Telescope Optics Testing
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- Опубліковано 19 гру 2021
- This video covers the several different methods that can be used measure the shape of your telescope mirrors. It describes the underlying principles behind the null test along with the use of the Ronchi screen. It explains the conditions under which various mirror shapes will produce a null return. It defines spherical aberration and then studies how you can use it and a knife edge to reveal different characteristics about your mirror.
It explores four tests that use a knife edge, or a variation of it, to measure the spherical aberration including: the Focault knife edge test, the Ronchi test, the wire test, and the caustic test.
On the other hand, null tests provide the advantage of returning a single, immediate result. The video covers five null tests that are at the mirror makers disposal. It explains the Mobsby screen, the artificial star test, the Dall and Ross tests, the autocollimation test and finally the star test. By the end of this video, you will have a good understanding of the tests as they are being applied in the workshop.
I just chanced on this video, which is excellent. I was a mirror-maker for 30 years, and eventually alighted on what I refer to as the 'inverse wire test'. Take two photographs - on film - of a thin wire against the sky background. Use one of the resultant negatives as the light-source slit, and the other as the knife-edge. All the dispersed light is screened out, and you will see a diffraction line adjacent to the knife-edge image. You can use that diffraction line to get a more accurate measure of each zone.
Excellent and easy to understand. Thanks for making the video.
Very good! Thank's for sharing...
Thank you everyone for your compliments. My dad (who developed and narrated the content) is glad you're finding these helpful.
@Ken Fullman The best I have is a few photos from one of the workshops. In the "Day 8" photo grou is the autocollimation test bench. There, he used a video camera so the test result image could be put up on the TV screen. However, you can just as easily put your eye there. There's no cause for a trip to the hospital.
mirrorworkshop.mtbparker.com/workshop12.html
This is magic, there is no better explanation that exists in the whole world. I'm making a 7" f6.7 and this helped me to understand howto quantify my mirrors performance
Fantastic explanation. Loved the easy and elaborated description. Will certainly make life easier for newbies like me. ❤️❤️
Glad you liked it
It's mind blowing that 19th century method, extremely simple cause practically anyone can arrange the Foucault knife in every kitchen, has a micron accuracy;) And it's been used nowadays.
great job. your gratitude with astronomy had been paid with this job. Far from istronism of others collegues whose makes videos for its names and null for usefull information. thanks Tom ! now we can go for the same celestial way!!
Very straight forward and easy to understand, thanks for posting!
Excellent
Большое спасибо, очень было интересно.