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hello Luigi, sometimes happens… solution: Immersion in warm water, They should disconnect almost immediately !
Mah… I also would try to ask the builder, as the optimization of the optical RC is linked to the construction parameters that only the designer knows exactly.
For example, a small displacement also one-two mm from the correct distance between the primary and secondary can cause, as well as a variation of the overall focal length of some cm, a spherical aberration ( otherwise nonexistent ) which would lead to think that the optics are faulty.
The basic parameters to be known x optimize the whole system are:
-distance between the mirrors (You can, however, derive primary knowing F, F complessivo e Back-focus )
-back-focus
-Cpl
-The focal length of the primary It can be measured directly as you would with a parabolic mirror, hyperbole because the deviation from the primary reference parable is really small . Generally, the focus of the primary is outside the optical tube and can also be measured with ease without removing the mirror from the telescope. the limits, if you do not want to make a measurement off-axis, it would be convenient to remove all the support of the secondary before carrying out the test.
– The focal length of the secondary however, it can not be measured directly, and also the value of the hyperbolic conic constant is of a higher order of magnitude to the primary and the difference on the focal plane ( negative ) You are felt all right ! However for the purposes of optimization of the system and the calculation of the hood, the secondary values may also remain unknown ( assuming that the optical is correct ), They are sufficient values of the back-focus and the distance between the mirrors, at that point there is only a hyperbole of the secondary verification that this specific configuration, and then the respective parameters are deduced analytically, although we hardly needed to use them, just in case we were to notice that the resulting system is not correct.Welcome again Antonino, it is a real pleasure to make your acquaintance, I saw (unfortunately only on the internet ) the Lilio Astronomical Park, a beautiful structure and instrumentation, congratulations !
Hello and welcome Antonino !
to calculate the diameter and length of the lens hood is necessary to know other data relating to the optical scheme:
-focal length of the primary
-Backfocus
-CPL (field full light )these data, together in diameter and overall focal, They can be used with any of optical design software, for example ATMOS available in the demo version (free) in our pages download
After installing the software you can access the preset configurations of the Cassegrain and enter the relevant data, at that point Atmos may calculate all of the missing data for a RC configuration:
-diameter and focal secondary
-distance between the mirrors
-conical constant of the mirrors
-primary lens hood
-Secondary lens hoodYou can then try installing the software, or, if you prefer, We send us the missing data and calculate the lens hood
I made a mistake in judgment and I apologize for it… In the last image of Ronchi, to be in the “vicinity” of the parable of a 300/1700, the reticle used should have 5 lines / mm and not 4 lines / mm as I erroneously said.
In the following image you can see the display difference of the parabola of a 300/1700 with a lattice from 4 l/m ( at left hand ) and one with 5 l/m ( to right )
Luigi, what you write is in my opinion a further confirmation on the problem of adaptation.
Having off-centered the tool, you went to work the areas that were previously partially reached, you have deepened the area a 3/4 of the diameter and in fact the connection with the median zone is now more continuous and uniform.I am not saying that the precautions you take are not right, I say that ( indeed Ronchi says so ) they were not sufficient to guarantee the maintenance of the pitch shape in all sessions, adaptation is necessary in each session, its verification comes from the analysis of the processing results, the only way to be sure of the good fit with the full diameter tool is when the technique ( performed correctly ) produces the expected result.
The good news is that now you don't have a sphere but a decent parable
, still missing to fix a bit’ of roughness in the center which so far has only been partially affected by the machining.
I would do some measurements with Focault, I don't think you are very far from the final parabola if the reticle you used is around the 4 lines / mm you are very close to it e, if the polishing is complete, the sphere at this point is not even needed…Luigi, I believe that the problem is precisely adaptation: the half-diameter depression deepened further, while the center and the border have remained unchanged. Ronchi tells us that there is an area that is working more than the others and this with the past 1/3 D shouldn't happen.
Extending the strokes could help as the action of the tool would be extended, which now seems confined around the area a 1/2 D.
But the question in my opinion is another: if the 1 / 3D runs do not lead to the desired result, because the application of another technique should do it ?
