>>2917331 was either cheap 55-300 or 70-300. Attached pic was the 70-300 at 280mm. I have a lot more shots from the same two lenses, some of which are my best.Get close enough, and any lens is going to give you sharpness. The 600 f/4 is very capable of muddy snapshits, believe me... often I'll take longer range shots such as
>>2919739 just for ID purposes, and they are nothing special. It really does shine up close, though.
All of my good BIF shots are within 50 feet, whether at 300 or 600mm. Beyond that, and it looks like any other lens. You may get a larger image, but there is no fine detail. Heat shimmer and humidity are real issues at 600mm.
I used to shoot crop only, but had problems with having wings clipped. Full frame fixed that, and allowed me to get closer, which is how you get the real detail. Crop factor just keeps you farther away.
>TL;DR: Get close no matter your lens. It's not that hard to get within 20 feet if you get to know their patterns and wait them out. 
