The 24 inch mirror - WORK COMPLETED

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>
佛科試鏡法 佛科刀片儀 光柵試鏡法 光柵片
Chanlunlun
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註冊時間: 週四 09 10月, 2003 21:06

The 24 inch mirror - WORK COMPLETED

文章 Chanlunlun » 週二 06 4月, 2004 13:10

Dear ATMs,

Finally it is accomplished.

On the day of 3rd April 15:38 hrs it marked the completion of the parabolization of the 24 inch mirror. After the last 9 minutes of final strokes by the 8.5 inch lap for reducing a small plateau in the mirror center, ( yes, only 9 minutes, you can imagine how small the amount of glass, most probably not more than 1/4 of a wavelength, had been removed in this very 9 minutes ) the huge glass disk was again transported to the mirror stand for another round of testing. It had been 24 working hours since parabolization first began.

After some complicated alignment, which already became routine procedures, the image of the slit was located alongside the knife edge. With the eye situated right at the image of slit the whole mirror was visually illuminated, just like looking at sunset on the horizon, with the exception that the intensity was much weaker. Cautiously with alert, the knife edge was slowly cut into the image of the slit and….., all of a sudden, the already evenly illuminated mirror surface darkened all at once under the Offner null tester. It had only one implication – the mirror surface had already reached a perfect parabola.

So the war was over, at 4:00 p.m., on the date of 3rd of April 2004.

By completion of this 24 inch mirror we have broken several records in Hong Kong which include

1. It is the biggest mirror ever home made.
2. At an edge thickness of 25 mm, it is the thinnest mirror of this size ever made.
3. At a weight of only 28 lbs, it is the lightest mirror of this size ever made.
4. At a cost less than HK$ 2500, it is the cheapest mirror of this size ever made.
5. It is the first mirror tested by the Offner null method.
6. At a total weight of no more than 65 lbs, it will be the lightest 24 inch telescope.
7. At a construction cost of no more than HK$4500, it will be the cheapest 24 inch telescope.
8. At a f/ratio of 3.4, it will be the fastest 24 inch telescope.

The mechanical construction work including the 18 point mirror floatation cells, the struss tube body and rocker arms …...etc will be commenced promptly. So far we have spent around HK$2400, there is not much money to be spent any further except for the diagonal mirror which costs HK$1400 and a focuser which cost another HK$200. ( A ZhiTong focuser will do a good job ). So we have a very good hope of not exceeding the HK$ 4500 budget for completion of the whole project.

Finally I would like to take this opportunity to express my gratitude towards Wong Sir who had made available of his lathe for fabricating the Offner null tester. I also thanks for the members of the mirror making team who have been spending so much efforts in pushing the huge glass disks, without them the mirror will not have been finished so early.

So far so good. We wish for the early completion of the entire 24 inch telescope.

Best regards

Chan Yuk Lun
5-4-2004
附加檔案
profile_2004.4.5a.jpg
The Ronchigram under the Offner null tester. The straight bands indicates a null figure, which implies that the mirror surface is a good parabola.
profile_2004.4.5a.jpg (19.77 KiB) 已瀏覽 149830 次
mirror_lap.jpg
The 8.5 inch parabolization lap and the 3.5 inch figuring lap for parabolizing the mirror.
mirror_lap.jpg (73.88 KiB) 已瀏覽 149826 次
completed_mirror.jpg
The finished 24 inch parabolic mirror, deeply curved yet crystal clear, waiting to be star tested.
completed_mirror.jpg (44.37 KiB) 已瀏覽 149826 次

CK
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文章: 467
註冊時間: 週六 28 6月, 2003 14:22

文章 CK » 週二 06 4月, 2004 13:20

恭喜鏡神,不但成為香港自製望遠鏡最大的紀錄,更是成功製作 F/3.4大主鏡的第一人!! :shock: :shock:

ck

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豆豸苗
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文章 豆豸苗 » 週二 06 4月, 2004 13:38

嘩. 恭喜呀~~ \(^o^)/

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Cindy
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文章 Cindy » 週二 06 4月, 2004 13:41

嘩!嘩!嘩!!!!

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Wongsir
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文章 Wongsir » 週二 06 4月, 2004 15:22

恭喜!!

:D :) :o :lol: :P :mrgreen:


Wongsir
6-4-2004

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Wah!
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文章 Wah! » 週二 06 4月, 2004 15:31

:shock: :shock: :shock:

bandofbrother
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文章 bandofbrother » 週二 06 4月, 2004 15:41

好勁ar
恭喜曬!!!!!!!!

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天屍仔
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文章: 65
註冊時間: 週六 12 7月, 2003 20:14

文章 天屍仔 » 週二 06 4月, 2004 19:46

陳Sir恭喜哂!

其實你會點評價個鏡面by looking at the offner null image? I mean how perfect it is?

Anyway, I feel so excited, pls remember to call me, I would really like to take part in it! Really hope the AL exam would pass quickly...

Ma Ka Hei

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Wah!
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文章 Wah! » 週二 06 4月, 2004 22:42

期待star test~
究竟參與磨鏡的同學名單有幾多人呢?

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david_kmng
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文章 david_kmng » 週二 06 4月, 2004 22:47

恭喜!

Hope I can start my 20" project :)

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Subaru
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文章 Subaru » 週二 06 4月, 2004 22:58

到時可否join埋用支24"睇deepsky?

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扒飯撈麵
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文章 扒飯撈麵 » 週二 06 4月, 2004 22:59

恭喜曬
wah!
你的12.5要加倍努力喇

Chanlunlun
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文章 Chanlunlun » 週二 06 4月, 2004 23:07

天屍仔 寫:陳Sir恭喜哂!

其實你會點評價個鏡面by looking at the offner null image? I mean how perfect it is?

Ma Ka Hei
Dear Mr. Ma,

Theorectically a calibrated Offner null tester could test a parabola down to 1/50 wave P.V. However ours are not calibrated and hence there is why we need a star test, just to make sure.

It is extremely difficult to calibrate an Offner null tester, even NASA miscalibrate it ( remember how the primary mirror of Hubble Spcae Telescope suffered ...... ).

Since you have asked, I tell you a little secret - personally I have already calibrate our Offner tester by looking striaght into the 24 inch mirror focusing at a distant lamp, using a Or 12.5 mm eyepiece giving about 170X. The mirror showes very liitle undercorrection although the Offner showed a null. I recalculated everything in my computer and make another simulation and readjust the Offner accordingly. I refigure the mirror again such that it again showed a null in the adjusted Offner tester. This time the distant lamp shows no sign of under ro overcorrection.

If the mirror is not a perfect parabola, it is very close to it.

Best regrads

Chan Yuk Lun

Chanlunlun
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文章 Chanlunlun » 週二 06 4月, 2004 23:13

Subaru 寫:到時可否join埋用支24"睇deepsky?
Dear Mr. Subaru,

You are always welcomed.

Best regards

Chan Yuk Lun

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daniel cck
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文章 daniel cck » 週三 07 4月, 2004 00:19

恭喜!

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