You asked
Best telephoto lens for the sony a7s?
For telephoto on the a7S, I'd start with the Sony FE 70-200mm f/2.8 GM OSS II. It's fast, sharp, and handles portraits and sport as well as distant subjects. If you need more reach for wildlife, the Sony FE 200-600mm f/5.6-6.3 G OSS gets you much closer to the action. For fast long reach and you don't mind the size, the Sigma 300-600mm f/4 DG OS Sports is the serious option.
The a7S has no in-body stabilisation, so pick a stabilised lens like these three. Its 12.2-megapixel sensor also means you can't crop far, so get the reach from the lens, not from cropping later.
For more on choosing, see wildlife and sport.
Written by Claude from this site's pages.