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Tom Parker
Приєднався 23 тра 2020
Mirror Quality Part II
This video starts with a summary recap of the criteria and analysis methods covered in Validating Your Mirror (Part I). It then uses them as a basis for discussion of other mirror quality terms that you may encounter as you read articles about mirror quality or mirror specification data sheets. If you would like to skip the recap. and go straight to the new material, you may fast-forward to minute 14:00.
The new material talks about four different mirror specification measures. It highlights the differences between surface error vs. wavefront error. Often times they are interchanged without your knowledge. Along the way, it takes a few minutes to talk about some considerations when evaluating secondary mirrors as part of your telescope's optical system. Additionally, it studies the Peak-to-Valley (P-V) measure and juxtaposes it with the Root Mean Square (RMS) measure. Additionally, with RMS, it talks about its intended application, it reveals its actual application, then highlights the difference between the two. It finishes with the Strehl Ratio measure. Once again, it talks about the difference between its intended application and its practical application.
The new material talks about four different mirror specification measures. It highlights the differences between surface error vs. wavefront error. Often times they are interchanged without your knowledge. Along the way, it takes a few minutes to talk about some considerations when evaluating secondary mirrors as part of your telescope's optical system. Additionally, it studies the Peak-to-Valley (P-V) measure and juxtaposes it with the Root Mean Square (RMS) measure. Additionally, with RMS, it talks about its intended application, it reveals its actual application, then highlights the difference between the two. It finishes with the Strehl Ratio measure. Once again, it talks about the difference between its intended application and its practical application.
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Відео
Telescope Optics Testing
Переглядів 10 тис.2 роки тому
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 di...
Mirror Quality Part I
Переглядів 1,6 тис.2 роки тому
This video covers the two most commonly established standards for a good mirror: the Rayleigh 1/4 wave criteria and the Danjon & Couder (D&C) criteria. While here, it takes a practical look at mirror wavelength ratings and shows you where you can get the most performance out of your mirror for your effort. Using data that can be collected via the test techniques discussed in Telescope Optics Te...
Autocollimation
Переглядів 2,3 тис.2 роки тому
This video dives farther into the autocollimation test. It is a superior test used by several amateur mirror making workshops including this one and has a long history of being used by professionals and amateurs alike. This video covers a brief history of the autocollimation test, discusses the minimum requirements of a flat, describes suggested features of a test bench, and reviews some of the...
Excellent and easy to understand. Thanks for making the video.
Very good! Thank's for sharing...
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.
Thank you. I’ve been wanting to set up this test and this answered most of my questions!
7:40 et seq. I'm a bit late to the party, I know, but I just wanted to point out that this depiction of 'peak-to-valley' error is wrong. You need to find the BEST-FIT parabola, typically making contact with both the edge and the centre of the mirror, and measure the maximum deviation from that. You can't show that in a diagram unless you depict the mirror surface as non-regular. Also, the Rayleigh criterion says that the reflected wavefront should be accurate to 1/4 wave, so the mirror must be accurate to 1/8th wave. I manufactured telescope mirrors professionally for 30 years.
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.
Thank you very much your videos😃👍 But i don't know focus(coc)constant ? Test data sheet column9 C=0.5641?? 1.How solve it constant value C=0.5641 2.what's mean column5. fomula hm/4f? and linght source is moving , hm/8f?? Thnak you very much! Clear skies😃👍
🌟⭐Thank you very much for this indeep Seminar about Optics and how to do assessments! 😊And how to interpret the results. 🤩 I will put this video-series to my reference collection 😉
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
This is really useful information thank you
Excellent
Thank you everyone for your compliments. My dad (who developed and narrated the content) is glad you're finding these helpful.
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!!
Excellent talk. Thank you so much.
Thank you very much. We're glad you find them helpful.
Большое спасибо, очень было интересно.
Very straight forward and easy to understand, thanks for posting!
Very interesting and well explained video. Thanks for taking the time and work to post this!
Fantastic explanation. Loved the easy and elaborated description. Will certainly make life easier for newbies like me. ❤️❤️
Glad you liked it