Silly question?

[multiweb]

I'm not much of an observer but I was start testing my C11 tonight after some major surgery and then I got carried away and spent 2 hours with my daughter looking around the moon, saturn and other stuff. The moon details were ultra sharp. Saturn was very clear too. I noticed that when jumping from the moon to saturn I had to refocus and vice versa. The collimation was spot on and it wasn't mirror flop either but because saturn is side on right now it was very obvious I could see two lines for the ring until re-focusing. The focus point was extremely tight and very obvious but clearly different for the two. Is this normal? I thought whether you looked at a star or a planet or the moon you still focused to the same point (infinity)? :question:

[DavidU]

That's a good question. I find my refractor does need a slight tweek between the Moon and a star.

[avandonk]

Your eye is compensating without any apparent effort on your part as both these objects are so dissimilar in extent and brightness. Bert

[multiweb]

Thanls for the clarification Bert - just so I'm clear on this and got it right: you're saying it's just a perception and the focus is actually the same if I was using a CCD? The only reason I need to re-focus is because my eye is doing something?

[Paddy]

I thought that it would all be at infinity until I started solar observing and noticed that I need to change focus as I move from observing the solar limb to the centre of the disc and also between different solar prominences.