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Amateur Telescope Making

How to make a Ronchi Screen

Contributed by Clint Bach

You can easily make your own Ronchi screens .

Procedure:

  1. Take two strips of dimensionally stable material about 3/4" wide and 3/4" or more long. Drill matching holes in the two strips of material about 3/8" in diameter and tape the two strips together. I used 3/4" by 1 1/2" 1/8" extruded aluminium with 3/8" holes for my Ronchi screens. Note: The material and the dimensions are not critical.
  2. CAREFULLY wrap TWO strands of monofilament fishing line around both pieces of taped together Ronchi screen material. Make sure the monofilament is not crossed and is evenly wrapped around the future screens with no gaps between the strands. You only have to wrap enough line around the future screens to cover the hole.
  3. CAREFULLY unwrap one of the strands of monofilament.
  4. Glue the remaining strand of monofilament securely in place.
  5. Cut the strands of monofilament between the two screens and you have two matching Ronchi screens.

I first tried making screens this way with fine wire and was not happy with the results. The wire will kink while being wrapped and monofilament won't. The monofilament is tough and very forgiving to bad handling. The surface of the monofilament is much smoother than wire. Clear monofilament is OK. Some monofilament is labled with its diameter. (1.5 pound is about .004 inch which makes about a 125 line per inch screen) Different thicknesses of line make different screens!

Since there is no substrate to look through (glass or plastic) there is no distortion caused by the substrate. The lines are perfectly straight. Well if not perfectly straight I'll bet you can't measure the imperfection!

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