focusing why bother ?

[Stevie816]

Just been thinking,

All the things i'm looking at are millions of miles. or millions of light years away.

So why do I have to keep focusing ?

On my camera anything more than about 100 yards away is at infinity, So what's going on with the scope ?.

Steve

[knobby]

Interesting question ... something to do with depth of field?

I'd love to know the answer to this one too!

[Capricorn]

You shouldn't have to.

Everything is at infinity so the image should be at the focal plane always.

Something has to be altering, if you are changing eyepieces then it is it the object plane of the eyepiece that is changing.

The other bit of optical equipment is your eye. As you move away from the eyepiece to adjust the scope, as in move to another target, you have to alter the focus of the eye to bring near objects into focus. Then your eye does not return back to exactly the same state as when initially viewing. So you adjust to scope to account for your eye change.

The other factor is that you may adjust your eye to get a sharp image initially, and after moving the scope you do not adjust the eye to achieve a sharp image but adjust the scope.

You need a bionic eye.:D