My present

[Marco Guidi]

Hi guys,
maybe someone will know me ,my name is Marco Guidi ,I am a HIres astrophotographer http://www.marcoguidihires.com obtaining international APOD NASA awards and international publications ; I often lecture at UAI congresses on high resolution photography and related issues. Recently also a telescope manufacturer http://www.doctelescope.com ,this happened after over 10 years of self-construction of my tools .
I call myself a strehl maniac 0,9
I finally made up my mind to start the self-construction of the optics and then propose a completely made in Italy product .
Tomorrow I will start working on a 305mm f5 blank in pyrex and a full diameter tool in common glass.
I already have the dedicated table because I had it made about 15 years ago having produced a 250 f5 in pyrex that at the time I had made under the guidance of a friend who already had and has produced various diameters from 250/300/40/500 and now it is realizing (already in the polishing phase) an 80cm f4 ,I consider this person prepared and capable because well-known Italian producers have seen his creations defining them as excellent .
The mirror that I will start tomorrow in reality is already abrasive 600 finished then my work will start from the 19th century .
I have dedicated this last period to review all the processing phases and the grattavetro has played the lion's share!
My goal is to produce diameters between 30 and 50cm with focal lengths from f4 to f5 knowing all the difficulties of the case ,I gave myself a time of 2 years even if the way I have of reasoning and that I have always avuo is ”never finished learning”
The thought I have right now is the control system , the person I know uses the focault with its coudè mask, however, I felt that the null test is more immediate and more precise .
I have already requested to equip myself with a flat mirror to use the control system in autocollimation .
Tell me what you think
He believed I will learn a lot here
Thank you
Marco

[Massimo Marconi]

Hello Marco, welcome ! Is’ a pleasure to have you here, we hope to be able to help you with this new adventure of yours.
I see that you have clear ideas about the goals you want to achieve and this is definitely a good start !
Therefore a “good luck” and I will follow with interest what you want to share on our pages.

Per i test, I think it is quite a broad discourse, anyone and anyone can do well, it depends on many factors, including the ability and aptitude of the operator with a certain test, in a way it is a bit’ how to ask which software is better for image processing.

Perhaps the best thing is the use of multiple methods for the same surface to be checked, it being understood that, from what I've seen so far, the only one that “never lies” is the star test.
For those like you who have the opportunity to have an instrument with a reliable structure available even before having finished the optics, the star test is certainly to be taken into consideration as a verification of the results obtained with other methods.

[Marco Guidi]

Hi Massimo and thanks for the welcome , I add in addition to what I have already written that the method that I have seen to be infallible several times is the roddier test also performed in the laboratory with a flat mirror ,this is why I am directed towards this methodology,the Roddier test ,if performed according to the canons , provides extremely precise parameters indicating exactly the value of any defect, this I verified with spherical errors that emerged on the sky and confirmed the laboratory.
What is certain is that at the moment this is difficult for me not having a flat mirror ,but it will come….

Marco

[Giulio TiberinI]

Marco Guidi wrote:

Hi guys,—– I have dedicated this last period to review all the processing phases and the grattavetro has played the lion's share!
My goal is to produce diameters between 30 and 50cm with focal lengths from f4 to f5 knowing all the difficulties of the case ,I gave myself a time of 2 years even if the way I think and that I have always had is "never finished learning"
The thought I have right now is the control system , the person I know uses the focault with its coudè mask, however, I felt that the null test is more immediate and more precise .
I have already requested to equip myself with a flat mirror to use the control system in autocollimation .
Tell me what you think
He believed I will learn a lot here
Thank you
Marco

Hi Marco and welcome also from me.
As for my knowledge as a non-professional scratcher, albeit supported by passion and study of foreign stuff for my own business (given the absence of Italian books also due to the scarcity of interested parties that the subject encounters in Italy) I am sure that the autocollimation control method is the one that is the most popular at a professional level, and well suited to the range of diameters and focal lengths you have in mind.

Method that I know so alone “academic” , having never applied it due to the prohibitive expense to equip themselves with a lambda / 16 flat mirror with a diameter at least equal to the maximum diameter that you want to produce. Expenditure that includes a test case, and it is justifiable if its amortization is foreseen to be spread on a certain number of mirrors to be put up for sale.

(the flatness a 1/16 of lambda is necessary for those who plan to work mirrors with focal ratios not lower than F4, since the focal ratio is part of the formula that determines the tolerance of the autocollimated measurement).

Americans like Parker say the sensitivity of the method is excellent while using it “poor” Ronchi lattices from 5 lines millimeter, than we Italians used to 10 lines, they are at least strange.

The Foucault test in my opinion (that I am a staunch supporter of it) despite its intrinsic objectivity (given by having to judge by eye whether two shadows are of equal intensity) it is invaluable help, and it is the only test “quantity”, that is, it allows to know “how many nanometers” glass I have to remove, or I have exaggerated to remove, and it would be advisable if you want to achieve a certain quality.
I also understand that craftsmen dodge it because now they are done “the Eye” to corrections with Ronchi…But it is useless for them to go around telling stories, because no one is able to judge nanometers by eye, who are the ones that Foucault tells you (albeit subjectively), and they are also the ones who make the lambdas / two digits.

Which Ronchi or autocollimation do not say, providing only an image of the location of any defect, which with its curves suggests the quality of the optics, but that does not help with numbers to understand how deep it is and how consequently the scratching actions suitable to correct it must be long over time.

While the Roddier test cannot be used when making the mirror, because it is applicable only to the finished optics and does not allow you to see what happens on the parabolic profile of the surface being processed.

All new commitments represent new ones “go up” which are a little more tiring at first, but the trick to succeed is not to make simplifying inventions right away, but trust the techniques in use, only learned well which are certainly carried out excellent customizations.

…Lots of chatter, but I hope you will find yourself well here.
Ciao
Giulio

[Marco Guidi]

Giulio Tiberini wrote:

While the Roddier test cannot be used when making the mirror, because it is applicable only to the finished optics and does not allow you to see what happens on the parabolic profile of the surface being processed.

Hi Guilio and thanks to you too for the welcome,you are definitely right , I forced myself not to make strange inventions and to follow and start with the focault even if I have seen various mirrors in autocollimation and it is true,they say where it is at fault without quantifying it.
I must tell you that the roddier is perfectly usable with the flat mirror in autocollimation with the use of the laser that simulates the star , I also verified the perfect correspondence with the response of the roddier with images taken with a star in the sky ,I talked about it at the lecture I gave at the high resolution meeteng UAI,i also have screenshots if you care.
The optics featured a 30nm spherical lens concentrated at 5.5cm from the outer edge ,matching measure both with roddier carried out on the sky and with roddier in the workshop.
What I aspire to would be to equip the mirrors I produce with this documentation, it will not be steep tomorrow ,but that is the intention.
Returning to the 305mm that I am making ,during the week I will prepare the pitch since I finished with the 800 passing at 10 hours of polishing
See you soon
Marco

[Giulio TiberinI]

On the Roddier my knowledge is only theoretical, and I believe that its possible use parallel to other tests underway “scratching” can be a great thing. In fact, the cross-use of multiple complementary tests is a source of security not otherwise obtainable.

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