I have a EOS rp and yes I know it is not the best wildlife camera, but It is just a hobby not my life's work. So the real question is which lens to buy? is the extra reach worth the sacrifice of build/quality?
i don't have the canon one but i do have the sigma 100-400mm c and the sigma 150-600mm c to which i use on my M50 with canon ef to efm adapter. while i can't offer a comparison to the canon lens what might b of use is the weight and size difference between the sigma 100-400mm and 150-600mm, it may have some bearing on the canon 100-400 vrs the two bigger lenses. for me the 100-400mm c sigma is an easy walkaround lens fitting eaisly into y regular shoulder bag with the M50 attatched and with the lens hood open, the 150-600mm is a fair bit longer so and a bit heavier making it a tripod lens for me the extra reach from the lens makes a big difference on the moon and planets, its just that extra bit of reach what takes them from nice moon images to images you can work with to put names to craters and get to know the surface. as yet i havent taken the 150-600mm out birding, its always been easier to grab the 'smaller' 100-400mm, now that the weather is getting a bit colder i'm more likely to be dressed for lugging a bigger lens about (normally dress and heels for photography) so it will be getting a bit more wild life action. something to search for honest opinions on rather than brand snobbery are the auto focus speeds of the cheaper lenses, some say they are not as fast as the canon ones, i giuss it depends on the camera too. the build quality has been good on the 100-400mm and the other sigma lenses i have like the art ones etc, the quality of the images are very good but i'm just a jpeg shooter and i also dont have the canon to refer to not terribly helpful but as a user of the lenses they been good to me, both work well with the canon mkIII teleconverters, 1.4x and 2x they even focus correctly on jupiter with two 2x converters stacked
I disagree, This is very helpful I know the sigma is quite a bit heavier and I need to use and EF/RF adapter. My big concern is the extra reach. It may or may not be worth it due to the other shortcomings
Wildlife comes in all sizes. What are you trying to shoot, and how close can you get to this wildlife? Gary
You will likely want a decent amount of zoom to reach birds at a distance. In your RF mount the RF 24–240mm F4–6.3 IS USM is the cheaper option and will cover everything from wide shots to long zoom. It will do a lot of things well but has its limits. (jack of all trades, master of none basically) You can get a Canon RF 70-200mm f/2.8L IS USM which is very a nice fast pro level zoom but that will cost $2800, it will however easily allow* you to add a 1.4 or 2.x extender and make the zoom reach to 300 or 400. There are also other options of adapting EF lenses from Canon or even Sigma / Tamron. Just a few option to get you thinking but I recommend at least try to hit 200mm if not longer if you want to photograph birds, but it really depends how close you can get to them. Adapting EF lenses will probably be a little cheaper and give you many more lenses to pick from.
hmm, in the woods, whats the available light like? i solved my very low light night time fox hunting with a sigma 105mm ƒ1.4 as i was only shooting with street ambient light, i doubt you would need to go thet extreme during the day time. going back to the original question, i don't think you are loosing out on quality, the big one is the aperture speed really when it comes to long wildlife, esp if you shooting in the woods, the lower the iso the cleaner your image, have you considered a faster 400mm prime? i don't know you budget, i think my ideal wild life zoom lens would be a 400mm-600mm or 300mm to 600mm and as fast as you could get it with out it being crazy heavy which is the canon 100-400mm lens you are comparing btw?