This article is divided into four parts, in which it is fully shows the shared discussion forum from 20 February 2014 to a 9 June 2014, with the glorious completely manual realization by “Massimar”, a mirror Newton diameter 300mm focal ratio F 3,8 with excellent quality of surface roughness given by peak / valley on the glass less than one-sixteenth of the wavelength (Lambda) of 560 nanometers of yellow-green light that the human eye is more sensitive, corresponding to an optical quality of at least lambda / 8 reflected wave.
All this of course respecting the all-important Couder criterion, which states that (..in order to get the perfect canonical diffraction image giving maximum quality and contrast in the images provided by the telescope that will mount that mirror), the reflective surface of the mirror must be such that all reflected rays converge within the "diffraction notch" (also called Airy radius), which in fact, for the mirror in question, is a little disk in diameter 2,6 thousandths of a millimeter (microns) which is located at the distance of 2280mm by the mirror itself, equal to the focal length of 1140mm.
The teaching and educational importance of the discussion, for those who want to have an excellent example of how it carries out a good optical work, It is absolutely made unique by the wealth of detail in the description, both budgeted corrective actions from time to time, and that the results (good or bad) obtained, from the fixes made to finalise the processing of that superb mirror.
The importance cited is coming from the fact that all the numerical data given here, are all you need which can be profitably typed within any program for evaluating the Foucault test, in order to study and active testing of the variations of the shape of the mirror surface, until its fulfillment.
Part 4 of 4
Re: Parabolizzazione mirror 300 F 3.8 A good method to verify the well astigmastismo is to use the image of a small steel ball illuminated by a focused light source. If you book on page Texerau. 86 (fig. 40) English edition is clearly indicated how to proceed to test astigmatism. It may also be present astigmatism, probably caused by the use of sub-diameter without using a rotary table. That's why I insist on the fact that with sub-diameter is okay to use this device. For micro areas of retouching must proceed according to me even with a tool to be 25 – 30 millimeters in diameter. Courage, we end this mirror ! |
Re: Parabolizzazione mirror 300 F 3.8 The “sacred text” I got it, for sub 30.. I'll do that too :) |
Re: Parabolizzazione mirror 300 F 3.8 @morfeo: it's time to jump. ………the path is slow and gradual (except for doped as massimar :D) but it returns a great level of knowledge and awareness of what otherwise miraculous happens inside of a mirror. @massimar: I have not yet got to the point where you are you, but the nose is to ask me: you've tried to slow down with work and increase the frequency of measurements? I instinctively reminded of the doubt that already at least a couple of times you've crossed the encroaching right point in the opposite direction. ………….but be careful: mine is just a modest sensation! |
Re: Parabolizzazione mirror 300 F 3.8 Quote:
Is’ vero, But only the first time , and they had to go to the ball. Not this time… coming from… I filled the tread of charts and ronchigram :) |
Re: Parabolizzazione mirror 300 F 3.8 Giulio, I have some doubts about Foucault test, but also the certainty that you will know them melt like snow in the sun :D We are trying to do precise measurements in tenth of mm and beyond, but then if we think of this ladder of magnitudes, there are some inevitable differences setup from one session to the next (after removing the mirror and moved the apparatus ) which in my case I am: – it is impossible that the source is always positioned at the same distance from the mirror and consequently the distance between the source and the blade, both longitudinal and transversal will never be the same. – the mask I printed on cardboard and I cropped hand, as far as can be good in DIY it is impossible to cut out areas with precision and that you can not have the certainty that the mask and the mirror are positioned each time with perfectly coincident centers . I wonder how these aspects do not affect the accuracy of measurements, in other words, how do I know that the measure I'm reading compared to that of the previous session, does not have a component that “stretching” or “restricts” the same extent, due to the different setup ? :hmmm: |
Re: Parabolizzazione mirror 300 F 3.8 I guess all of you scratchers will be built by you the Foucault test,or you may find that?Instead Ronchi to believe that the apparatus is simpler nó? |
