Starship Asterisk*

APOD frequently states how many lightyears away an object is, which translates into looking that many years into the past.

How are objects at different distances imaged by a large, observatory sized telescope? Is the magnification changed? How? Does the focus have to be adjusted dramatically?

Aren’t all objects beyond a certain distance would come into focus at the setting of “infinity”?

worm wrote:Aren’t all objects beyond a certain distance would come into focus at the setting of “infinity”?

That's right: light rays from astronomically distant objects are parallel for all intents and purposes. A telescope focused to infinity will form clear images of anything out there, regardless of distance.

worm wrote:How are objects at different distances imaged by a large, observatory sized telescope? Is the magnification changed? How? Does the focus have to be adjusted dramatically?

Telescopes can't adjust their depth of field; they pick up light from all sources along the line of sight. Exposure time determines whether a telescope produces a nice image of a nearby bright object against a black background or a grossly overexposed spot amidst fainter, more distant background objects.