Distance between objective lens and eyepiece I am trying to make home telescope, I have a convex lens of focal length 1000mm and eyepiece (plano-convex) with 25mm focal length. What is the ideal distance between objective and eyepiece to see objects more than one kilometre away.
tl;dr: 1025 +1/-3 mm
If you were to focus at infinity, then the primary focus is 1000 mm from the primary lens and you would put the eyepiece lens one of its focal lengths away from that point to make a new parallel beam. That's 1025 mm. If your eyes can not focus at infinity without glasses, then wear them so that you can see the parallel beam and image it on your retina.
If you don't have your glasses or would like to try without, then your eye needs a diverging beam which means the eyepiece should be a little less than its 25 mm focal length from the primary focus, i.e. a tiny bit closer to the objective, perhaps 1 or 2 mm.
Now you mentioned that objects are over 1 kilometer away from your telescope. If they were exactly 1 km (1,000,000 mm) then the primary focus would be farther from the objective by a little bit.
The thin lens equation 1, 2 is
$$\frac{1}{d_{img}} = \frac{1}{f} - \frac{1}{f_{obj}}$$
so your image distance would then be 1001 mm, and so you'd have to move your eyepiece away from the objective by 1 mm to correct for that.