The perfect lens IMO, at least for my needs, whether 28-70 FF or 42-105 in crop mode, stills or video.
Personally, I always shoot stills FF and use longer lenses for reach with say 24mp, but with something 60+ like some of the more recent Sony’s, I’d be quite happy to keep my lens sizes down and crop instead.
In fact, I am fairly sure that the Sony A7RV in crop mode is 26mp so a little bigger than the native 24mp FF sensors.
But the Sigma. Perfect size, weight, reach for me. I’m not much of a wider angle shooter and if so, I have a 20mm for that very limited (but still needed) requirement and prefer to shoot slightly longer lenses so 28 over 24, 40 over 35, 90/105 over 85 and rarely (but do need) anything over 150 and for that I have 180.
I shoot this combo crop mode all the time now as whilst I don’t need every bit of footage slow mo, some bits I do want to slow to 75% and other stuff to 50% and remembering to change back and forth between 25p and 50p when also shooting stills has caught me out too many times and the quality difference is marginal.
In fact, if you want better AF, shoot cropped.
Liked the 20-60 that came with my original S5, but really only used it as a day time wide, otherwise a bit slow for my needs and tastes, so sold it.
I’m an f4 day, 2.8 night, at their slowest kind of guy. I will generally shoot video wide open, but not always and stills generally the same or stopped down a bit, but a lot of my work can be low light and slower than f4 is a hard no from me.
That little Canon is a great lens. I had that adapter on my Fuji XT3 as a ‘75’ and it was a great cheap workhorse.
I do prefer primes in principle and would shoot them exclusively if it was practical for me to do so, but being able to be shooting at 180mm, rotate to 70mm and then flip (camera) to 40 and then 20, over 2 bodies, well it would need 4 bodies + 4 primes or a very handy assistant to do that otherwise!
But the Sigma 28-70mm f2.8 is a 💯% from me.
The Sigma f2 and f2.8 Contemporary primes are also A Grade as far as I am concerned with better build, feel, style and character over the Lumix f1.8’s plus have aperture rings and AF on/off switches on them.
It’s above 90mm where L Mount loses me…