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Hi everyone, it is a bit’ I do not make me feel…
They are nearing completion of a telescope 30 with low profile (optics had already been finished last in the short winter will also post the images). I write this new post to get some information about the glass alternative materials, as it blends for the head the possibility to realize a view to larger (around 50-60 cm), but I found a lot of difficulties in finding appropriately thick discs, so I was wondering if it could be good that even the marble or the tile, It has several times used as a tool to the grain 1200, and it is incredibly similar to glass.
Some time ago I stumbled upon a video on YouTube where a German amateur astronomer has created a steel optical glass comparable to such a view performance, and so I was wondering if maybe you can do something that I do not say steel looks a little’ however extreme perhaps with other materials.
What do you think?hello Luigi.
I apologize, but I was on vacation and now I only see your writing.To answer your question that no metal possesses the structural stability characteristics over time and surface uniformity, and also of low thermal expansion,, acceptable for the realization and the maintenance of the form of a precision optical surface as understood and request to our days to these tools.
the degree of polishing and precision of the parabolic curve that must submit the optical surface of a reflective parabolic mirror "diffraction-limited system" even if only to a minimum entry level of quality to Lambda / 4, It must be such as to present on more roughness than one-eighth of the wavelength of the yellow-green light, to which the human eye is more sensitive, the extent to which 550 nanometers high..
Therefore, the maximum tolerable asperities left by a surface defect must not be greater than (550/8)= 68.75 millionths of a millimeter.
At the dawn of astronomy, reflector telescopes, a bronze was used to "grit special" order for optical, because only starting from 1856, Leon Foucault and Carlo Augusto Von Steinheil perfected the glass manual machining system for abrasion, which it is still implemented to achieve a mirror.
In fact, the choice of glass was determined by the fact that, contrary to all metals it is resistant to oxidation at room temperature, and is an amorphous solid, ie free from any crystalline structure. (Although for this reason it is scientifically considered to be a liquid at room temperature has a degree of infinite viscosity).The fact that on any base material different from glass, for the realization of an optical mirror, is present a crystalline structure (and then reticular), It presupposes the existence of greater hardness lines that lead to a different abrasion efficiency, which is opposed to the necessary workability of the surface homogeneity, and it carries with it the impossibility of achieving the quality that is achieved today with glass.
In conclusion, the metals are tough, heavy (removing the aluminum which weighs as glass) and much more difficult to work with glass.
hello Giulio, no problem, God forbid…Mica does not have the availability…
I read something on the marble. Granite seems that is not good, while the marble, especially that of Carrara think you.
You know something about this?hello Luigi.
No, marble like blank mirrors do not know anything. But what little teaching geology I know and sense of proportion optical processing, it seems strange, if not impossible that a natural mineral may have a lower particle size and uniformity to the famous 68 nanometers high..
Why watching closely, if already only with a magnifying glass they can be appreciated zones of the granular or at least similar to crystals different from other neighboring, It will become impossible to polish in a uniform manner with the minimum accuracy very demanding.the James Webb Space Telescope mirrors are beryllium, which in any case it is a metal…
from wikipedia:
The primary mirror is constituted by 18 hexagonal elements beryllium flanked honeycomb. Each individual mirror, the size of 1,4 meters, It is covered with a thick gold foil 1000 Angstrom (100 nanometers high.), which better reflects the infrared light.[21] The gold foil is in turn covered by a thin layer of amorphous SiO2 (glass) to protect it from scratches when handling or small particles. In the launch phase the primary mirror is compacted in 3 sections and stowed in the rocket; subsequently it deployed with micromotors. The optical technology of JWST consists of three mirrors anastigmat. In this configuration, the primary mirror is concave, the secondary is convex and it works slightly off axis; the tertiary mirror removes the resulting astigmatism and also flattens the focal plane.[21] This also allows a wide field of view to produce images without optical aberrations. It is also used a fast power steering system to enable image stabilization. The optical unit is provided by Ball Aerospace & Technologies Corp. sub contractor Northrop Grumman Aerospace Systems.Other materials including silicon carbide ( which it seems to be better than the glass also ) They are used to produce optical , Zygo has even list them:
https://www.zygo.com/?/opt/components/mirrors/siliconcarbidemirrors.htm
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