Re: Parabolizzazione mirror 300 F 3.8 ciao morfeo, there is a tread sull'autocostruzione of an apparatus Foucaut / Ronchi made by a certain massimar, so knowing the type would not trust a lot… :D, joke, fortunately not all of his own making and therefore works well. otherwise even on stellafane site there are great projects to build the tester at home. |
Re: Parabolizzazione mirror 300 F 3.8 Systematic errors you listed, (otherwise the setup position of the measure due to mirror displacements or tester; Different mask centering on the center mirror) They are actually always present. It is not a mistake to consider the difference in absolute value of the drawings between sessions measurement, because that which is authentic are the differences between relative rather than absolute values of neighborhoods, works , beds to the same point of machining, They should always be identical or very similar. While the longitudinal distance between source and blade remains by definition identical (because the fire does not vary if we do not act with the processing, species in the central area). (With very low focal openings, but do not know how, I know that testers are used with source and integral blade). The detect draft values to the hundredth of a millimeter, (like I do, I installed a micrometer on the longitudinal adjustment screw tester), I highly suspect that leave things as they are, and I may be wrong…. but most likely, instead of detecting inaccurate values to the hundredth, More should be done to detect the values much more easily accurate to one tenth, However, making the average of at least two sets of center-to-edge and vice versa readings.. This because, (and I say so to your final question) to a lot of light …."Relativity" operational (that it does not disturb grandfather Albert), the only truly valid way to "medicate" read errors, it is to use the average values, that eliminate the exaggerations involuntary both underestimation of overvaluation. (similarly to those who make extremely detailed astronomical photos by superimposing many pictures ciofeche). It not for nothing is harder than any craftsman will certify a lambda value derived from a Foucault test. Anyone with a mirror can see for themselves a unique lambda ever (and it is indicative, but not technically correct, as you might think, giving greater precision, Foucault running a test on two or more different diagonals, because it would be a principle of evaluation phony pseudo RMS). (The imperfection is unfortunately the strong eddy testing. But it is the only popular means to see with the human eye, and groped to correct, imperfections on the glass of a few millionth of a millimeter). |
Re: Parabolizzazione mirror 300 F 3.8 To minimize measurement errors with a short throw mirror is almost compulsory to use a Foucault slitless tester, ie with the led placed immediately under the blade, obscured the 50% of his silhouette. Doing so will minimize the problems due to the light source placed off-axis. |
Re: Parabolizzazione mirror 300 F 3.8 Thank you Giuliot :ok:, clear and exhaustive ! astrotecnico, I wondered how the temperature could also affect the test run ( as well as the processing ) and whether the test can do immediately after a session or whether it is better to wait some time. ….. update mirror:  Click on the link to enlarge http://s26.postimg.cc/itslp0oih/Untitled_1.jpg and for those who do not know them and it is curious to see how they are made the zonal errors of sub-diameter, look at the series of concentric crowns in this image:  Click on the link to enlarge http://s26.postimg.cc/m866reujd/image.jpg I did a quick test of Foucault only to see overall draft, what depth I will do tonight. Now I stopped to figure out how to dispose of “signs” tweaks without changing the curvature of any area. How you do it ? :hmmm: |
Re: Parabolizzazione mirror 300 F 3.8 Quote:
With an excellent mirror vetraccio, consider doing retouching and put the mirror on the perch and postpone the trial to the next day. An anecdote concerning, It is that I happened (the first times), to put the mirror with bare hands on his perch, ready for the post-correction measurement, and to see again two hours later (through Foucault tester, without Couder mask), the turbulent but detailed imprint of my hands on the edges where I had grabbed hours before…!!. Another time, even though I had expected the following morning, I noticed a terrible turbulence…I discovered was coming from the house keys that I had inadvertently deposited on the table , just below (but under a lot ..) the alignment axis between the mirror and testers. with hot :mad: the nanomertri become micrometers! |
