RE: shooting the moon part II

[Robert A. Kelly]

I read somewhere that the formula for calculating maximum exposure time 
for shooting the moon is 250/ lens focal length = maximun speed in 
seconds. So if shooting with a  50mm lens would give a maximum exposure 
time of 5 seconds and a 500 mm lens would have a maximum exposure time 
of 1/2 or .5 second.  Shooting the moon with your 400 mm lens you 
should expose for no longer than .625 seconds, if you use a longer 
exposure time the movement of the moon will be apparent.

Cheers,
Bob