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Interesting experiment that of the video you posted:
I would say that it is an example of localized heating with a fairly intuitive outcome, since with the torch a point on the edge of the aluminum disc under Ronchi's test is heated, to show how the Ronchi is immediately distorted by local expansion, but returns to recompose itself in a short time, extinguishing the phenomenon.The thing is, in that case, the mass of the aluminum disc good conductor, it has a thermal inertia that quickly dissipates by convection inside, that strong localized heat.
Which would suggest that: if the glass is too slow to acclimate due to its poor heat conduction, but accompanied by a very favorable low coefficient of expansion; conversely, aluminum could be reactive too quickly, at the limit varying its surface shape by very high expansion, too fast, continuously and locally sensitively.
Which it probably could (seen the hand of NASA and Goddard) making aluminum preferable in some optical instruments of artificial satellites intended to travel far away or shielded, from astronomical radiative heat sources.
I would say a finish like that announced by the Goddard system of turning and subsequent polishing (“devilry” which reaches a roughness of 10 angstrom, that is, of only one nanometer) is the result of an exclusive cutting-edge technological patent, which I imagine also at the top of the application costs.
However, a decisively improving process, because it is able to bring the optical processing of aluminum into competition with that of the hitherto unsurpassed glass.
Excluding this innovative process, would remain the too high roughness obtainable on metals with the finest polishing process of all, known as lapping.
Which, however, does not go down as roughness below 100 nanometers high., which are therefore insufficient to obtain the minimum lambda / 4 error, which must count no more than nanometers 68,75.I don't think any electrochemical transformation is possible on metals (outside the oxidation) with displacement of metal molecules to plug the surface asperities, as occurs in the molecular transport of glass as silicate, caused by the simultaneous presence of water, care, cerium oxide (and aided by heat from machining friction).
Aluminum would be easy to work with, and shares its specific gravity 2,6 with glass. But the problem with aluminum is the very high thermal expansion compared to that of glass, even if at the same time it would be coolable with greater glass efficiency.
Moreover, On the topic of the quality of metal mirrors in general, I am reminded of some reading here and there on books and manufacturing reports for astronomical use, where two problems are highlighted which contribute to limiting optimal quality results, which instead are the prerogative of glass mirrors.
A problem is that the metal mirrors, even if they could consist of one pure metal, however, all physically possess a crystalline structure that glass does not present.
And therefore the crystalline lattice forms molecular stiffeners that make the response to the extremely fine abrasives of the extreme polishing that must be reached to reach the famous ones no more than variable and inconstant and unpredictable. 68,75 nanometer peak / valley error, which characterize the surface of a lambda / 4 mirror for visible light, which is practically the minimum entry level in the definition of "limited by diffraction alone" of an astronomical mirror.A further problem that also concerns it, and even more the limitation of the optical quality obtainable on a worked metal surface, is that only an electrochemical process takes place in glass (as well as merely mechanical polishing) called glass "molecular transport".
Practically, slowly, that process visually transforms the chipped edges of the craters left by the abrasives up to the grain under the microscope 800 or vice versa 1000, which during polishing are first seen to have rounded edges, and then decrease in size gradually “tappandosi” disappearing completely.
The work of the molecular transport process of glass is due to the electrochemistry that acts simultaneously on the pitch, which blocks Cerium oxide particles (very active rare earth chemical element), with the presence of water and silicates that make up the glass, that Cerium actively interacts with each other.
So much so that you should never leave the polishing by abandoning the tool for the weekend over the mirror, under penalty of appearance on the glass surface of iridescences, which are the visible optical effect of surface defects which, due to wave interference, cancel or intensify some colors / wavelengths, and must be removed with the resumption of processing, but which force an increase in the workload.
If I'm not mistaken, some ancient construction reports on Amateur telescope making volumes, they gave as quality obtained on some metal mirrors as a millionth of an inch … (maybe today we could technologically do better) however, that difference was thousands of nanometers compared to the necessary suns 68,75.
By working with glass, in practice, it is certain that the disappearance of all possible roughnesses, is is a matter of extension in time of work.
Very good Carlo.
At this point, all you need is the workbench to get started “round dance” around.There, too, there is a possibility of choice, whether to use the former mineral oil keg with multilayer lid to work standing up, or the bench like John Dobson to work seated.
