Ways to express "looking at from a short distance" - for native English speakers
What do you normally say when you talk about looking at something from a short distance?
Which of the following examples work?:

1. Look at the painting close up.
2. Look at the painting up close.
3. Look at the painting close by.
4. Look at the painting at close range.

Thanks for your help!

Question

Ways to express "looking at from a short distance" - for native English speakers
What do you normally say when you talk about looking at something from a short distance? 
Which of the following examples work?:

1. Look at the painting close up.
2. Look at the painting up close.
3. Look at the painting close by.
4. Look at the painting at close range.

Thanks for your help!

Answer

Definitely not 'close by'.  That has a different meaning from your intended one. "Look at the painting close by" is equivalent to "Look at the painting nearby" - in other words, a painting which happens to be near to whatever your reference point is.

"At close range" makes sense, but only if you were going to shoot it! "Close range" refers to a target. If you want an expression with 'at close..', you could say 'at close quarters'.

Of the remaining two, 'Look at the painting close up' sounds most natural to me.

Answer

I would normally use either #2. "Look at the paint up close".  I don't believe I would say "close up" in that situation, not saying that the phrase is incorrect or unused, but I wouldn't use it.  I would use "close up" if I was referring to zooming in on something.

Answer

I would say 'Look closely at the painting'. It's a slightly different meaning, but I think that in most cases that would be most natural thing to say. Of your examples, 2 or 1.