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.
@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
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!!
![ILLSLICK X YOUNGOHM - We're The same [Official Video]](http://i.ytimg.com/vi/yUJNkobYR0E/mqdefault.jpg)
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 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
Great explanations
Fantastic explanation. Loved the easy and elaborated description. Will certainly make life easier for newbies like me. ❤️❤️
Glad you liked it
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
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.
Very straight forward and easy to understand, thanks for posting!
Excellent and easy to understand. Thanks for making the video.
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 good! Thank's for sharing...
Большое спасибо, очень было интересно.
Excellent