The 600mm f/11 is a viable option not just something to be 'settled for' by people who wanted more
easy to use for a 600mm
no diaphragm to stop down more
no rotating tripod ring
horizontal only tripod mount
The tendency for reviewers and 'experts' is to point out that the 600mm f/11 is not as long as the 800 and not as fast as the big and expensive EF options. For those of us for whom price is a consideration, The $ five digit glass simply was not an option. The true cost of a lens like that should have to include the tripod (suitable for an 8x10 view camera) and salary for an assistant to carry the thing for you. The f/11 lenses allow you to have the thing ready to go with an absolute minimum of hassle.
The 600mm is not just a little brother for the 800mm version but a decent and practical option. Yes, I have encountered shots where the 800.. would have been nice but I have also taken shots that would have required me to back up with a lens that long. With prime lenses we zoom with our feet. Bigger is not always better. This situation may soon improve with the promised arrival of the Canon R7 APS-C body bringing the 'benefits' of the crop factor to our full line of RF lenses. The pixel density of the R7 will be greater than any other RF mount option. The 32.5MP crop sensor would require a full frame camera to have over 73MP to place as many pixels on that distant bird so a lens like the 600 will gain true useful gain for those shots where we just can't get close enough without requiring use of a converter that cost precious stops of light intensity. F/11, I can deal with; f/22 is pushing it a mite. While it might seem contradictory, I would not might having the option of smaller apertures for increased depth of field BUT I am glad Canon did not add weight and expense doing this. The secret of getting good results with this lens is a slight modification of the old rule: "f/8 f/11 and be there!" Make pictures while the sun shines. The high ISO performance of my RP up to 12800 makes me willing to put up with the speed limitation.
The feature of the lens I like the least is that collapsible tube that allows compact storage but I feel would have been better employed giving us a proper rotating tripod ring that would allow leveling and shooting verticals with ease. I am surprised some third party maker has not come out with a adapter that wraps around this useless tube and was grooved to accept a proper ring. I made one as a test that accepts the C(W)II from the old EF 70-300 f/4-5.6. I can't say I advise you to run out and void your warranty doing this but I do wish Canon would have allowed us a vertical option. I'm old fashioned and shoot stills, not video.
People criticize the f/11 lenses for not having a great minimum focusing distance. To them I say that at the MFD the frame is filled by a medium size woodpecker. If that is not good enough, you can add third party FR extension tubes (Canon chose not to make them but there are several options). Adding the most common beginner set of 31mm takes you down to about 12 feet. There are also longer tubes available that would get you into the 'too close' range which might be good for shooting those hornet headshots you have been afraid to try. Where there is a will, there is a way.
The 600mm f/11 is not the best lens if you can have only one and will not make the best photos under each and every circumstance. Is is a WHOLE lot better than sitting home wishing you had the money and strength to carry a cannon of standard specifications.
I attach a few shots made with the 600 and my RP. You can do better with your higher end RF bodies and greater photo skills. If not, don't blame the lens.
Great lens for the money, works for me, not disappointed so far.
Even produces a subtle bokeh
Not as weatherproof as more expensive lenses
Takes a 82mm filter, ouch!
I bought this lens as I wanted a 'long' lens for occasional use, and couldn't afford the price of an EF Prime lens, (over ten times more expensive). And this is only a my views on using it half a dozen times so far.
I was hoping this lens would be good, but not exceptional given it's price point. Having read several good reviews online it sounded worth the investment, and I'm not disappointed.
I use it on a EOS R5, (which I've not had that long), and am v impressed. I went to a local country park last week to try it out on some wildlife, which I've never shot before, and am delighted with it's performance, as hopefully the accompanying images show.
Just bear in mind a 600mm lens is not your average 'every day' lens, and like all long lenses will be susceptible to heat haze and general crap in the atmosphere.
What more can I say, if I remember I'll add some more comments in a month or two. 9.5 out of 10 from me.