Re: Parabolizzazione mirror 300 F 3.8 you can see the light at the end of the tunnel ! I tried to even out the surface with two sessions 15 min lightweight ( only thrust without pressure ) passate COC sub 125 that a few tweaks they still brought, luckily in the right direction ! ( I am called by my party “with that of ..” ) Ronchi test after the sessions ( hot )  Click on the link to enlarge http://s26.postimg.cc/goc2zqp7d/r12.jpg Below ( always “hot” ) series of two measurements with Foucault: ( I have insisted that will remade ” cold” ): media = 0.92 2.70 4.90 6.88 8.97 Report Foucault Test Analisys:  Click on the link to enlarge http://s26.postimg.cc/y5g6uupzt/wp4.jpg Chart ML:  Click on the link to enlarge http://s26.postimg.cc/hf4t5irkp/ml5.jpg Report Spreadsheet Giuliot:  Click on the link to enlarge http://s26.postimg.cc/il8t4bfvd/Tes…_8_3_05_14.jpg Quote:
 Click on the link to enlarge http://s26.postimg.cc/jxqi67dax/r13.jpg
|
Re: Parabolizzazione mirror 300 F 3.8 They are in Vittorio Veneto around in camper, and I have no easy way to see the images on the win-Phone…but I see that c’ It is a good improvement of the figure, and also the lambda, where one of the “minimum wage” It is already there, out of the’ door waiting. I add that I am very happy, and shows that you have understood how the cabin! |
Re: Parabolizzazione mirror 300 F 3.8 Hello Giulio thanks , fa’ have a nice trip… |
Re: Parabolizzazione mirror 300 F 3.8 massimar about the apparatus of Foucault's true that we said that with cleavage is fine, But then there was talk of a mirror F5. In fact, The norm, a Foucault tester of this type is good for mirrors with focal around 5 or higher. If you test mirrors with shorter focal length it is good to use a slitless. With all this I do not mean that Foucault traditionally done with a fixed light source and slide does not fit. The problem is always to have the nearest light source as possible to the blade, partially overcome by the use of LEDs in place of the old sources of light. For the corrections you've made keep in mind that you are very close to a good result, so now you have to act very cautiously. Very important is the proper fit for the patina, then, in my opinion, you have to go in this direction. Also you have to use the patina with the right hardness. To do this, I usually use very frequently immerse the patina sub diameter in water at the right temperature temperature. In any case, given the results you're getting with the focal 3.8, despite your temerity :D I can only compliment you ! And finally, since your first mirror Short Throw, do not push too hard to get the most. Please note that even professionally tend to accept compromises ;) |
Re: Parabolizzazione mirror 300 F 3.8 Quote:
Thank you astrotecnico , In fact, what I now want to do, before groped with other fixes the improvement of the figure, ( I do not want to abuse of fortune ) It is a good “makeover” the optimization of measuring instruments, I want to develop the whole of Foucault setup, Also taking a cue from the last discussion of the Couder mask'm preparing the file for me cut the mask on plywood laser cutting ( Today these chores you do them with a paltry expense ) and then I want to replace the meter with a longitudinal bar “adjusted” to have a more linear displacement can. did this (Also awaiting the return to “smooth writing” of Giuliot :hello:) I repeat the measurements and see if the results are confirmed or not, then decide on any adjustments. Meanwhile, I tried the mirror on Dobson ( last night he finally sees the sky ) and I must say that is not bad, pinpoint stars and moon very detailed despite turbulence, Also missing the alleged defect astigmatism observed on Mars now appears with the hard edges ! , But just outside the center of the visual field , in the suburbs I still see a little’ spherical as well as to the physiological coma. |
Re: Parabolizzazione mirror 300 F 3.8 Well the mask made of plywood: It is much more rigid and reliable. The ML diagram confirms what you saw on the pictures. So at this point you really are very close. I do not insist too much in correcting the center, even because, As you well know, It does not contribute much to the image formation. I would act rather on the periphery. The coma Notice, by one so open mirror is normal, while the spherical is obviously improvable. But I repeat: not to push too. Try to make a well-mediated quality. The next time you go over the mirror. Both are more than certain that it will do more :) |
