I bought a 100-400 way back in 2005 and it has been on countless safaris since. Used on 2 x 1D, 7D and 1Dx. Never had an issue with dust or anything else. I did actually sell it this year when I bought the new Sigma Sport 120-300. If the mk 2 version eventually appears, I imagine ordering that but in the meantime, I might just buy another used example as it was so convenient. I have a 70-200/II plus converters but there is something nice about that old lump of a lens.
Interesting you should mention the Sigma. How does it play on full frame with teleconverters? Have you used with any ie Canon/Sigma? Please tell.
i read that the new sigma 120-300 does not work well with the sigma converters but have not tried them. i have tried the kenko 300's and the canon iii's. both the 1.4x tc's work well without issue. the kenko/promaster 2x pro af is fast and the iq is good but it overexposes by+1 ev so thats a hassle to compensate for it when you are changing modes and when you take it on and off. the canon 2xiii is a bit slower but seems to have more accurate af and the iq is just as good or better than the kenko.
i have used the lens and tc's on both a 6d and a 70d with good results. its a really versatile lens but i think its better for wildlife on a crop body. at least for small and distant animals and birds in decent light.
it may not be monstrous but its pretty big and its heavy (7 1/2 lbs). if you are going to get it then get the usb dock as well. it allows you to customize the af speed, focus limits, is behavior, ad af tuning.
Thanks, it's good to know the Canon TC's physically fit on the Sigma and are probably the best option I/Q wise. I have a Canon 1.4 II so not the newest iteration. Not sure if I will eventually go this path but it's best practice to be well informed beforehand
5D3, 5D2, Sony α6000 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 70-300L, 100-400L | E-mount: SY12 f/2, Ʃ19 & 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses.