Experience fully building a 600F3.8

[Giulio TiberinI]

The very detailed Manufacture of the mirror is described in a very interesting here
http://www.astrosurf.com/magnitude78/telescopes/T600/fabrication.html

As always in magnitude78 things are very instructive and interesting to meditate upon.

NOTE adding the 4/8/2019: They then occurred work resumed to complete this difficult mirror, as described later

[Massimo Marconi]

Ah yes Giulio, everything is beautiful… the cars, the glass, in tests… But here as in many other parts, I do not see published an effortless Ronchi would give much guidance on the result.

As I said to the, it is my belief ( but maybe it's me that I'm wrong ) that does not parabolizzare is successful with a full-diameter F3.8.
I wonder why Gordon Waite, ( instead the test results public, and they are a wonder ) do not use these procedures for the mirrors but it is often seen retouch by hand with very small tools…

[Giulio TiberinI]

In fact meditation is a must for better or for worse

[Massimo Marconi]

I correct myself, something published on the polishing test, and in fact there are problems…

[Giulio TiberinI]

This addition is due to the fact that, I noticed, that the mirror diameter 600F3,8, not finished in the document referred to in this link in the first post of this thread, He has had a following and a term with a lot of tests, it seems to me interesting to read:

After a long downtime for metabolization of several objective difficulties encountered, despite the technical work of amateur astronomers respectable, It took place the resumption of parabolizzazione until the end of the mirror, with related tests

http://www.astrosurf.com/magnitude78/telescopes/T600_site_V2/miroir_fin.html

Alas, however, it is Foucault tests ... which unfortunately for his fundamental physical principle, it is not appropriate to short focal lengths of large diameter mirrors:

A test "Caustic" probably would be less subjective (as "caustic" is A unique bright vertical bar that presents the clear absence of diffraction lines, it is easier to identify than the "flat" shadows to match and evaluate on TWO windows of the mask Couder, with Foucault test).

But mostly the "caustic test" is born to replace Foucault in achieving short and large diameter focal ratio mirrors, because the center of curvature of the areas of the short focal lengths and large diameter, It falls only optical axis for the first zone (center mirror); while for all other areas of the center of curvature it falls on the curve "caustic", which it has the shape of a trumpet pavilion, and that always goes farther and farther away from the optical axis, as much as the diameter of the mirror is greater than 300mm, then gradually moving away more and more from incorrect data supplied by Foucault, as they measure the drawdowns of the zones gradually towards the edge mirror, where tolerances are always the most restricted.

The optical axis is instead the place taken as a reference by the Foucault test, because of focal ratios equal to or greater than F5, the discrepancy between caustic curve and the optical axis is very small and negligible.

Some info on the caustic test is here: https://www.grattavetro.it/test-della-caustica/

I suspect that one large mirror and a lot “Fast”,realized according to the Foucault, always give the star test the suspicion that there is something wrong in areas beyond 70%, and that there has to content.

Apart from anything else, It is very interesting for any "grattavetro", download the Excel file titled "carnet des retouches", with at the bottom of the final link parabolizzazione.

That Excel spreadsheet describes each of the numerous tweaks implemented, specifying action, type of tool diameter sub, and processing times, in addition to presenting the results of the subsequent tests Foucault.

As always in magnitude78 things are very instructive and interesting to meditate upon.

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