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Hi everyone, I'm Stefano and I live in the province of La Spezia. I am passionate about astronomy, of physics and physics applied to astronomy
I am an incurable geek, both computer and practical and I love doing things… build, design and so on and so forth. I am fascinated by the world of self-made telescopes, quality optics obtained from a simple blank and I love the theoretical and practical research behind these technological adventures.
At the moment I don't have any important instrument other than a telescope 20×50 and a pair of binoculars 7×50 but I happened to look into other people's instruments and be amazed several times.
I own a 3d printer, I delight in electronics and occasionally do some circuitry. I use Solidworks for the 3d drawings with which I design my ideas. I would like to become a grattavetro because completing such a project would give me enormous satisfaction. I could have bought a commercial telescope but in life I have almost always preferred the journey to the destination because in the journey you learn beautiful things and enrich yourself. I hope with your help to succeed in the enterprise! I would like to start by scratching a 300 f / 5 to be mounted on a Dobsonian type project even if perhaps it would be preferable to start from a 200 f / 5 or f / 6 which would give me more peace of mind and something usable directly from the backyard (maybe you will help me evaluate).
At the moment I'm looking for the right glass and since haste is always a bad advice I will take my time to make all the necessary assessments. In the meantime, thank you for accepting me and seeing us again in the discussions
Hi Stefano, a very warm welcome from me, here in the forum…
I didn't own a telescope when I started scratching either, and even today the only one I have, that's what I built myself, and I think that was a big incentive for me, since if I intended to observe something, I had to finish the job…
Anyway returning to us, I tell you that both of the types you mentioned, the 300f / 5 or the 200f5-6 are feasible as a first experience. Clearly with the 200 easier and faster to build than the 300, something that you could use to your advantage to learn how to manage the various processing stages, and then try your hand at already a wealth of knowledge, in the realization of a more demanding project.
But, as I told you also the 300 f / 5 you can do it very well, also because from the presentation you made, I understand that you are not one who gives up that easily… Then you also have to see what you would prefer to observe, se planetario o deep sky, and the quality of the place from where you would usually observe…
Thanks Stefano, the more we are, the more we can share, so welcome!!
Let's say that like you I'm a super geek too,I haven't made a mirror yet,
the search for suitable glass took me months.propio in these days I was able to find
two blanks suitable without fainting in euros. I bought the abrasives…
See you soon I live inland a 5 or 6 km from the sea… it is not really isolated countryside but not even a city and not having much experience I would not know how to assess the level of light pollution. The luck of Liguria is that in less than half an hour by car you can go from the beach to the mountains above 1000 meters with a pretty good sky. My ultimate goal would be to have something usable at home and something large in diameter to use for targeted outings. The planetarium interests me but in order of priority I definitely put in front of the objects of the deep.
Once I have clear which measures to choose I will start with a PC design of the instrument as a whole. As soon as I manage to get the glass, I will put the PC aside and start with the actual project Hi Stefano and welcome also from me.
Mirrors with diameter 200 or vice versa 250 or 300 they are all within the beginner's reach, so the choice is not wrong whatever you decide to make.
The 250 lends itself to making the usual virtuous “middle ground” which is very valid both in the deep and in the planetarium.But you should consider that with a 250 F5 or F6 is observed from a seated position, while for a 300 you are standing and for a 200 it takes a table to rest it on.
The technical difference between an instrument for deep and one for the planetary mixer could only lie in the accuracy of the polishing and parabolic of the one for planetary use, where enlargements can be pushed more.
I say “could” why, as I have already argued in some writings, after all, for us amateurs, time is not money, and therefore the creation of a superlative mirror is basically only a matter of time and patience in corrections, and it will still be valid for both the deep and the planetarium.To get an idea of the commitment, calculate that for the realization of my 250F5 (whose realization diary is written in some articles here), starting from a pair of glasses already blanked at the definitive radius of curvature, it took me thirty hours of work.
Certainly also having to carry out the excavation of the initial spheroid by hand, it will take just as long, but in any case, not much is needed to complete the work.
It is said “working one hour a day” to give an idea of the average of a commitment that can last a month without roughing, or two months with the curve roughening, as in the beginning, that is, digging the curve and refining the surface and polishing, there are no time limits; while being corrected (especially towards the end of the work when the margins of tolerance are gradually narrowing), often make corrections that consist of less than 10 minutes of work…and then having to wait the next day (if you don't work with borosilicate glass) to perform the Foucault test and see the results of that correction.
hello Giulio, thanks for the welcome! I have read practically all the articles here on grattavetro and I agree with you that, for us, the pursuit of perfection is almost a duty since we don't cost anything
The glasses they should get me are the records from 600 mm of Suprax which I will then have to cut to size. It won't be as good as Supramax or Duran but I think you can still make some respectable mirrors without fainting… especially at the beginning of my adventure.