Everyone has their preferences. I have always used the barrel because it allows you not to dirty the environment beyond the table itself, always easy to clean. And I was even better walking around it. While the bench is apparently more comfortable, but it is easy to dirty the floor .. What I would have found the veto on “landlady”(
), even though I've always done the work in the boiler-washer-ironing room.I'd say the right choice.
A 250 F5 alleggerito è un buon inizio, o F6 o 6,5 non allegerito è oltre che di buon inizio anche si facile e sicuro risultato di qualità.Welcome Carlo!
IF you already have some ideas, esprimicela, così ci aiuta ad aiutarti.Infatti costruire un telescopio Newton di tipo Dobson è il modo più semplice esistente. Cosa assai più impegnativa è costruire anche lo specchio primario, che peraltro può essere convenientemente acquistato nell’usato, e inserito nella struttura “do-it-yourself”.
I agree.
My objective…(from “The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm”) The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm, The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm, The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm, The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm, The difference will only be in having increased or decreased the focal length for the calculation of the values by a few hundredths of a mm, which at first glance has counter-intuitive meaning: which at first glance has counter-intuitive meaning (which at first glance has counter-intuitive meaning, which at first glance has counter-intuitive meaning, which at first glance has counter-intuitive meaning) which at first glance has counter-intuitive meaning, which at first glance has counter-intuitive meaning (which at first glance has counter-intuitive meaning).hello Henry
It is useful to compare the image obtained with a software simulation, It is useful to compare the image obtained with a software simulation 600 It is useful to compare the image obtained with a software simulation, It is useful to compare the image obtained with a software simulation.
It is useful to compare the image obtained with a software simulation, It is useful to compare the image obtained with a software simulation, It is useful to compare the image obtained with a software simulation “entry level” Lambda/4, which is the minimum threshold of already good quality because it is limited only by diffraction…(which is the minimum threshold of already good quality because it is limited only by diffraction) which is the minimum threshold of already good quality because it is limited only by diffraction, which is the minimum threshold of already good quality because it is limited only by diffraction 68,75 nanometers high., which is the minimum threshold of already good quality because it is limited only by diffraction. which is the minimum threshold of already good quality because it is limited only by diffraction, which is the minimum threshold of already good quality because it is limited only by diffraction, that with a few simple rules make the statistical elision of positive and nagative errors intervene.that with a few simple rules make the statistical elision of positive and nagative errors intervene. that with a few simple rules make the statistical elision of positive and nagative errors intervene, that with a few simple rules make the statistical elision of positive and nagative errors intervene, that with a few simple rules make the statistical elision of positive and nagative errors intervene (that with a few simple rules make the statistical elision of positive and nagative errors intervene, that with a few simple rules make the statistical elision of positive and nagative errors intervene).
Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut.
Finally, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, (Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut), Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut (Also keep in mind that it is not necessary to spend to have a Couder mask laser cut), Also keep in mind that it is not necessary to spend to have a Couder mask laser cut: Also keep in mind that it is not necessary to spend to have a Couder mask laser cut, Also keep in mind that it is not necessary to spend to have a Couder mask laser cut. In a practical as well as a simple sense “In a practical as well as a simple sense”, In a practical as well as a simple sense “high” In a practical as well as a simple sense.
The other way around, In a practical as well as a simple sense, In a practical as well as a simple sense, In a practical as well as a simple sense, In a practical as well as a simple sense, In a practical as well as a simple sense… In a practical as well as a simple sense.
In a practical as well as a simple sense, In a practical as well as a simple sense “"trumpet bell"” tolerances of the graph.
tolerances of the graph, tolerances of the graph, tolerances of the graph, tolerances of the graph, tolerances of the graph.
tolerances of the graph, tolerances of the graph, tolerances of the graph. tolerances of the graph.hello Henry, welcome back!!
you are heading towards a very good sphere!you are heading towards a very good sphere.
you are heading towards a very good sphere 93 years (from the 1927) you are heading towards a very good sphere.
you are heading towards a very good sphere, you are heading towards a very good sphere, you are heading towards a very good sphere (you are heading towards a very good sphere)
Hi Guys!
The virus hasn't caught me yet, as I hope of you.
