|
That is normal practice so you are right, i think it will be that your star that you where checking wasn't in the middle of the FOV. its a simple fact that although the defocused star does infact fill 80-90% of the FOV its not centered itself.
Just so you can see what im saying go in a dark room with a torch.
Move the torch around your hand you will see the shadow of your hand moving with the torch. Even though the star is stationary your tube moves so the star comes in on different angles to your primary hence throwing the shadow to a different side.
|