Re: Parabolizzazione mirror 300 F 3.8 And, astrotecnico, I'm trying to figure out how to take action on the peripheral zone. Certainly the well-mediated quality would be the most satisfactory result, In fact I am convinced that the results of excellence are not affordable for people like me who are beginners, and I speak not only of experience but also of “weapons” understood as equipment , materials, Measuring devices, work environment, I believe that every aspect of processing ( operator included ) It must be of superior quality to a higher result, less than real lucky breaks. for the next mirror… I'm already thinking :) , contrary to the truth I think since I started, but in order to do what I want, I must first learn to work well short focal lengths… |
Re: Parabolizzazione mirror 300 F 3.8 On the outskirts you have to intervene with a sub diameter but very softly, with short sessions and many measures. I believe you want to do a Cassegrain :hmmm: |
Re: Parabolizzazione mirror 300 F 3.8 Absolutely yes !!! , astrotecnico now that's great news ! :ok: p.s. I imagined that you would have guessed the Cassgrain… :) |
Re: Parabolizzazione mirror 300 F 3.8 Back to the sphere III I tried to improve the figure, the intent was to bring tolerance even in the peripheral zone. With slight COC races and W sub 125 mm, outdoor areas have subsided along with the center which has become deeper, what little was enough to bring the parable ( in its overall draw which was already at the limit ) beyond the “point of no return”, Now I'm ( quasi ) back to the ball, no problem, It will again try again the approach to the dish and how it is said… “there's no two without three” ! As you may have guessed all , the blame for this attempt gone bad is not my, But say Giuliot, :in: it being around with the campers left me alone with Mr.. Foucault who, notoriously, It is a tough guy who does not like the company of strangers. :)…I kid Giulio, about when you come back ? |
Re: Parabolizzazione mirror 300 F 3.8 Expensive massimar you did not act with the 125 to regularize the area, but with a smaller tool, without using the past to W. You had to work out center, laterally, passed forward / backward and even planetary, only the affected area, with small tool, with light pressure, controlling continuous. This tended to dig a circular groove leading to the measurement zone. Then you had to stabilize the edges of the groove, spianandoli with a tool even smaller, looking for a good compromise. It covers well the films of Gordon Waite. |
Re: Parabolizzazione mirror 300 F 3.8 And astrotecnico, now I get it, :spaf: |
Re: Parabolizzazione mirror 300 F 3.8 Taking the parabolizzazione… part III :) Since I have so far used the same patinas with the same techniques, I believe that the differences are only to be attributed to the different abrasive. These images of Ronchi, I do not know if you give the same impression.  Click on the link to enlarge http://s26.postimg.cc/rskyqx63d/Untitled_1.jpg astrotecnico, waiting to see how I'll pierce the mirror, I go on with parabolizzazione, or is it better to stop and prepare ( first of all psychologically :D) to make a hole on the glass ? |
Re: Parabolizzazione mirror 300 F 3.8 Clearly, the iron oxide is probably, Also today, the best polishing agent, though, as you well noticed, It is slower acting. You have done well to decant, because really pure find it is rather difficult. This is one reason, apart from the rapidity, so professionally using cerium. With regard to the hole you have to do it right away, and in this case I recommend to pass completely through the thickness of glass, then Ritchey method. First, however, it is crucial to determine the diameter of the secondary you want to use and then be able to calculate, with a simple mathematical relationship, the diameter of the hole to be made on the primary. For the operation must be built a suitable support for use with a drill press. Use of this is crucial. As it only takes a modest drill, nothing professional. It also fits a normal manual electric drill mounted on a suitable column. The only important thing is that he must have the electronic speed control. |
Re: Parabolizzazione mirror 300 F 3.8 I think one of the hardest things to accomplish with precision, It will be the negative of the secondary focal, So I figured an intermediate focal between f12 and f15, so as to also have leeway. I would think to do this:  Click on the link to enlarge http://s26.postimg.cc/k8wh2m2ah/cas1.jpg So a Cassegrain f 13.5 from 4000 mm focal length with the secondary from 85 mm diameter negative F4.9. interesting as with these focal pure Cassegrain and RC tend to the same values, in particular the primary RC is almost parabolic, even if it would make little sense to an RC f15. Another curiosity: previous parabolizzazione, abandoned for exceeding the parable, It would be a Lamda 4 a primary RC F12 ! |
Re: Parabolizzazione mirror 300 F 3.8 In fact, the biggest problem of the Cassegrain is the realization of the secondary. The project we have calculated ATMOS can definitely go. As a first test is good to keep a total equivalent focal longish, trying not to lead to values exasperated conic constant of the secondary. For your observation on a RC I would say it is fair to say that it makes little sense if done at F15. |
