minolta 50mm from a film camera. I do not have any RF lenses. I also often photograph birds, so I am impressed by your photos. The EF100-400mm f/4.5-5.6L IS II USM also is good for closeups as well as distant subjects. I often use EF-S lenses as well. I use Canon DPP digital lens optimizer for the Canon lenses and for the Minolta lens I export a 16 bit TIFF from DPP on my iMac and use the GMIC plugin in gimp on my Linux machine for Richardson/Lucy deconvolution to remove small aperture diffraction blur.
Thanks. Your skill is greater than mine.
I was swinging the camera about wildly trying to track the eagle. If I had stopped down to F/13 there would have been less blur after correction for diffraction. Also, even over that short distance changes in air density caused distortion. Sometimes the 2x works and sometimes it doesn't. Here is one under less challenging conditions where it worked. Hand held, but from an automobile window to avoid scaring the bird. The water has the famous Oklahoma red dirt in it. Image is reduced to 50% to make it small enough to upload. Second is 100% crop and not reduced.