I'll have to start from the initial rough, therefore the commitment will be greater, but it is not an open heart surgery… nothing serious can go wrong, badly it goes away! However, I didn't think it was that complicated to find glass!!!Hi Stefano , A beautiful presentation that conveys enthusiasm, passion and creativity therefore, to all effects, you are already a grattavetro, you don't miss anything !Welcome among us
About the glass, I thought that the Suprax had been out of production for several years and for optical-astronomical applications Schott only made Supremax (borosilicato) e Zerodur (ceramic ), but it is possible that I am misinformed…
Hi Massimo, thank you, I'll start to qualify then! Seriously, not finding information about the Suprax on the schott website, I also thought it was no longer produced, so a friend called Schott directly to ask how to find Supramax with relative prices. He was told that Schott only sells to companies in the industry and that he could still have saved money by using Suprax only supplied in discs from 600 mm… But if you tell me that, you strengthen my suspicions…
I have toured a lot of glass factories in my area but everyone talks about thicknesses that do not exceed 19 mm and above all nobody deals with anything other than normal industrial glass. I would like to be able to choose diameter, thickness and quality of the glass but the Supramax and the Zerodur have really high prices. I have seen Supramax blanks since 300 mm thickness below 40mm to more than 400 euro… Without considering that at that point as a tool it would be crazy to use a twin disc
You who use?I am inclined towards normal glass (calcium-soda), and why I expressed it in the article on my acclimatization tests. And also prrchè in thickness 19 mm is suitable for making mirrors up to 300 (but Mirco, if I am not mistaken, made you a 400) , and it is glass available in industrial glassworks. who work for industry and construction (example: production of slabs as walkable glass tops); in practice, as the Ferraris glassworks in Asti describes on its website.
the cost of two discs from 300 chamfered and unpolished cut, I don't think it can differ much from 100 total euros spent by me three years ago.Outside of didactic football, prices are impossible. But a disc would be enough only if a tool made with a steel aqueduct flange was used ( as Mel Bartel described in an article that I could pass on to you if you weren't away from home)., or a plaster tool with embedded stoneware tiles or iron hexagonal nuts (see a specific Gordon Waite movie on youtube).
I had enjoyed reading your article on acclimatization tests and on the fact that a thinner glass, provided it is supported by a well-made cell, it follows better the thermal excursions etc but I thought that a glass of superior quality, when taken in similar thicknesses, was superior in performance. For example a Supramax with thickness 20 mm and a calcium sodium with thickness 19 mm will have differences while maintaining a similar acclimatization curve… but I do not understand and I could say cialtronate.
On Stellafane I saw various techniques for the creation of ceramic tools, metallic and various alternatives but I see the glass tool more convenient for observing the contact points, for example (I know there are so many methods), for testing and more. Clearly, if you go to certain glasses, the use of a twin tool is out of the question, it would border on blasphemy.
A glass factory in the area told me that for industrial glass up to 19 mm has no problem providing it to me, already cut to size. Tomorrow morning if I can take a step to get me a price of two discs. If we are more or less around the figure you suggested, I take out my wallet and greetings.I believe that the glass called Supramax is already from the boron-silicate family, (I seem to remember similar to the bk7, but I could be wrong).
Those glasses , although entry-level of boron-silicates, they certainly have the advantage of a lower expansion coefficient compared to sodium calcium when the temperature changes.
And this has a modest positive aspect in observation, but very large especially during the manufacturing / parabolic process, when the abrasion work would not have dilating thermal effects on the glass, and it is no longer necessary to wait for the time of a stabilization that already exists, to be able to switch to testing, making several corrections instead of just one per day, as an obligation on sodium calcium.The cost of those advantages, however, is disproportionate for the user, but very interesting for industrial production , tantopiù (that like VAT) makes him pay everything to the acquirendte.
I (….but they are of good mouth), I have dobsons with glass mirrors of the two types; but if I don't see the color of the glass, I wouldn't notice the difference just by looking.
Hi Stefano, A warm welcome also from me.
You are about to start a wonderful adventure that will bring you many headaches but also incredible satisfactions. I'm not so experienced that I can give you advice, the only mirror I have worked on so far is a 200mm mirror that I am completing with a multilayer Dobsonian structure and aluminum tubes.
The only thing I feel like telling you is to hold out when difficulties inevitably arise. Eventually you will see the solution is always found.
Good luck
GiuseppeIt is good for me to underline that this blog was born with the specific purpose of EXPLAINING AND HELPING IN GROUP.
EXPLAINS what are the problems encountered in facing the realization of the primary mirror of your telescope, so that everyone can find out if they believe that the commitment is within their reach. Thinking, however, that there is GROUP AID here, who can give advice in the light of his own positive experience already achieved on the subject.We are not “experts” but each of the participants in the Grattavetro knows his own thing by speaking from his own experience, and help others, Because in a group we work better making less mistakes.
Thanks Giuseppe, the challenges are beautiful for that… The obstacle presents itself, we study how to deal with it, you pass it and rejoice… It is not surpassed? Try again.
In the end I opted for a 300mm f / 5. I'm waiting to call the glass factory to tell me the total and then give him the green light or not. I asked for two 305mm discs with 19mm thickness, of non-tempered calcium-sodium glass.
Now then I'll open a separate thread since this is the section for presentations. However, my concept would consist of a Dobsonian with a full aluminum structure, designed with Solidworks and machined with cnc. For the tubes I would like to use carbon. I will think a little’ what to do!
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