Mission accomplished ! Summary: Yesterday the situation was at this Ronchi:  Click on the link to enlarge http://s26.postimg.cc/76e7sqbrt/Picture_1094.jpg The Foucault test gave me the zones 1 e 2 correct, while the remaining were still high, at that point I was working the outside area with past chordal sub 125 mm centered about the area 4, slight pressure on the outer edges and quite long runs. Is’ It took just half an hour of actual work divided into three sessions to get the desired result: Ronchi Test:  Click on the link to enlarge http://s26.postimg.cc/mwup8m5nd/ron_10.jpg Readings Test Foucault repeated until the physical exhaustion !!! Charts:  Click on the link to enlarge http://s26.postimg.cc/sathg5vdl/image.jpg  Click on the link to enlarge http://s26.postimg.cc/e5noecmc9/tr_ab.jpg Calculation Sheet Giuliot with all the test parameters:  Click on the link to enlarge http://s26.postimg.cc/o0etkkqah/01_06_300f3_8.jpg To be picky there for you to fix a little something, the grooves of the circular crowns are not entirely absorbed, the edge should be slightly lower to remove it from “borderland” ML of the graph and to have a constant even closer conical -1 , but I believe that even the scratchers experts will agree with me when I say that it is better to stop here… before doing damage ! I tried the mirror on Dobson, nothing to say… one can see , I do not see spherical, I see no astigmatism, I can only see an apparent coma at the edge of the eyepiece, but for this I can not help it. Astrotecnico, I could not puncture the mirror before finishing parabolizzazione, It looked a little’ to give up something I had started, I first had to complete it as it was inizata, only for the satisfaction of completing a job that has been long and arduous. Now I can think about the Cassegrain, I make a hole in the mirror and if I rifigurarlo , patience… Mica did not think to stop garattare ! |
Re: Parabolizzazione mirror 300 F 3.8 Hi Massimo. I only read what you wrote not being able to see the photos (I am in Normandy on Juno beach, in camper, for the “D-day”). But now I'm sure whatever you do, It is done with the criteria should. |
Re: Parabolizzazione mirror 300 F 3.8 So guys, certainly I do not hide my satisfaction, a 300 mm F3.8 lambda 8 It is the best I could expect, indeed beyond my expectations… the comments made last night they gave me the confirmation that the mirror must not be touched at all and left as is ! So as usual ( eh ,eh second mirror to find myself already saying “as usual” :in: ) thanks to those who made it possible for me to do all this. Thanks to Forum, only one in Italy where you can access such a large amount of information and so selective in which you have the opportunity to interact with industry true personalities. Hello and remember that there is a scratcher in all of us !:D |
Re: Parabolizzazione mirror 300 F 3.8 Great massimar ! I would say that at the moment does not suit you groped improvements. So it's likely that when you go drill then you still have to touch up. Now awaits the history of the bore and the secondary. It will be a great adventure ….. :) |
Re: Parabolizzazione mirror 300 F 3.8 astrotecnico, This is an adventure that aspect since I put the first spoon of 80 on the 125 mm !:D These days I repeated the test Foucault. There is a certain “oscillation” results and I do not depend ( except in small part ) by inaccurate readings. It must be said that the maximum variation that I found on the measures is 1/10 Mm, but that is enough to change the overall report significantly. I ran the star test which tells me ( if I understand correctly ) that there is a slight spherical, as the shadow of the secondary it is significantly different in size moving from intra to extrafocal, although the diffraction rings appear similar. Ronchi test, performed with the reticle eyepiece, shows straight beautiful bands until I see two or three. With a single central band, in extrafocale, there is a slight curvature to decrease the amplitude of the band towards the edge. Observations of the Moon and planets instead, repay all the work done, even if the mirror is not aluminized. |
Re: Parabolizzazione mirror 300 F 3.8 The Foucault is normal …(well at least to me…) dia that margin of assessment. But when you're definitely more than lambda / 4 the difference you see just about difficult subjects. Even if it seems impossible to be of this magnitude. Which, alone, worth the effort of the work performed. |
Re: Parabolizzazione mirror 300 F 3.8 Great massimar, complimentoni for the result, remarkable…:ok: |