The making of 30 inch telescope - 1, arrival of mirror blank

自製天文望遠鏡 牛頓望遠鏡 杜蘇式 卡式 設計和磨鏡方法<br>
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Chanlunlun
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The making of 30 inch telescope - 1, arrival of mirror blank

文章 Chanlunlun » 週四 17 3月, 2005 17:52

Dear ATMs,

It has been the age of great revolution. Aperture fever has just been initiated and can hardly be stopped by anyone.

Following the completion of the 24 inch telescope we immediately start up the 30 inch project. This 30 inch telescope is actually a copy of the 24 inch except that it has a bigger primary, enabling it to have a 56% more light gathering power than a 24 inch telescope.

Unlike the 24 inch the 30 inch telescope is designed so that it will normally be viewed with a bino-viewer coupling with a UHC nebular filter. Two slow motion motors will also be fitted onto the altitude and altzimuth axis so that tracking is possible even in high power.

Rough grinding will be started as soon as possible. The 30 inch mirror will be grinded upon an identical 30 inch tool. We use traditional technique, taking no chances.

With the arrival of the 30 inch mirror blank today we are looking forward for a new start in telescope making history in Hong Kong.

Best regards
Chan Yuk Lun
17-3-2005
附加檔案
30_2.jpg
The 30 inch mirror blank. It is real big, actually it is as big as a table. It requires 4 students to take it to the optical shop for rough grinding.
30_2.jpg (76.61 KiB) 已瀏覽 33316 次

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Wongsir
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文章 Wongsir » 週四 17 3月, 2005 18:16

玉驎兄,

20多年前創造歷史,磨了一枝全港最大的4吋折,前無古人,後無來者;
今天再創高峰,要磨出30吋全港最大に徑望遠鏡. :shock: :shock:
努力,鏡神,我和大家都全心一意支持你.


Wongsir
17-3-2005

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Astrocat
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Re: The making of 30 inch telescope - 1, arrival of mirror b

文章 Astrocat » 週四 17 3月, 2005 18:22

Cool! You're about to break the record again. 8)

May i know where you bought the mirror blank? And, is it a Pyrex or advanced material like Zerodur?
Chanlunlun 寫:Dear ATMs,

It has been the age of great revolution. Aperture fever has just been initiated and can hardly be stopped by anyone.

Following the completion of the 24 inch telescope we immediately start up the 30 inch project. This 30 inch telescope is actually a copy of the 24 inch except that it has a bigger primary, enabling it to have a 56% more light gathering power than a 24 inch telescope.

Unlike the 24 inch the 30 inch telescope is designed so that it will normally be viewed with a bino-viewer coupling with a UHC nebular filter. Two slow motion motors will also be fitted onto the altitude and altzimuth axis so that tracking is possible even in high power.

Rough grinding will be started as soon as possible. The 30 inch mirror will be grinded upon an identical 30 inch tool. We use traditional technique, taking no chances.

With the arrival of the 30 inch mirror blank today we are looking forward for a new start in telescope making history in Hong Kong.

Best regards
Chan Yuk Lun
17-3-2005

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Wah!
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文章 Wah! » 週四 17 3月, 2005 19:46

應該係青玻璃吧?
係一寸厚還是寸半厚呢? :roll: :roll: :roll:

Chanlunlun
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Re: The making of 30 inch telescope - 1, arrival of mirror b

文章 Chanlunlun » 週四 17 3月, 2005 23:12

Astrocat 寫:Cool! You're about to break the record again. 8)

May i know where you bought the mirror blank? And, is it a Pyrex or advanced material like Zerodur?
Dear Mr. Astrocat,

The mirror blank was bought at a glass shop next to our school. The blanks of our 14 inch, 10 inch ands 24 inch telescope were all bought at the same shop. they sold quality glass at a very reasonable price.

The glass is ordinary float glass, which happens to be the most homogenious type of glass available in the world. We have bought two disks, one for the mirror and one for the tool. Both of them are 30 inches diameter.

The thickness of the each blanks is 1 inch.

