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To carry out serious autocollimation, you need a mirror with a diameter equal to or greater than that of the mirror you are doing, so for 1 meter it takes a floor of one 1 metro, with hole in the center and with surface precision 1/10 wavelength. Unfortunately I cannot have such a thing and therefore I have to do differently.
For the primary
1) hyperbola generation with measurements made with Foucault using the Texerau formulin
2) I also use the Ronchi reticle
a lot of patience and a good dose of luck !!!
For the secondary
1) generation of the shape with verification of the fringes on a spherical mirror (as for the Cassegrain)
2) once the primary is well done, continue to work on the secondary, checking with mirrors mounted on a distant point source (artificial star)
and here too much luck !
Or a nice Zygo interferometer and let's solve the story
This is basically what I think I am doing …… then there will certainly be variations during construction, as always
However I also have a home made Bath Interferometer which helps in more serious cases …………..
Obviously I have to do even the secondary, which in practice, with our modest equipment, It is done ” on the primary” . Fortunately, it is not the first time that I do an R / C, although not of this diameter. The processing is not very dissimilar to a Cassegrain. You know the formulina spherical aberration which is on Texerau ? The whole trick is to use that well ………
In fact it is definitely exciting, for me that I have a lot of glass grated, get your hands on a blank from 1 metro ! In any case there are difficulties, all right ! The focal length of the primary is not so much thrust as the thickness is just 57 millimeters, then a super thin. Is’ almost a meniscus. To be able to work properly I had to make a machining cell that presents similar points of support to those who will then be used in the real cell. Glass is a Pyrex 7740 Corning Glass, now no longer in production. The conic constant of the secondary is marked but not impossible. The biggest hurdle will be at the time of obtaining the correct form, which as is known is a hyperbola.
The insulators have them taken by a local material recovery, shredded and then placed in the oven. My friend often melts the glass for artistic purposes, although not in the thickness serving us, so it's still a good experience about. After a few tests we were able to get two blank: one from 21 and one from 31 centimeters thick 40 millimeters approximately. One of the problems is that the bubbles, very common with Pyrex. However, we noticed that they tend to form near a side of the blank. The biggest problem is now the cooling curve that must be carefully studied and proven. There are still several tests to do. If my friend helps me yet, possibly retrying.
The blank from a meter is during polishing. But now I had to temporarily suspend work in order to prepare a more suitable environment in which to do it. I currently too little space, which it is also critical for optical tests. To move it you need a davit
I'm trying to do. It weighs more than 100 Kg, then move it by hand alone is unthinkable, also for the risk of any falls. To put it on the machine I had to get help from other 3 people. When do I take a few photoshello Maurizio,
I in 2010 I did some tests with the help of a friend who has the oven very similar to the article you mentioned. We have done something with pyrex made from old insulators for power stations. I must say that the result was satisfactory but then we did nothing because, sincerely, the work behind this thing is not trivial and certainly it takes considerable experience.