But for over seventy I stay at home and mess around “multitasking” , how to prepare to mount (never done in my life) a new rear bicycle wheel for my Graziella folding type with 20 wheels″, installing a three-speed Shimano hub gear, and work “Corali” etc.Massimo you say [Quote]
Therefore it will be necessary to understand how to intervene on astigmatism with a sub-diameter. I must say, however, that intrigues me, I have never worked on this type of defect, and I still have no idea of the solutions, if not that ( all to be verified ) to start working locally according to the tool diameter on the mirror center, until it reaches a central spherical area and then gradually extends outwards. Mah…
[Quote/]I know well (in the sense of only having read it correctly) the local correction system of astigmatism with sub-diameter tools (although in any case alternating with passes of uniform full diameter) described by Jean Marc Lecleire in the French book: ACHIEVE YOUR TELESCOPE.
Of course it is a dangerous system because it is likely to create zonal errors, compared to a classic work with a full diameter tool to return to the sphere. But if experienced by you, it will certainly bear good fruit. Why then, how do you say “when i go…this vò”!As for the full diameter tool, I remember seeing pictures of Mr. MAXUTOV himself, brandishing a large tool, but light because built with plaster “thin”, anchored to a large diameter plywood board, drowning I think the usual mesh and screws.
I try to find out if I find anything on 3 historical ATM volumes of Ingall.See you soon
GiulioJean Marc Le Cleire's French book explains how to correct astigmatism with local subdiameter processing.
In practice there is astigmatism when the mirror has two meridians with different radius of curvature: The focal closest to the mirror is called the tangential, and it is the one with the shortest radius on which you can scratch; while the most distant is the Sagittale.
It is therefore a question of identifying that meridian (that at the star test would present the stretched image in intrafocal), and mark it with a marker.
Identification of the tangential meridian, on the book it is described with the foucault tester “DEL FILO – (wire test sul Malacara) modified with the slit made rotatable; to which it is possible to remove the blade and replace it with a vertical wire of about 0.1mm diameter which can also be rotated by hand.
The tester is then brought with the blade to the center of curvature of the area at 70% diameter, notoriously the least distant from the sphere in a mirror in progress; remove the blades and put the vertical wire in its place.
In the area 70% a large letter will appear in the mirror “BE” upper case whose circle and straight line are the image of the wire centered on the area 70%.Then turning the slit and thread, the letter Fi also rotates, and one should be aware of the possible presence of astigmatism, when the letter FI begins to decompose into an S type with a spiral galaxy type.
Then rotating the slit and thread in the direction of curvature of the spiral, it will be reached again when the letter FI is recomposed, when the black diagonal will arrive on the longest focal meridian. which consequently is perpendicular to the workable meridian to be marked with a marker.then a +45 and -45 ° astride that workable tangential meridian there will be two imaginary diameters that will divide the mirror into 4 quadrants, the two straddling the offending meridian are those that can be worked with small diameter tools, to lengthen their focal length and unify it with others 2 major focal sectors, doing zigzag runs of small amplitude describing in each of the 2 dials a capital letter T.
The difficulty is that in any case it is necessary to arrange a full diameter tool with which from time to time it is essential to regularize the work.I don't remember what book I saw pictures of Mr. Maxutov brandishing lightened tools in multilayer disc (specific weight 0,4) used as support and reinforcement of the thinner large diameter plaster (specific weight 2,6).
I'm looking for if I can find Maxutov, and I will translate and send you the pages of the book
Giulio nightYou say:
“By the way, do you think we can recover the dowels of the previous tool which, among other things, are also partially adapted”?And, you can retrieve them by cutting them around with a hot knife, if you can detach the squares you can also glue them on the tool you will make, heating the back of each picture with a candle, and placing them on the tool with a slight flat pressure (with for example a cap) so as not to deform them, or deform them as little as possible. In that case, however, the adaptation would put them on a par.
Excellent passage of plaster on concrete (otherwise you should pour the plaster on a mirror heated in a bain marie in order to reduce the distance between the hardening temperature of the plaster, from that of the mirror, which is still a risk).
Hello guys. I point out the interesting assessment / verification (in French but translatable fairly decently with the right mouse button, su Google Chrome) on the rigidity of the meniscus mirrors, in comparison with those concave planes of equal thickness at the edge, performed by Pierre Strock, passionate nuclear engineer self-builder of French telescopes.