At such size both Pyrex and Zerodur are extremely expensive. I'm afraid that very few peopel could afford to buy them.

Best regards
Chan Yuk Lun

Chanlunlun
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文章 Chanlunlun » 週四 17 3月, 2005 23:15

Wongsir 寫:玉驎兄,

20多年前創造歷史,磨了一枝全港最大的4吋折,前無古人,後無來者;
今天再創高峰,要磨出30吋全港最大に徑望遠鏡. :shock: :shock:
努力,鏡神,我和大家都全心一意支持你.


Wongsir
17-3-2005
Dear WongSir,

Thanks for your supporting.

How about your 40 inch telescope project ? I'm looking forward to be at your service.

Best regards
Chan Yuk Lun

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Wah!
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Re: The making of 30 inch telescope - 1, arrival of mirror b

文章 Wah! » 週四 17 3月, 2005 23:15

Chanlunlun 寫: The glass is ordinary float glass, which happens to be the most homogenious type of glass available in the world.
Are you sure?! :? :?
How can you be so sure? Any evidence??? :? :? :? :? :?

Chanlunlun
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文章 Chanlunlun » 週四 17 3月, 2005 23:17

Wah! 寫:應該係青玻璃吧?
係一寸厚還是寸半厚呢? :roll: :roll: :roll:
Dear Mr. Wah!

It's a one inch thick float glass blank.

I've heard that there exists float glass of thickness 1.25 inch but I never find them.

Best regards
Chan Yuk Lun

Chanlunlun
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Re: The making of 30 inch telescope - 1, arrival of mirror b

文章 Chanlunlun » 週四 17 3月, 2005 23:26

Wah! 寫:
Chanlunlun 寫: The glass is ordinary float glass, which happens to be the most homogenious type of glass available in the world.
Are you sure?! :? :?
How can you be so sure? Any evidence??? :? :? :? :? :?
Dear Mr. Wah!,

Yes I'm sure. Float glass is the most demanding glass in the world ( even more demanding than optical glass !!) because it's used in building skyscrapers. Any stress, any inhomogenity, especially these glass always appear one piece in big area, will cause glass wreckage which is very dangerous.

The method employed in manufacturing of these glass ( floatation method inside inert gas chamber - that's why such glass is called floart glass ) guranteed that such glass will have zero stress and be very homogenious.

Otherwise why do you think that we can make such a large astronomical mirror out of float glass ? We will never figure the mirror down to the required paraboloid if the glass itself is not homogenious and stress free enough.

Best regards
Chan Yuk Lun

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Wah!
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文章 Wah! » 週四 17 3月, 2005 23:36

I don't think scientists will give stress to their glass and let their glass not homogenious.
That's why I doubt you use "in the world".

Of course I don't have evidence or figures, but I still believe that optical glass could be better.

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Astrocat
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文章 Astrocat » 週四 17 3月, 2005 23:41

Chan sir, it sounds really great.

But, do you think 1" think is sufficient for making 30" mirror? What's the planned focal ratio? How's the finite element analysis?

I absolutely believe you've taken all these into considerations, however, any sharing and enlightenment for us?
Chanlunlun 寫:
Wah! 寫:應該係青玻璃吧?
係一寸厚還是寸半厚呢? :roll: :roll: :roll:
Dear Mr. Wah!

It's a one inch thick float glass blank.

I've heard that there exists float glass of thickness 1.25 inch but I never find them.

Best regards
Chan Yuk Lun

Chanlunlun
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文章 Chanlunlun » 週五 18 3月, 2005 00:16

Astrocat 寫:Chan sir, it sounds really great.

But, do you think 1" think is sufficient for making 30" mirror? What's the planned focal ratio? How's the finite element analysis?

I absolutely believe you've taken all these into considerations, however, any sharing and enlightenment for us?
Dear Mr. Astrocat,

The mirror cell is of 27 points floatation type. Finite elemnet analysis shows that under such supporting the mirror will have a mximum sagging of about 1/8 wave PV - just sufficient for astronomical purpose.

The telescoep will have a f/ratio of f/3.3, using intruding focusng method to reduce th esecindary to a 4 inch minor axis so as to save money and weight.

