A couple of people asked my thoughts on the Sony 200-600mm lens after using an adapted Sigma 150-600mm for the last 3 years. I've been using the Sony for a couple of months now so feel able to share my experiences.
Positives
Build quality, the 200-600 feels like an expensive and well made piece of equipment.
Image quality, they're not massively different but see stabilisation point. Very slightly sharper at 600mm wide open.
Image Stabilisation, one of my biggest positives, the lens works so well along with the in body IS on my A7iii that it allows me to shoot at lower shutter speeds and get sharper images.
Continuous AF, bird in flight was one genre than my adapted Sigma struggled with. I would get decent shots but the 'hit rate' of in focus shots was very low. The 200-600 copes much better with this and considering I am 'only' using an A7iii I can only imagine how well it works on more recent bodies.
Focus Acquisition, not generally a huge difference but faster at going from near to far and vice versa.
Zoom Ring, being able to go from 200-600 with such a short throw is very handy
Negatives
Manual Focus Override, this is massive for me and I am gutted that the 200-600 lens does not have this feature. Anyone that shoots small birds in and amongst the branches etc will know how important it is to be able to grab the MF ring to focus beyond all the foreground distractions and snap onto the bird with AF.
White Body, okay this is more of a personal taste thing but I really wish the lens was black and not white. I use a neoprene cover now so that is problem sorted.
Zoom Ring, I understand how people like being able to zoom with a single finger but for me it's way too easy to turn and often accidentally
Summary
Overall I am really pleased with my upgrade, the positives definitely outweigh the negatives and I feel like I am already getting more consistent with my bird photography and with the better continuous AF for in flight shots and the better IS for everything. The manual focus override feature not being present has really annoyed me as it's something I never even considered not being present on the lens, there are clunky ways around this like mapping a button to switch between MF/AF but nothing as natural and quick as grabbing the manual focus ring. All in all I am very happy with the lens and would give it a 9/10 and I look forward to Spring and using it much more going forward.