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How to Focus a Refractor Telescope

A refracting telescope uses an objective lens to bend light to an eyepiece so it can gather more light and magnify an object that is far away. The eyepiece must be at the exact distance so the light coming into, and being bent by, the objective lens converges on one point on the lens. This will give you a clear and focused image. To focus a refracting telescope, there is a knob right by the lens that you can use to move the lens in or out to focus the image.

Instructions

- 1
  Place the telescope on the tripod and level it. The tripod that came with the telescope should have a level on it or you can use a level. You need to have the telescope leveled before focusing it, as it will need to be focused again if you move the telescope.
- 2
  Point the telescope at a bright star. Lock the tripod so that the telescope is securely in place and can not move around.
- 3
  Grasp the knob that is just by the lens; while holding the knob, place your eye against the lens.
- 4
  Turn the knob and see if the light in the lens becomes more focused. Keep turning the knob in the direction that helps to focus the image. Once the image comes into focus, turn the knob a little more until the image goes out of focus a little. Turn the knob back until the image is highly focused.
- 5
  Focus the lens as you move the telescope or as it goes out of focus. Fluctuations in the temperature can change the focus on the telescope, so focus it as much as needed.

Astronomy