My sharing is that to make big telescope make good plan. Do according to planning. Keep timing as accurate as possible. You may work earlier than schedule but never left behind by schedule. Never let delay happens - you make one day delay, soon you will find that you make one week delay and soon you will find that you make an eternal delay. I've seen a lot, especially in telescope making.

Most of all book keeping all cash flow to avoid over budget. We built the 24 inch out of HKD4000 only. We can build the 30 inch using even less money, provided that we spend on a knife edge.

Best regards
Chan Yuk Lun

Occultation
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註冊時間: 週六 05 6月, 2004 13:42

Re: The making of 30 inch telescope - 1, arrival of mirror b

文章 Occultation » 週五 18 3月, 2005 06:09

Dear Y. L. Chan,

90% of flat glass in the world is manufactured by float glass method, The raw materials (silica sand, calcium, oxide, soda and magnesium) are properly weighted and mixed and then introduced into a furnace where they are melted at 1500° C. The molten glass then flows from the glass furnace into a bath of molten tin in a continuous ribbon. The glass, which is highly viscous, and the tin, which is very fluid, do not mix and the contact surface between these two materials is perfectly flat.

From the experience of working in a laboratory with glass safety testing as well as visiting the float glass manufacturing factory (China and oversea) and exchange experience with them. Float glass is NOT stress free and NOT that uniform as you think. Meeting the construction standard on glass safety doesn't mean it is optically flat, totally free of stress and defect. I don't know how important and to what extend is stress free and homogeneous required in the mirror making process especially a big one you mentioned here. May be you can tell us more on this.

One thing I do agree with you is ordinary float glass is cheaper than high quality optical glass



Chanlunlun 寫:
Wah! 寫:
Chanlunlun 寫: The glass is ordinary float glass, which happens to be the most homogenious type of glass available in the world.
Are you sure?! :? :?
How can you be so sure? Any evidence??? :? :? :? :? :?
Dear Mr. Wah!,

Yes I'm sure. Float glass is the most demanding glass in the world ( even more demanding than optical glass !!) because it's used in building skyscrapers. Any stress, any inhomogenity, especially these glass always appear one piece in big area, will cause glass wreckage which is very dangerous.

The method employed in manufacturing of these glass ( floatation method inside inert gas chamber - that's why such glass is called floart glass ) guranteed that such glass will have zero stress and be very homogenious.

Otherwise why do you think that we can make such a large astronomical mirror out of float glass ? We will never figure the mirror down to the required paraboloid if the glass itself is not homogenious and stress free enough.

Best regards
Chan Yuk Lun

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Wah!
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文章 Wah! » 週五 18 3月, 2005 09:33

This is the best picture I can find from the web.

圖檔

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XR250
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文章 XR250 » 週五 18 3月, 2005 10:12

Chanlunlun 寫:
Astrocat 寫:Chan sir, it sounds really great.

But, do you think 1" think is sufficient for making 30" mirror? What's the planned focal ratio? How's the finite element analysis?

I absolutely believe you've taken all these into considerations, however, any sharing and enlightenment for us?
Dear Mr. Astrocat,

The mirror cell is of 27 points floatation type. Finite elemnet analysis shows that under such supporting the mirror will have a mximum sagging of about 1/8 wave PV - just sufficient for astronomical purpose.

The telescoep will have a f/ratio of f/3.3, using intruding focusng method to reduce th esecindary to a 4 inch minor axis so as to save money and weight.

My sharing is that to make big telescope make good plan. Do according to planning. Keep timing as accurate as possible. You may work earlier than schedule but never left behind by schedule. Never let delay happens - you make one day delay, soon you will find that you make one week delay and soon you will find that you make an eternal delay. I've seen a lot, especially in telescope making.

Most of all book keeping all cash flow to avoid over budget. We built the 24 inch out of HKD4000 only. We can build the 30 inch using even less money, provided that we spend on a knife edge.

Best regards
Chan Yuk Lun
Beside money and schedule, do you have any contingency plan for the 1" glass?
Can you share your plan with us?

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