Building a Cassegrain

[geminimac]

hello Henry,

thanks for the answers…
but not being Pyrex brings problems to the project success?
There are pros about it?

The guy e-bay is just in Cremona…I know that is your same supplier

cmq crepi the wolf

[EnricoR]

There are no real contraindications, the substantial difference between the two panes is that the pyrex has lower coefficient of thermal expansion compared to normal calcium sodium (ie, it deforms less by changing the temperature with respect to calcium sodium) but here we enter a specific field where the other guys you definitely will explain better than I (I remember reading something about that in a post Giulio…but I have forgotten it)

[Massimo Marconi]

I agree with Henry, and I think that for practical purposes there is little else to say, Oh well… Julius and Mirco could write a treatise on this subject, but I will summarize in two words: If on equal terms (support, by boundary layer extraction systems, temperature difference with the environment, etc… ) the titled pyrex goes into temperature e.g.. in 20 minutes, the “poor” astronomer with vetraccio those will have to wait ten to fifteen minutes longer , after which you may enjoy the wonders of the sky without any difference compared to connect with low expansion borosilicate.

Is’ Clearly, in those twenty minutes even on pyrex mirror you will see a ciofeche.

[geminimac]

Ok so in my opinion it is not a problem to worry about….so much 10 so much 15 min at the end temperature when it is in his work place him well…I was interested to know this!
Once this telescope I expect great satisfaction
Enrico from your post I read that you're in Carpi….We are close enough to me that I'm in Modena…I just wanted to know if you can advise me who's performing aluminum coating on the glass…I have not found a single one

Thanks for the clarification guys!

[Lelio]

hello Gemini, I'm in the province of Varese and I go to Milan from zaot, for you should be comfortable Zen. Try to find an observatory with the vacuum chamber in your area are competitively priced.

[geminimac]

hello Lelio!

I will try definitely!!

Thank you

[EnricoR]

hi Luca, I had come to doubt you were from around here when I read that you could retrieve tiles from the workplace ...

As for the 'aluminizing, the research that I did on-line at the time, It turned out to be nothing in the area here, the only remain Zen (Venezia) e Zaot(Milano).

Good idea, I had no way considered, Lelio to try ... ..

[Lelio]

Many years ago I met a good grattavetro Imola and he was alluminare from an observatory in Bologna, then I did not delve because for me it was convenient zaot, I do not even know what would be, I know that makes some Asiago mirror.

[Giulio TiberinI]

I live in the province of Asti and My reasons for urgency and safety , arising both from my desire to have in hand as soon as possible the fruit of my work , and also not to risk to entrust it to a courier who perhaps having a fight with his girlfriend, or for other reasons having “bischero dipped in pepper” as they say in Florence, or to “do not put my butt in other people's footsteps” as they say in Trento, avoiding that the guy I did “to fly” his truck packaging, albeit in a wooden box , I always preferred to bring the person to alluminare my mirrors and I came back to take them back in a few days away.

To go to ZAOT which is located in Vittuone (just west of Rho in Milan) I though I only 170km of highway that are 3 hours round trip; However, less than the distance with my best sky observations, it is now only by SQM 21,5 /6 Chiappera (CN).

From Carpi to Vittuone km perhaps there are only 40 more, and they are more or less equivalent to those that would lead to venice. Then there is the advantage of the choice based on the best price

[geminimac]

In fact it is to assess both the aluminizing price shipping(risky says Giulio) or away from face…

Now we will see when the opportunity arises

Anyway thanks for the info!

[geminimac]

update a little post…

these days I reached the beauty of 4,6 mm arrow…now you start to see some results

[Massimo Marconi]

Well ! the work progresses
Forgive me, but I have not yet figured out what you decided to do the mirror : F4, F3 or … ?

[geminimac]

I finally settled on a F3
I want to complete the initial project even if it means to deal with a very difficult to achieve secondary convex and therefore much more time to lose
It may seem strange but the hardest things fascinate me….it's stronger than me!

[Lelio]

First mirror? First time you compare yourself with a shorter focal length? Have a listen to those who did some normal newton mirror and normal mean F6 or higher, do a great newton F3.5 / 3.8 already difficult to achieve if not difficult for the vast majority of grattavetro. Of course if you settle the minimum wage with respect to lambda, coma, and especially always astigmatism that there is no edge retorted or other processing disadvantages that weaken virtually all cravings to excel in almost all on the short focal lengths can then go but not expedient, you will not have a great mirror.
I do not want the teacher, I am only realistic. You want a mirror excelled in a configuration in which very few compete? Without at least one question, because there are so few who do,?
Why is not convenient, or because it is a quite difficult challenge even for the most experienced?
To give you an example on my way to see, childbirth in fourth on large diameter mirrors, F4 or so but already I think twice under the f4. I would like to do for years in the house the plane mirrors, I'm not even approached us after reading some articles. I wonder if maybe I will need a 100 or I try to do well, but already I know I will be a challenge given that the sacred cows of grattavetro have had several failures.
Returning to the optical configuration, but you want to make the brightness of a newton little obstructed than any other type? Would introduce an additional advantage, the contrast on a craft mirror devoid of surface roughness gives you spectacular images. Also for me as a visualist the Cassegrain are dark, dark , unexciting Gray, of ciofeghe only useful for planetary and photographers, with a ridiculous useful field.
Make a newton F3.5 muster a coma corrector and enjoy like a hedgehog for life!!!!!!

[Lelio]

I see now what you want to do, a system 5 mirrors? 88% reflectivity mirror every thing you eat in terms of reducing brightness? I do not know calculate it but 10% lost for every mirror ago 50% thrown away, why throw it? Obstruction around 40% the Cassegrain and your efforts to build it are useless, bought a pair of binoculars and you are set
There are the newton photo looks the Alluna Optics site, Northek etc. cost a kidney!!! and those projects make sense!

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