I've used my EF 100-400 with an RF adapter. It's good but as someone older, this RF lens is light, compact, and is optically sound for my purposes. I also own a 150-600 Sigma which usually needs a pod to hold steady and I've missed more shots than I've captured with it. This RF 100-400 is great for me; it so easy to pan while shooting birds in flight!

I think the picture quality is some times soft with using and extender, but not to the point it is overly noticeable, or makes picture unacceptable. Doubles your lens and is compatible with EF mounts. In the photos attached the first two were taken with a 5D mark III 100 - 400 zoom lens with 2x adapter for 800 MM the third was with a 5D S R 100 - 400 mm zoom lens at 400 mm no 2x adaptor

I read a good review on the RF 100-400 IS lens and, having already experienced the high quality of the RF 600, decided to give it a try. My initial impression is that this lens will be producing some fine quality images with it's stabilization and lighter weight compared to my EF 75-300 L, especially when chasing butterflies without a tripod. The RF 100-400 can focus much closer to a subject compared to the RF 600 and is a welcome addition to my collection. Thanks

I use this with 400 and 600 mm lens and it works great.

Returned because I put it on my 100-400 4.5 and lost too many stops.

I'd originally planned to get the RF 100-500 mm L lens, but it costs nearly $3,000. At well under 20 percent of that price, this is a great value. Sure, it's a little slower and only 400 mm at most, but it's a lot lighter and takes very good pictures. I haven't compared it directly against that L lens, but pictures are comparable to or slightly better than the (e.g.) Tamron 150-600 mm G2 EF, although with less reach (but a delight to carry around). I'm very glad that I bought this (100-400 mm) lens.

Download 100 movies and is only 40 % full could possibly download 400 more movies

I’ve been known to be a Canon L lens snob. I picked up this lens for my daughter’s kit but decided to test it during a local soccer game. Besides losing a 100mm of range from my Canon 100-400 L II lens, I noticed no significant visual difference in the photos compared to the significantly more expensive L. In the end, I post process every pic anyway so they only thing that matters to me is sharpness, focus speed and accuracy. This little lens does the trick in all those areas and is great for video. In fact, I’m keeping it and selling the 100-400. It is a very nice lens and I highly recommend it.