Eric, good luck with that! A 500 mm lens is an absolute pig to hold still, so make sure you use a shutter speed of at least 1/500, if not 1/1000th.
In full sun, pointing to the trees sometimes shows over
1/2000 , F501 fastest shutter speed is 1/2000,
under 1/1000 i'll use a monopod , the bad thing of mirror is that has
a razor blade d.o.f. even at 10-20 meters of distance so one must be
careful with focusing .