I too purchased the RF 100-500mm lens from Amazon a couple of moths ago, but did not have the time to test it at the local sled dog races in the interior of Alaska. I finally mounted the lens on my R6 last week and spent a couple of hours outdoors photographing the mushers and dogs. The ambient temperature was around 2 degrees F.
I havent' experinced the problems mentioned above with this lens, but so far I am am not impressed by it, and feel that instead of this lens I should have purchased the EF 100-400mm L (version II) plus a 1.4x extender, simply because this lens has been proven as a workhorse. RF lenses with IS plus IBIS working together are supposed to be superior to EF with IS and IBIS. But is this true in real life situations?
Since I am not en expert, all I can do is to tell you how the RF 100-500 lens performed for me at the sled dog races compared to the EF 135mm L USM (this lens does not have IS). The R6's image stabilization was turned on, and so auto ISO. I left the lens aperture to its default. I zommed the lens to 200mm, all the way to 500mm depending on the shot I was taking at the moment. The ISO chosen by the R6 was 100, and the shutter speed remained around 400s all the way through.
Yes, I could have changed the shutter speed to 500s or even 800s, but I wanted to test the lens alllowing the R6 to do its work automatically on Av mode. When looking at the RAW images at home, they were not as sharp as I expected from a L lens. These images look soft to me, specially the dogs eyes (I set the R6 for animals, eyes focus, and to track the lead dogs).
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The second day of the races I decided to used my trusted EF 135mm f/2 L "adapted" to the R6 (remember, not IS on this les). I set the aperture to f/6.5, and preceeded to shootway. The shutter speed stayed around 500s thoughout, and the images are quite sharp compared to the ones above (some cropped to 400%). I can only assume that they are sharper because of the faster shutter speed (?). Camera was handheld.
I will continue testing the 100-500mm lens, but I already know that I am not using it to photograph the sled dog races in the interior of Alaska. For this I will continue using my very of and reliable EF 200mm f/2.8 L (black color with a red ring at the front and no IS), and the 135 f/2 L. The images resulting from my 7D and these two lenses can be cropped over 300% and still look very sharp. Not so the photos I just took usig the RF 100-500. In fact, 100% crop was not good enough for me.
I will return to post some photos in the near future.
By the way, I have already registered both the R6 and the RF 100-500mm lens, but they still don't show in my list of Canon products I own.
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Edited on March 09, 2021
I had to come back and edit as a token of apology to all who have read my coments about my first impressions of the canon RF 100-500mm.
My apology is as folllows: The main problem relating to the performance of this lens relates to user error, not the lens itself. in this case I forgot to switch the lens IS from the number 1 position (stationaty subjects) to number 2 (moving subjects), so only IBISn was active when I was photgraphing the sled dog races. The lens performe quite well when zoomed to perhaps 200-250mm, and not as well when zoomed past that because its aperture was then greatly reduced to perhaps f/7.
I have a lot of testing to do in the near future, but at least the lens operation in relatively cold weather for a period of two or three hours went well. The ambient temperature was from just below zero F. to perhaps a maximum of 10 degrees F.
