if I'm using the 1600mm lens because that lens doesn't have an auto focus option.. Its strictly manual focus.. Now, If I'm shooting a pic of a car, that is stationary and has lots of corners and other things that make it easier to focus on, no problem..
..but trying to shoot commercial jets - like I do - its extremely difficult because zoomed way in to a jet at 35K feet, its hard as hell to even FIND the jet, or star or whatever in the viewfinder.. and you can't zoom out, find it, and zoom in on it because the focus is so bad, you literally cannot see the object until you DO focus it - and you hafta be zoomed in where you wanna be to focus properly..
With a tripod, I can find the object, lock it down, and then concentrate on trying to manually focus, but without a focus aid (like a split image viewfinder) which, when out of focus, cuts the object in half, the two halves further apart the more out of focus you are.. as you get into focus, the two halves start coming together.. when perfectly in focus, the object no longer appears to be split into two..
Part of the problem focusing on the moon, for example, on a pitch black night is that its difficult to see anything on the moon to focus on.. a photography trick is to focus as well as possible, then lower the f/stop (which acts exactly like the iris in your eye), which will tweak the object to be in perfect focus - lower f/stops cause a greater range of distance to be in focus.. if you had the f/stop completely wide open, for example, ONLY your subject would be in focus.. anything in front, or behind your subject would be OUT of focus.. drop the f/stop and then stuff in the foreground and background will ALSO be in focus..
Problem is, you can't really drop the f/stop at night because you need the f/stop open as much as possible, because its dark.. you can compensate by slowing down the shutter speed, which allows you to close the f/stop, but its a game of what you can get away with.. another trick is raise the ISO as high as possible, then lower your f/stop, but then you get grain.. so, I'll quit babbling now..lol
Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..