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Beautiful work Mirco!
Leggendoti the first thing I thought of myself is that by breaking down the hill in the suburb 8-9 to bring it into the criterion Couder, you automatically gets up the 3-4 central, and you could have finished the mirror with the next correction.And I think it will be a dazzling mirror.
(You have no idea how the difference in sharpness of the observed details until you put the eye in a telescope with a mirror more than lambda / 4)
I have to agree Giulio, provided that the tool diameter is large enough to cover the areas from 3 to a 9.
But in this case Mirco going to use a small diameter, so you have to be careful where you run the tool center. In general a lower zone N ( decrease the radius of curvature or, increase the surface curvature ) , the tool center must run on the N-1 zone and consequently will rise ( increase the radius of curvature ) la zona N-2.If the diameter is large enough we trace back to your hypothesis by adding to the depth zone areas N + 1 – N + 2, while the other side we add the corresponding N-3, N-4, but in any case where the industry will run the center does not change its draw,
It's worth repeating because it is easy to fall in “trap”, at least the first few times that you use a sub-diameter, thinking that to lower an area simply work the corresponding sector.
Ciao, thank you both…
Massimo heck you're absolutely right, Fortunately you've got me thinking. I would have gone straight with tangential racing horse of the graph hill, blatantly wrong.
That graph shows the curvature and not the error profile.Given the two graphs then I would say that the tangential races I have to do astride the beam circumferences 70 e 148 mm and NOT those of radius 90 e 168 mm as I was about to do. Quite right?
Now even I evaluate the possibility of using a sub covering areas from 3 to the 9 as rightly suggerivate ...
Oh I forgot, if you wish to proceed with sub-small diameters, which of the three do you think I should use? than 200mm (50%) one from 115(28%) or the one from 80(19%)?
Some other tip on how to proceed since it is not then I've all this experience with sub? type stroke length, if you make it or not past planetary order processing etc.…I think the solution is to hand them ( at least in theory )
:the area 8 e 9 They are at the limit of tolerance, the 10 it must be “shopfront”, then the center of the diver must necessarily work within the area 8 e 9 which will remain as such at first.
in this way the external sectors increase the curvature and hence lessen the draw, while the internal increase it.
what diameter to use ? and a choice to make with some considerations:the excellent ( again in theory ) It would be that the sub would cover the industry Extension 6 to the sector 11, so that from 80.
In this way, with very short strokes and light pressure, You would lower drawdowns on 9 e 10 and something on 11 , similarly would rise flues of 8 -7 and a little bit of 6.In practice, the problem I think is another: the high number of areas makes it difficult to run the races exactly where you want. I want to say that after a few thousand strokes with the same tool can be perceived with your eyes closed where you are working with millimeter precision, but the feeling of “drift” with small sub it is typical when using a tool “new” or created for the occasion. The mirror suddenly becomes a football field where the certainty you never have to be “center field” or “three-quarters”, let alone if you want to walk around the course that is always at a certain distance from the offside line
therefore it needs a precise reference to locate the inner zone to 8 -9, everyone finds what they like, such es.disegnarsi with a marker areas on “rear” mirror, but without a reference to the risk of damage is high !
in this particular situation, move during the processing of one centimeter from the center of the area 8-9 It means bringing one of the two out of tolerance !
Also the difficulty of retouching is also that of the limited number of laps they need to so small corrections. The risk of doing laps “astigmatic” because maybe you realize you are too “wide” or stretch too much racing, and also high, if you work with the rotating floor it is certainly helpful, otherwise it takes a discreet eye.
Anyway, I'm sure you know better and to organize, once I made this correction I procederei Alike ( if you really want a lambda stratospheric ) about the zone 3.
Thanks for the suggestions Massimo…
I always draw me use with a marker reference on which to go to work on the back mirror, it is cheap, it takes a moment to do so and it is really useful.
I agree I also knowing that when you have to work out short-term there is a risk that some form of astigmatism, I therefore today the machine re-configured so that the rotating plane face 7-8 rpm.
With the mirror placed on the rotary table I run a session from 90 seconds with tangential rides astride the areas 8-9 and a session from 90 seconds over the area 3 without pressure esecitare.
I deliberately decided to run so short sessions to realize the removal rate of this tool before proceeding further… Hi everyone,
As mentioned in the previous post I made a very short session with tangential rides on horseback in the area 3 and zones 8-9.
But from the facts they tests not noticed significant changes so I proceeded to do other work sessions that consisted of 2 rounds of table with manual movement and 200 seconds on a rotating table, always with the same type of tangential racing (with a little more than at the turn of the zones work 8-9 compared to that on the area 3)And this new situation:
The outermost hill seems to be lowering and carrying within the tolerance trumpet.
Even the PV has risen rising to 12,60 !!! Now I'm considering what to do as the mirror, however, is already very good and I would not mess it up. So it's time to think very carefully.
