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Topics - Ricky Mondal

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Just a question that came to me. Thanks for any answers!

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hello, have been reading from cloudynights and this is my first post here.

currently I am planning on a 40", or 1m f/3.3 Dob, with a glass supplier who can manufacture fused silica blank for me. I will try to grind and polish myself, and may need assistance from third party on final figuring.

the question is about the mirror blank. Yes, I notice some famous optical shops are making mirrors of this size, with thickness 50, or 60+ mm only, but I am not sure if I can be such skillful to handle such thin blank without astigmatism. Going up to 80 or 100mm thickness will be much safer for me, but the weight will go up to 150-180Kg range, which is too much for me to handle. I want to keep the blank weight at 100-120Kg range (of course lighter is better, but I don't want to risk the optical quality, or raise the challenge of polishing too much). So any suggestion what thickness I should choose?

the other approach will be machining the blank to remove some weight, and manufacturer can do that for me at certain cost, and re-anneal the blank for 72hrs to remove residual stress (is that enough?).

without any evaluation on FEA (I have no experience on that, except Plop), I just casually draw two examples as below, one is drilling a number of holes evenly distributed over the surface but keeping a distance from the edge, say 50mm. The other is rounded corner triangle, of course both approaches must be designed and evaluated with the mirror support say 18 or 27 floating points support by FEA. I think Removing 30-40% of the weight will attain the goal above.... any available software can do such evaluation?

One thing to add, the telescope is for stationary use, but keeping the weight lower will make a lot of grinding and polishing work, mounting and maintenance work easier. Temperature stabilization is a merit, though in our place the night temperature is quite stable.

thank you for your advice here.Attached Thumbnails


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Beginners Forum / looking for a bit more help regarding equipment
« on: December 31, 2017, 03:54:46 AM »
My name is David, and I'm a 9th grader looking to get in Astronomy, although it is kind of hard here in India. I've saved up 45 thousand, and my father is willing to pay a bit as well. My total budget is therefore 55k INR. I have posted earlier in this forum, and with your help I have decided on the Celestron C6 sct OTA, which my uncle will bring from America. This will set me back around 25k, so I still have 30k, but I am unsure of what exactly to spend it on..
http://www.highpoint...etail-91010-xlt

1) The mount: This is obviously really important, so I think I should spend around 20k here.
I may get a Bresser Exos 1, I can buy it in India and that is convenient
http://www.tejraj.com/exos1.html

This alt az mount by GSO was also recommended, and it looks easier to use than the Exos 1, but I may look into AP later, so I'm unsure here..
http://www.tejraj.co...ith-tripod.html

The mount I think is best is the Bresser Exos 2, which is available in the USA for about 350 dollars (20k approx) and if my uncle can bring this, I think I will go for this one.
https://www.bhphotov...equatorial.html
https://explorescien...exos-2-eq-mount

All the mounts cost around 20k, so that leaves 10k for eyepieces and such. The OTA comes with a 25mm eyepiece.

2) Eyepieces: I think this is where I am having the most trouble.. I was originally going for a kit, but decided on buying individually. Are there any filters I should get? How about barlows? What sizes do I need? I am leaning towards DSOs and visual but if possible I would like to do AP in the future.
These are cheap, but what the heck, might as well consider them..
http://www.tejraj.co...eces-astro.html

I am actually think about either of these series though.
http://www.tejraj.co...uperplossl.html
http://www.tejraj.co...-superview.html

Also thought this seemed pretty cool.
http://www.tejraj.co...ieces-zoom.html

Some other names I've heard are Celestron Ultima andBaader Eudiascopic
https://www.astronom...pieces_c60.aspx
http://www.astroshop...yepiece/p,10726

3) Just wondering if I need any accessories, such as eyepiece box or dew shield. Perhaps a dessicating cap? I live in the tropics, so that might be useful. Maybe a different finderscope? I really don't know, I need some help here as well..

Thanks,

David

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Public beta release with full support for CP4 and IP connections directly to the CP4.http://www.astro-phy...pcc-release.pdf

http://www.astro-phy...c/apcc-download

You will need the updated AP ASCOM driver too.

http://www.gralak.com/apdriver/

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Light Pollution Topics / Pope Benedict XVI; Light Pollution linked to Evil
« on: December 26, 2017, 11:40:58 PM »
From parts of an interesting story by the Blade News Service, 4/8/2012:"Pope beckons faithful to return darkness. ''``Benedict voices fear that evil is triumphing":Vatican City -- Referring to urban surroundings; throughout the Easter Vigil, Saturday night, Pope Benedict XVI expressed his concern about protecting the environment was quoted as stating, "Today we can illuminate our towns so brightly that the stars in the sky are no longer observable.   Is this not a picture of the problems brought on by our version of enlightenment?"

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About the evenings of August 26-28 (27, 28, and 29 UT) I did some observing with a singlet (best guess) refractor.  The 42mm f/14 instrument was stopped down to 12.7mm (1/2 inch) f/47 for the majority of the observations.  I built a 'brand new' OTA round the sole real components (intention in cell/dew-shield) out of what appeared at first to be an entirely useless telescope.

A 32mm Plossl eyepiece supplied a magnification of nearly 19x using a true area of 3 degrees for many observations.

The moon at 12.7millimeter f/47: On the first evening 33 craters were sketched, 17more were added on the 2nd night and 20 more on the next.  A total of 70 different craters were sketched.  A couple of even sported visible central peaks.  The 1/2-inch scope supplied a fresh, sharp image that was pretty much free of chromatic aberrations.  Also sketched ware maria: Frigoris, Serenitatis, Crisium, Tranquillitatis, Fecunditatis, and Nectaris in Addition to Sinus Asperitatis.

At full aperture (42mm f/14) the moon was quite vibrant -- so much that it resulted in terribly fuzzy lunar detail.  Significantly more detail was visible once the telescope was stopped down to 1/2-inch!

In the 12.7millimeter aperture Saturn consisted of a small disk inside a little dimmer ellipse.  Sometimes Saturn looked like a single, central disc using a bigger, less bright disk in near proximity to both sides -- similar to one of Galileo's Saturn sketches.

Vega at 12.7mm consisted of a nice, sharp, airy disc along with one relatively faint diffraction ring.

In a 42mm aperture Vega was interesting.  It consisted of a yellow '+' sign using three orange-red-crimson rays/spikes radiating upward and three further downward.  Three, more tightly spaced, greenish rays/spikes radiated out into the left and right.

Back to some 12.7millimeter aperture for deep-sky and double stars: M13, M92, M31, M32, M33, M57, and M81 were detected.  Mizar and Abireo were spit, though their companies were not too bright.  Epsilon Lyra was a wide, simple double.  The Perseus Double Cluster appeared to be missing many of its celebrities.

Changing to complete (42mm) aperture changed the telescope into a really competent deep-sky instrument.  M110, M101, and M82 became easily visible (bear in mind, my skies was not entirely free of smoke from fires near and far.)  M81 and M82 were at their lowest point in my skies -- between Polaris and also my north west horizon.  A number of M45's stars exhibited chromatic artifacts in the kind of rust-colored spikes.  The double bunch sprung back into life.

I was most amazed by M31-32-110 at the 42mm aperture.  M31 stretched across the majority of the three degree area.  M110 was easily visible as the elliptical glow I had grown used to in other instruments.  The three together were so amazing and easily visible that it was easy to picture I had been using a significantly larger and high quality telescope.  Certainly, many DSOs are within reach of the complete 42mm aperture.

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