I am one of the lucky ones since most of my shooting is with 600mm Canon with 1.4 extender with a 7D . That puts it at 840mm, most of my back yard birds are use to me and comfortable at about 25 feet. At that range they fill the frame pretty good. But for posting I usually re-size my photos to 6inch by..and up the dpi to 300. I only do this as a hobby and still learning and having a fun. BIF is my big challenge,but still learning and studying many books and on line stuff. I don't mind cropping as long as the quality of the image is not comprised.