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Well, I take back everything I've said so far…
If you look at the whole correct field tolerance in the distance between primary and secondary loooong it becomes more thrust than it seemed when they looked only axial aberrations.
Then, eye I understand that surely must keep well below the waste millimeters compared to the ideal fit, worth a rapid decrease in system performance…It seemed really strange fact, that there might be such a large margin in the longitudinal positioning tolerance of the secondary…
LUNA TEST
Last night a beautiful clear sky, regardless of the mirrors still alluminare
, I mounted my faithful and very little webcam behind the eyepiece, to share with you “the first month” and see if you can make some assessment.Eyepiece 35 mm ( I think ) homebuilt with an apparent beautiful wide field to the real field resulting 0,7 degrees, the video goes to “shots” because the webcam works only 15 frames / sec.
there is a drop in brightness at the edges, vignetting that should not be there, we are around 20 mm focal plane, I may have done something wrong in the position of the lens hood, but this is easily remedied.
Apart from the quality of the video, but that's normal with this webcam from peanuts, it seems to me that the image is in focus for the extension of the moon in the middle of the field, a blur beginning is known in the vicinity of the edge, in accordance with the presumed correct field 0,5 degrees… I do not know if you agree.
Some magnification in more.
Eyepiece 10 mm (225 x ), one lousy Vixen NPL that the ugly flaw of having a curved field,
which to me to be terribly bothered, It is a known fact “enlargement” the image at the edges.eyepiece 15 mm with the addition of a “barlow” autocostruita, small zoom the webcam to center the image should be around a focal length equivalent of 6-7 mm for the eye. ( 350 x about )
This is what I see at the eyepiece, actually with the eye you can see better and more than capture a webcam, ( and it will be even better with illuminated mirrors ), but to make the idea is fine…
At this point, let us not miss anything, us “dress” by astroimager and do what needs to be done, we add and align the individual adjustment frame, condiamo all with a little’ in Photoshop, we rotate the image and here served Waning Crescent.
Well I think that the results are excellent given the experimental conditions of the situation!
I realized now that I put the moon “mirrored” ! with all these reflections I have not understood what is the image I see compared to the actual, I have to try it on Earth
guys, you think, It must be supported as the secondary ? silicone on the back ? angle for support on the reflective, and how many ? a 120°, 90°… or other solutions ?
another question: all my secondary support, including lens hood, It is a block “closed”, in the sense that there are no openings ( obviously wineskin to that for reflection
) and I did not provide for any machinery for the thermal balance / boundary layer, and from what I've seen around, even the commercial telescopes are like that…why for the secondary the problem does not arise ?
I could not advise.
The reasoning I can do (and that he himself is “two-faced”), is that the tube which contains the secondary, fixes it from contact with moist air, and then, It helped also by the external display to the truss, It does not seem possible fogging. Unless, the absence of a vent hole in the upper part of the secondary shelter, may be the cause of stagnation that could perhaps disturb, and unless the long exposure to cold, does not transfer this to the secondary by conduction through the support, in that case the three silicone balls may be of glass isolating the aid.But I realize that I said “everything and its opposite” (….as the infallible predictions of Saluzzo time, which translated from Piedmont recite:
“If Viso has hat, or make you ugly or beautiful will; Ma
if Viso has nothing at all, or will do good or do bad”).I still do not understand
The star test I always say I have a residual spherical 1/4 The Lambda.
However, the stars seem to point and are on fire like a dream, but when to step extrafocal intre, the shadow of the secondary is much bigger: spherical system undercorrection, no rain ! ( It means that the secondary is sovracorretto )Then I tried to touch up the secondary, trying to take the shape of the gauge more accurately.
Now the fringes are even straighter than before, at this point the difference with the caliber is less than 1/4 The lambda.
Run again the star the spherical test not only has not diminished, but it seems even increased…
I tried again with the Ronchi grating instead of the eyepiece: with a little’ fantasy can be seen in intra-focal bands near the edge which tend to widen very little, un'inezia, but it is possible that I imagined, brightness and very low.
At this point in my opinion there is only one possible explanation: the size is not sufficiently corrected !
How is it possible, since the Foucault test
indicated a lambda correction / 9 ?Already… Foucault test, on a mirror F3 to watch case is sovracorretto in the peripheral zone, in case there were any doubts about the validity of this test with short focal lengths.
So you could do two things:
1-re-appear with the caliber of caustic tests ( I do not even think about that ! )
2-undercorrection a force on the convex edge of the lambda / 4, holding the gauge as a reference.I think it is groped by this way, It means having to increase the curvature of the edge ( to reduce the correction, you have to shorten the radius, hyperbole is more sovracorretta “flat” on the edge )up to arrive to the fringe part of the terminal near the extension of the next fringe, roughly like this:
These days I went back to work the secondary, with a series of tools is a circular crown that sub-diameter.
I want to understand how the figure is to be built, the pros and cons of the techniques and especially the precise interpretation of Newton's fringes to decide what / where / how / how many posts of corrections should be made according to the figure interferometric.
So far, the correction interventions, even if they led to the result, They have not been made with the knowledge of what I was doing , but rather trying things.
From here , My numerous errors including the edge and the star replied suboptimal test.
Now I am studying the matter wisely and I must say that we would have to write a lot ', the “World convex” it is a different story than the concave, but if approached with the right methods can be planned and carried out without too much difficulty, also for conical constants “exaggerated”.
The main difference is in setting mental, it is a psychological problem that technical, but once it changed the way we think everything becomes more natural.
A small example: Concave in the past we use the court to prevent the edge retorted, convex in the past generate the court ! and the reason is quite obvious, just that to get there you think so “convex”
So I brought back the hyperbolic figure of a couple of step K, I started arranging the edge retorted ( even if it does not need because it is hidden by the hood )and now I'm back to building the project approach K, also to verify that the methods that I have developed is correct.
I want to get to a star proper tests , to do this we must have a hyperbole that differs from the likes of a certain value (lambda/4) without changing the central and end points of hyperbole.
Then we need reliable and precise techniques, together with the exact interpretation of the fringes of Newton, but this way we will definitely talk about it in the Blog. For now here is the job status, with the edge retorted that is very slowly returning with the application of appropriate technical, obviously without losing sight of the figure hyperbolic.
“gift” Christmas for the secondary: I removed that nasty edge retorted, even though it was irrelevant because the external area of useful reflection.
More than anything it was my personal verification of the effectiveness of techniques with sub-diameter on the convex. By the way, do these corrections is far from simple, the edge of a hyperbolic thus deformed ( k<-5 ) si gestisce con difficoltà ed in generale più lo specchio è piccolo difficile lavorarlo, perciò credo sia sempre preferibile utilizzare un vetro "oversized" per il secondario infischiandosene del bordo, ma se proprio vuole correggere bordo ribattuto, meglio farlo quando ancora lontani dall'iperbole finale. Ora devo finire di riportare la superficie alla forma corretta, al momento deviazione massima dal calibro circa 1>
Bravo Massimo! Experimentation is always attractive but very, very challenging.
Murphy is right when he says that an expert is someone who “It has already committed every possible mistake in a restricted area of knowledge”, why (in the absence of precursors divulganti), without those mistakes you can not learn on their own the right path.
This is because the common attitude of that road already knows, is usually jealously and selfishly, keepers of the secret. This attitude is the exact opposite of the principle of sharing and dissemination of “roads” already well tested, who is the team spirit of us Grattavetro.
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