Infinity Focus

This might be dumb, and maybe quite obvious... but I gotta know.
I've spent a great deal of time in photography, both professional as well as amateur and now am interested in amateur astronomy. Every camera lens I've ever used or have seen, reardless of focal length, diameter, etc., all have 'infinity focus'. Kind of set and forget when it comes to great distance.
However, telescopes need to focus regardless of the distance to the object. Why?

I have a few theories, but to save the guessing... I thought I'd ask here

Thanks,
Trevor Hoffmann

Because telescopes do not have infinity focus stops and depth of field takes on a whole new meaning for astro objects. The telescope can move from intra-focal through extra-focal positions with respect to a varying focal plane.

Camera lenses have stops that prevent such focus flexibility for infinity, but as you know macro extensions can be used for close-ups. This applies to telescopes as well.

I think Mitch's "Second" answer relates to the heart of your question.

Basically, telescopes often require refocusing for different eyepieces.

A given lens/camera system woud be analogous to a given telescope/eyepiece system. Switching eyepieces is similar to changing the spacing between two or more lens groups in a camera lens. If you could set the camera lens to infinity, *then* move one of the elements or groups within that lens (while the ring is still set at infinity), then you'll likely end up focused at something *other than* infinity.

Hope that helps.
-Dan