Update on the method by which run the test
As we discussed with Massimo and Giulio, in the following form:
of how to increase the accuracy of the measurements, I have tried to improve the system by which I run the Hartmann test. The improvement does not consist in the methodology with which to run the test, that always remains the same, but in the fact that now I can easily and relatively quickly make and analyze 30 different measurements, from 30 different image for each position (intra right, intra left, extra right, extra left, For a total weight of 120 photo).
In doing so I have available much more data with which to perform the media, allowing me to increase the odds of correctly assessing the profile error.P.S: The test results set out above refer instead to the average of well 90 different measurements (then 360 images) !!!!!
See you soon…ciao
Great mirror and excellent work!!
I would say that it is also amazing the measurement method that you have packaged and adopted!!
Agree I think you take notes in the notebook grattavetro, in the course of this work, because I sincerely hope that in time you publish a detailed article ..which will be ONE of a kind, and not merely theoretical, as authoritatively corroborated by the simultaneous construction of your 405
An excellent mirror ! very good Mirco !:yahoo:
I would stop here, in case before any tweaks I would try to see if everything else is on the same high levels, I refer in particular to roughness and symmetry, seen that the sub-diameter ( especially in short sessions ) You can create some “collateral effect” in this sense.I agree with what was said by Giulio, a detailed article on the methodology of analysis would be very interesting and instructive !
Hi guys, thank you so much…
I think so too it is better to carefully consider everything before proceeding further if necessary…even if they are more than tempted to give another small blow riding areas 8-9, but I hope I can help myself…
The next pass I will be to repeat the test for 3 times by rotating the mirror by 120 ° in order to verify the presence or not of appreciable astigmatism. Maybe placing the mirror on his cell es perform the test on the stairs at home so as to make the test cell with the inclined approximately 40 °.
Then follow the Ronchi, even if a bad mark on the camera lens does not allow me to take pictures and I will then evaluate everything by eye.
Then evaluate the surface roughness with foucault or another method.
And finally mount the entire Dobsonian and take a look at the moon and planets…:good: …
Hi everyone,
It resumes after a period of absence due to other commitments they have made me long.I performed the tests again, in particular I made for three different positions placed them at 120 ° relative to one another. And this is the result of the reduction of the acquired data.
The form looks good and tolerance with respect to the policy and M-L appears to be no major signs of astigmatism. As for the maximum PV surface error it seems to be around λ / 12.
Regarding the roughness I still reservations, in the sense that I seem to perceive the lines of rhonchi that the surface is not really nice smooth, even if I have to do surveys, to have a clearer picture about. If noticing me there was the slight roughness, do you think there is a method to eliminate it (or at least mitigate it) without going to change the shape of the surface (since it is already very good). For one thing, perhaps with a soft tool so as not to be almost able to remove glass, but in any case such as to standardize the nanometric surface asperities?
Overall, however,, the vision of Saturn and Moon eyepiece seemed very good, despite the not perfect collimation of dobson that was a glimpse of the star-test in intrafocale a stellar disk area "missing", as if the secondary is not perfectly positioned and not intercepting the full degree of return light cone (this problem solved easily).
So in the end I'm pretty satisfied with the result, although it still has to fully understand the issue roughness and evaluate whether it is worthwhile or not to risk ruining everything to remedy a defect that might then not prejudicial remarks.
See you soon bye… Well ! seen the tests confirm the excellent past results I'd say you have a beautiful mirror ready to alluminare !
Regarding the roughness, the Foucault knife could better highlight the Ronchi, in any case when the mirror is really “wrinkled” leaves little room for doubt even with the Ronchi, therefore I would let stand, any intervention now alter the very good shape and also reached a too soft patina could create herself roughness.I only now post, and agree that the blade of the Foucault obscuring the entire surface without masks, very well highlights the roughness as a white mass of clouds on the background color of the source (but also displays any light dirt alike). So I would say that if you clean the mirror does not have white patches, roughness there (without going into interferometry…..because the scriptures say that any roughness would be magnified by a factor 600 thousand. What is the sensitivity of Foucault).
Hi everyone,
I resurrected this old thread, to update you on what has been the conclusion of work.
Finally after loooong time, I managed to bring the mirror to allumiare, and I thank you very much, the friendly Romano Zen, who performed the work I.But in the meantime, others to what is written in previous posts, I had been doing even small experiments both on the processing techniques, both on the optical test (P.S: I have always given priority to learning rather than the final result real why my mirror School, Otherwise I never touch it again made) that led me to grind slightly ("grit" 220) also the rear surface.
This operation, not very smart to do at that point processing, certainly it has slightly altered the final shape of the mirror, even if it lines Ronchi made the other day in Autocollimation were fine straight over the mirror, up to the edge.
So in the end, I can consider the finite mirror,
almost certainly not having the correction shown in previous posts, but certainly above the minimum required values for these magnificent instruments ...
I can not wait to test it in the sky ....
See you soon, Hello to all….
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