u/Fair-Bother2197

What's the most overall great telephoto lens for a Sony aps c camera like A6400 that I can pair with my sigma 18-50mm f2.8? I have noticed that the zoom lenses usually recommended are maximum aperture at f/4.5 Is that just how it is? Also what are the most common prime lenses focal lengths in the telephoto range just in case I go the prime lens path instead? But I really would like something versatile, especially since I'm a new beginner.

The posts that I post on Instagram with the original resolution and full file size plus full jpeg quality look noticeably sharper than when I resize to 1080. So I don't get the whole thing with people saying resizing is a must... Any reflections/ observations on this? I mean Instagram compresses the living fuck out of all my work no matter if I resize or not, but when I resize it stays the same or often worse than using full resolution. What. The. Hell.