I think it is better to find the cause that is determining this anomaly, the technique cannot be because as we know racing 1/3 D lead to the sphere, but only if all the rest of the setup is ok.The outside temperature of 11 degrees makes me think that, apart from the contact surface, the pitch is too hard to match the mirror, it is not able to deform to adapt to the evolution of the shape of the surface, moreover, in the transition from a warmer to a colder environment, there is certainly a variation in shape, perhaps imperceptible to the eye but very perceptible by cerium oxide.
I would continue with the central 1 / 3D runs up to the sphere, above or below in my opinion makes little difference. Rather, we should understand why the periphery has a tendentially different trend from the center which is instead spherical.
Almost always the cause is a suboptimal adaptation of the pitch patina, in which the center has a better contact than the periphery.
I would therefore also try to insert micro-grooves in the pitch squares, which certainly help both in the mirror-patina adaptation operations and in the effectiveness of the races.To be checked even if with the lowering of temperatures these days the patina is not too hard.
Great job Luigi, the image of the ronchi is ok !
Don't worry, there is no astigmatism, the center is spherical, then there is a small depression at half diameter and a decreasing peripheral area, but nothing that goes out of the ordinary, normal aspects and corrections to be made during polishing to get to the sphere.
overall the figure is good, perhaps there is a slight roughness in the peripheral part that should disappear with the end of the polishing, I continue to read you and I am very pleased to see that slowly the "family" is expanding, still not complete.
There is also a small difference in brightness between the left and right sectors which makes the opposite bands appear to be of different thickness. but this depends on the imperfect symmetry of the slit in front of the light source.
If the light source is a led, then part of the slit intercepts the brightest point of the LED, in practice the slit is not perfectly in the center of the led, but they are details, the substance does not change, it's a good job !
Stefano actually makes some beautiful pictures and, waiting for you to reveal yours “secrets”, I can tell you that, looking more at your images I think there is an exposure problem, as the background which is much less bright than the source, instead it appears correct as an exposure. This happens because the device used averages the brightness of the scene and calculates the relative exposure ma, in this way, consequently it overexposes a small area of greater brightness which is precisely what interests us. Therefore a first optimization consists in changing ( where possible ) the automatic exposure setting with the manual one by entering lower values, until the rest of the framed scene is fairly underexposed, quasi “darkened”.
hello Luigi, try if you can, to take pictures decreasing contrast and exposure, but in any case it occurs before the slit in front of the light source is thin enough , otherwise it may happen that the Ronchi lines do not show their true aspect , but they may be altered by the excessive width of the slit.
If what you see by eye is comparable to photo( the strong light intensity that makes the dark lines rather faded) , then it is likely that the slit is too wide, Otherwise it is preferable to “to play” with the parameters of the recovery room to have less saturated images are sharper.
Anyway, from what I can see the surface it seems a good point , But my feeling is not a central hole ( rather, The center seems spherical ) but of a deeper annulus localized to 1/2 ray, but then again, serve less saturated image to better evaluate.
P.S. I am assuming that the images are in In focal
Hello and welcome to Luigi Grattavetro! Will be a pleasure, as well as interesting, know and follow the last stages of this process your.
I can not find a working link to Foucault Test Analysis.
yes I know, It is a rather long and complex search
https://www.grattavetro.it/download/
or directly:
https://www.grattavetro.it/wp-content/uploads/2015/11/fouc20b.zipto use ronwin2.0 , which I think is great, the win10, you must trade in the language settings, the point with the comma for separations of decimal numbers. At that point, the software works.
You can use FigureXp and also the Julius spreadsheet, but I prefer to use Foucault Foucault Test Analysis ( which moreover also simulates the Ronchi from the readings foucault ) not because of Giulio spreadsheet is not good, rather, maybe even better but I think it is too “open”, in fact it allows you to monitor any parameter, even those that for those not expert in this test, it would be better not to have to put hand and leave them in “automatic”. I see it more for “purist” Foucault test.
Anyhow, following the instructions of Giulio that will surely not fail, you'll see that it will not be so scary…
