1.25" Ronchi eyepiece to star test your telescope

Just put it into the 1.25" receptacle of your telescope and point at a star of medium magnitude. Best is the pole star as no tracking is need in this case. Then, you will se a stripe pattern.

The closer you are to focus, the less stripes are visible and the more sensitive is the test. Three to five stripes are optimal.

By interpreting the stripe pattern, you can classify optical abberations and the overall quality.

In combination with the star test, you can make much more useful statements about an optical system an an interferometric test can do.

Advantages and characteristics of the Ronchi eyepice:

♦ Precise aluminium body with 1.25" diameter - no tilting
♦ Fine optically polished glass substrate with precise grating for high test precision
♦ The grating side of the glass is exactly on the same level as the hard stop of the 1.25" barrel. So the focal plane of the telescope can be measured exactly.
♦ 10 lines per millimetre allow a test precision close to a optical bench

How do I use the Ronchi eyepiece?

Operating is easy. Just put it into the focuser as any other 1.25" eyepiece. Aim at a star of medium magnitude and center it. A comfortable star especially for Dobsonians and other telescopes without tracking motor is the pole star as it does not move and has the correct brightness.

Turn the focus wheel until 3-5 stripes are visible. Then, examine the stripe pattern.

♦ Lines straight and parallel: Everything is OK
♦ Curved lines: Hint to spherical abberation
♦ V-shaped pattern: Decollimation or Astigmatism
♦ Lines with "hills" or "valleys": Hint for a zone error