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In fact, I also pictures that I tried to do Ronchi on a star virtually unseen…
But with the Foucault knife placed right next to the fire I can notice many details that the Ronchi usually do not see…Or better, you can not see very well if the entire surface tends to become “gray” simultaneously or if there are bad areas or is spherical…seeng permitting of course…Sincerely Massimo are not expert in star test and do not know be helpful…
However, it seems strange that you can not notice appreciable differences by increasing or decreasing the distance between primary and secondary…Although the ball was due to the mirror plane, Also like you said, you should still see an increase or subtraction of moving spherical mirrors…god!!!
You do not have the ability or know someone who has a flat mirror to make tests in Autocollimation?
Have you tried doing a test or Ronchi foucault directly to the focuser? maybe some clue might give it to you…Hello geminimac,
Welcome to the forum I too…
I agree fully with the suggestions you gave Giulio, the construction of a 400 / F3 is an extremely difficult, even for those with expertise in the field, and almost impossible for a novice…
Obviously if you dare to undertake this project, we will be here to help, but it would not then that the objective difficulties of implementation will bring to abandon everything in half work.
You just read the posts written by Massimo on the realization of its primary and secondary 300mm hyperbolic to understand the difficulties involved (and it considers that Massimo is certainly not the first mirror and has now already reached a certain level in the working hand of the optical).
I personally would recommend you start with something more manageable, kind 250, maximum 300 mm f6.P.S: precise that the arrow would be the primary 410mm f3, It would be well 8.54mm !!!
Hi Massimo, wow already at K = -3, you're going ships and with excellent results, among other things…
And, I also think that with the full diameter is difficult to manage such a deformed surface…I know that you also use the sub-diameters, I do not think at all that this will scare, view of the now great experience you have acquired…
Interesting these graphics…
But sorry Massimo, but then it would not be enough to stop with the polishing to a sphere with a radius of curvature of 8,5 mm longer than the final one of the hyperbola. Then during the hyperbolization you should be able to remove those 8,5 mm thus arriving at ROC and K desired.Hi Massimo, I could not answer…iperbolizzare clearly working towards the center and working outward or 70% also it allows to obtain the desired conic constant, but how well you say the three cases at the end will present slightly different focal lengths and it is here that my preparation is about an obstacle, in the sense that I have the tools and preparation to evaluate these small differences on the optical yield of the final tool.
The differences may be negligible or perhaps maybe not, not I have no idea. “Would not it be better to pre-calculate the ROC's caliber iperbolizzato ( with processing to 70% ) and take this value as a final radius of curvature of the convex ?”
It could be a good idea… And and, exact, sorry, I meant to say that technique you used to bring the two curvatures…
Even my touching the edges… Ah, Yes, OK, Now I understand why the images generated by the Ronchi Mel software do not add up.
Simply because he is using a tester with lattice and light source both mobile, while with others and even with my, generally the source is held fixed (You can also make the move by setting differently the parameters). That's why to get the same images I always had to double the distance from the center of curvature.
It is claimed, agree on everything…
With that technique you worked to get it back with the curvature and decrease the number of fringes?Hi Massimo
Ah here, I thought it odd that I could not quite see the rings…
Also I have come to see until well 20 Newton's fringes, that moved towards the center if practiced pressure on the center of the mirrors during the test. But now, with patience, I was able to bring everything just 3 rings, of which 2 concentrated at the center caused by the presence of a small hole (I must of course take off).In your case in which direction the fringes?responding to points I would say:
1)Well in short,, from images of Ronchi, the surface of the caliber I really seems a very good ball, starts at the edge retorted, but in that area we had already put into account the possible presence of an error…2)It is true that the two surfaces will be completely distorted by hyperbolization and is also true what you say that at this point it is important to fix once and for all the curvature radius of the central zone. That said, however,, I think that every one may want to move as want, in the sense that, also I have never found much sense in wanting to reach necessarily extremely tight ball and then having to destroy most parabolizzazione phase, but I always opted for a fair ball and then off with the other phases. But it is also true that this is the first time I've worked a convex mirror and probably I, in my project, first I try to achieve a good sphere with both glass, It is to take the test with hand, retouching etc., both because so I can be said to be able to build me at least one secondary for a DK before going over. So I think at this point of the work, the choice, it is more a choice dictated by personal preference rather than by purely technical reasons.
P.S: eh, Interestingly the result of the simulation…I will investigate…
By the way, which uses software to generate images of the Ronchi? try to compare them to the ones that come out of the “ronchi simulator” Mel Bartel (you find googol). You are equal?Hi everyone,
I made two Conticini and actually it is no coincidence that the fire “edited” proves “n” (1.52) times smaller than the radius of curvature. Here are the accounts in detail:In addition I modified Excel spreadsheet posted before, adding the ability to simulate the Ronchi also for other types of conical, you only need to change the value of the conic constant. I remember well that you can simulate the classic Ronchi test, so do not run from the side of the glass opposite, simply by setting equal to 1 the refractive index of the glass.
here it is:
https://www.grattavetro.it/wp-content/uploads/2016/04/Ronchi-inverso-parabola.xlsxP.S: I realized that the image that results from my spreadsheet is not exactly equal to that obtained using the “Ronchi Calculator” Mel Bartel, or that I did not understand how it works or is wrong (if you want I'll explain my reasons why I want to say this). While are identical to those which are obtained using other software such as: “Foucault Test Analysis” or “RonchiZ”
Hi Massimo, no, I had not noticed this fact…interesting…
Among other things, those pennies change as a function of the thickness of the glass, and it leads to low values and your observation goes to convergence…eh I have to think… P.S: In little program I did not put many warning, then mathematically calculations makes them the same, but it is obvious that from a physical point of view does not make sense to put the glass thickness values lower than what is the maximum deflection due to the curvature of the surface.
hello Giulio, I have the version 2010 Excel which of course support the .xlsx format. If I'm not mistaken this format should be supported only by versions from 2007 on.
Unfortunately I can not save it in the normal .xls format as this supports sheets with only 256 column, while only the area dedicated to the image formation Ronchi, in my spreadsheet, It occupies a square of 401×401 that. In addition to the format .xls the maximum number of characters to be included in each cell for formulas is limited and many of the formulas I used would not be calculated (just to make you realize the values at stake, this is only one of many formulas that fill a lot of cells for the direct calculation of “X rit – S” in sheet 3):
https://www.grattavetro.it/wp-content/uploads/2016/04/formula-Xrit-S.docxWith all these limitations so I can not just save the file in another format, because otherwise nothing would work. Even with libre office does not work, I'm sorry…
Absolutely yes, sure you can relate those two values, or any other two values of your choice.
If you look in the Excel sheet I uploaded before, you can change the distance of the light source (box B6 “dist. Light”), in this way you'll change the value in the cell just above (B5 “offset circa) which indicates at what distance from the curved surface must be to focus on the central rays…If you change the value of the distance light until it is equal to the value of’ offset circa, you get the value of the radius of curvature “edited” mirror.
Is’ interesting your idea of measuring the actual radius of curvature through this process, However, I do not know how it affects the non-perfect flatness of the surface “flat” on actual values and in addition the results of the calculations are strongly influenced by the value of the index of refraction of the glass, to be known precisely if you want calculations and reality are compatible.
This is to say that would not be all easy, But the method I find it interesting and I think it is worth deepen. If you can make accurate measurements on your mirror and then we can discuss best by comparing simulations and reality…
