Originally posted by MossyRocks
I also don't know anything about the rear drop in filter system which is what I have the most curiosity about so that would be helpful so I don't screw things up as I will be using a filter at night when shooting astro shots.
I don't own such nice beast, but i would if I could... but if this is like the FA* 250-600, the rear drop-in filter is part of the optical formula, and it may get worst if you remove it.
Originally posted by stihlmania
It is a wonderful Astro lens.....
I agree, if I was ablt to get this (single frame) shot below with the Pentax K-1 + SMC Pentax-FA* 250-600mm f5.6 ED [IF] @ 600mm
30s, f6.3, ISO 6400
the 400mm with 2 more stops will sure be a winner!
Galaxie d'Andromède / Andromeda Galaxy (M31, NGC 224)