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How to Clean an Old Refractor Lens

Over time, small amounts of dust and other debris can accumulate on a refracting telescope's objective lens. In most cases, this will not degrade the optical performance of the telescope, and the lens is best left alone. If these accumulations become serious, then it may be necessary to clean the outer surface of the lens. Always use extreme care when cleaning telescope lenses and mirrors, as they are easily scratched and the coatings can be damaged. As a general rule, you should not clean a refractor's objective lens unless absolutely necessary.

Things You'll Need

Blower bulb/camel hair brush combination, or the individual items
50 percent solution of glass cleaner and distilled water
Sterile surgical cotton

Instructions

- 1
  Blow any loose dirt off the lens, using the blower bulb, starting at the center of the lens and working towards the edge. Gently brush away any stubborn particles, using the camel hair brush and the same method. If you see materials other than dust on the lens, such as eyelashes or other debris, do not not brush them -- they could scratch the lens.
- 2
  Make several balls from the sterile cotton. Soak a few balls in the cleaning solution, then squeeze them sufficiently to stop any dripping.
- 3
  Wipe the lens thoroughly with a wet cotton ball, applying no pressure other than the weight of the cotton. Immediately wipe the lens with a dry cotton ball, using little or no pressure.
- 4
  Repeat Step 3, using fresh cotton balls and very light pressure. Blow off any surface lint, using the bulb.
- 5
  Examine the lens and cell to be sure they are free of cleaning solution. If liquid is found anywhere, leave the telescope with the objective lens uncovered in a warm place until it is dry.

Astronomy