Ronchi 1.25" eyepiece to test the quality of your telescope on the star
The Ronchi eyepiece simply plugs into the 1.25" socket on your telescope and a medium brightness star (preferably the North Star) is observed. You will then see a striped pattern.
The closer you are to focus, the fewer fringes you will see and the more accurate the test will be. Three to five strips are optimal.
Using the stripe pattern, you can classify your optics without question and assess the quality of the optics. You can also identify an optical defect and classify it.
Combined with the star test, you can make a clear statement about your telescope with significantly greater practical relevance than an interferometric test can.
The advantages and characteristics of the Ronchi 1.25" eyepiece:
♦ Precise aluminum housing with clean 1.25" receptacle - no tilting possible
♦ Optically finely polished glass plate with vapor-deposited line grid – this ensures the highest level of accuracy when testing
♦ The glass plate with the lines is exactly in the plane where it hits the 1.25" receptacle. This means that the focus position can be determined to fractions of a millimeter.
♦ 10 lines per millimeter allows testing accuracy close to optical bench tests.
How do I use the Ronchi eyepiece?
It's easy to use, you use the eyepiece like any other 1.25" eyepiece. Take a medium brightness star and center it. With non-tracking (Dobsonian) telescopes, use the North Star because it barely moves and the right one is bright too.
Drive towards the sharp point (focus) until 3-5 lines are visible, then you will have the best accuracy. Then check the lines.
♦ Straight lines... everything is fine
♦ Curved lines... spherical aberration indication
♦ Parting lines...misalignment or astigmatism
♦ Lines with peak or valley... Indicates a zone error
There are instructions with sample images, you can download the PDF here.