Nesting eagles in Southeastern PA. To get a sharp image from a long distance my solution has been to use a Nikon 1 V1 with the FT-1 adapter which let me use a Nikon 300mm f/4 lens and a 1.4 adapter.  The gives the maximum reach for my system.  To get a sharp image also requires a very stable tripod and a remote trigger to minimize camera shake.