I am a bit new to using longer lenses for bird photography, Realistically how much can i crop an image before IQ will suffer beyond acceptable amounts ?
I am using a Canon 60d with either a 100-400 5.6 or my new 300 2.8 ii. with and without a 1.4 TC iii.
maybe a better way to ask would be how much of the initial shot should fill the frame, ?


