Posted this on Reddit as well but wanted to hear the opinions on this site as well-
Currently have an EOS R and an older EF 70-200 F4 IS that I use with the adapter. I also have a 1.4x and 2x extender as needed. I am happy with the Image Quality, but the lens is starting to show it's age and the amount of work I have to do to get the adapter- then extender, then lens, then mounting it has made me lose out on some time-sensitive shots.
The RF100-400 is the perfect focal range, as my other lens is the 24-105 F4- but I worry that ill see a reduction in IQ if making the switch- not all that worried about it being a slower lens. I am hoping someone has made the same move and can give me some feedback.
Back in the day, the EF 70-200 F4L IS USM lived on my 5D MKII and 6D and captured many a landscape. It was a great design for its day. When I switched to R, I kept using it for a while, but eventually replacing it with the RF 70-200 4L IS and the RF 100-400. I wasn’t a fan of using the adapter, and the old ring-USM was a bit jerky for video. The RF 70-200 4L IS is much smaller—almost silly small in comparison—and perhaps a notch up in IQ. And the nano USM is more surefooted and smoother for video. It doesn't work with extenders. The RF 100-400 is built really cheap, but the nano USM is fast, and the IQ is surprisingly excellent. It's not as flare resistant as the EF 100-400L II, but IQ is only a notch behind it, and it's much easier to travel and hike with.
I saw little—if any—reduction in IQ with the RF 100-400 compared with the old EF 70-200 F4L IS USM. Its main drawbacks are F8 max at 400mm, so a lens for good light only, no weather sealing, and not very tough. RF 100-400 and R6 MK II:
Originally I was worried about the max aperture of F8 until I realized at that focal length using my 2x extender on my F4- the max is still F8. Thank you so much for the response and feedback
I have the RF 100-400 and it’s super light for hiking. It does feel cheaply made but if you can find the right deal I think it’s worth it. I grabbed one off the canon refurbished sale for $399 last year. It always sells out quick when refurbished lists them, but maybe a good Black Friday sale is coming up. I used it at an air show and was quite happy with the results.
I've had all four versions of EF and RF 70-200/4s and still have 3 of the them. None of the EFs are very good with a 2x and even with a 1.4x there is degradation, although the 30MP bodies are fine with the 1.4x. So you should be happy with the 100-400/8 being better at the long end. I'd still keep the 70-200/4 IS if it works well. That is a still a very good lens at 30MP without any TCs.
I have both (also an older non IS f/4 L) although not with converters; They are close enough that it's preference IMO. I find that the IQ nod goes to the EF-L by a reasonable measure and I love that it's not an extended zoom. The 100-400 is far better for travel (light and not eye catching white) and the IS is significantly better. It's also obviously better between 200 and 400mm I don't find the f/8 a hindrance for the most part but it's noticeable against an f/4 zoom.
I don't find the f/8 a hindrance for the most part but it's noticeable against an f/4 zoom.