I’ve been watching/reading a lot of reviews and I’m not very sold on the lens. I’ve actually ordered a third party tripod collar and the EF to R adapter which will both likely take months. Once they arrive I’ll wait for a good sale then likely get the Tamron
Probably better to go with a canon 100-400mm mark I. The Tamron focus slower.
They appear to be discontinued here and stores only sell the II. If I was to go for a Canon 100-400mm I’d probably wait for the RF 100-400mm.
Agree - by all accounts the version 1 (used) is not a good option and from my experience owning the Tamron, it focuses very fast so I don’t know where that statement is coming from!
I think like many lenses when it first came out there may have been issues of copy variations, but the reviews much later after release seem really possible. Christopher Frosts review and Dustin Abbott’s were quite positive. As I’d use this lens for cityscapes, I found this one great too
https://www.lukecollinsphotography.com/tamron-100-400-lens-review/
Thanks - love the review - it makes me want to go back to Yosemite. I have not been there in 10 years. Hopefully the world will heal and and we can start traveling again.
Your thinking with regard to the RF, EF Version II, and Tamron are spot on. BTW, the Tamron has "USD" focusing which is similar to Canon USM - very fast. Still, I will be interested in seeing the Canon RF offering (later this year?).
Meanwhile, here are two more samples from this past weekend with the Tamron.

R6 + Tamron 100-400

R6 + Tamron 100-400
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http://www.pkimages.com