蘇魯定先生的鏡-1

檢測望遠鏡光學部份,赤道儀機械組件,目鏡配件和拍攝器材 CCD等...
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Chanlunlun
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文章: 3833
註冊時間: 週四 09 10月, 2003 21:06

蘇魯定先生的鏡-1

文章 Chanlunlun » 週四 21 6月, 2007 16:29

Dear Mr. So,

In the first place I would like to beg for your forgiveness for my late response. Your mirror had arrived Hong Kong early this year and WongSir demanded that the mirror must be handled with great care, avoiding upsetting your great support.

You had mentioned about using the auto-collimation test for figuring this mirror. This test is well-known for its extreme precision and a mirror, under such superb test, could easily reach an error not exceeding 1/20 wave P.V. I firmly believed that what I could do was just to reconfirm your result.

Due to the lack of a sizeable standard optical flat, I decided to test the mirror by the elementary Foucalt knife-edge test. Though primitive the method was, great precautions were engaged in order to minimize the errors as mush as possible. These included the use of a big laboratory with all its windows closed aiming to stabilize its environmental temperature. All data were sampled only after a long wait until not a single trace of air turbulence was observed over the mirror. Finally all single data was an average of three samples to make sure for reliable results. Nevertheless the results obtained was quite departed from yours, even under numerous tests, day after day, experiment after experiment. Basically the profile of your mirror is as follows :-

1. There is a shallow “depression”, diameter 4 to 5 cm , lying at center of the mirror. This is by no means surprising since the central portion of the mirror was blocked during the auto-collimation test. There was just was no way to tell how good or how bad the mirror was at this region.

2. Ignoring central portion, the mirror is basically a good paraboloid,. However test after test the results obtained only indicated a 1/6 to 1/8 wave P.V. accuracy. A 1/20 wave P.V. result was never achieved no matter how many times the experiment was carried out.

I belief that I am the one who brought about all these troubles. It is a well known fact that the Foucalt test could accomplish good precision only when the mirror under test is of sufficient long focal length. For fast mirrors, upon knife edge cutting, shadow transient was too quick for average human eye to capture equal grayness accurately. Moreover observer’s subjective judgement also leads to rapid growth of random errors. Mr. So’s mirror is a f/5. With such short focal length together with my poor eyesight it was not surprising that the test was not at all carried out competently.

Now we have a situation here which would, regretfully, lead to the disappointment of both Mr. So and WongSir. In order to fulfill my mission I made my decisive move to make another mirror with accuracy also of 1/20 wave P.V. and hopefully this reference mirror could be AB tested against Mr.So’s, giving a more sounding result. To me who equips with only mediocre ATMing technique the making of a mirror of such precision means a colossal job taking great length of time. It is not until recently that the reference mirror has been finished and with an error envelop of, despite my greatest effort spent, not better than 1/16 wave P.V. It deems that I am a worse ATMer comparing with Mr. So.

To truly fabricate an AB test we need to take care of a lot of recourses – such as two mirror testing rigs, two equatorial mounts and two pieces of identical diagonal flats from the same factory with equal dimensions. The list could be exhausting and preparation job is still not fully ready at the moment. However the individual star test of each mirror has been carried out. Under a magnification of 500X both mirrors performed very nearly identical. If we have to make the preliminary judgement between them all we can say at the moment is that the reference mirror gave a little more sharper and detailed image while the contrast of Mr. So’s mirror was a bit higher. Nevertheless during these two independent observations atmospheric turbulence were not exactly the same and the result was believed to be far from final. At the moment we are still waiting for arrival of all required equipment and hopefully we will come to a decisive conclusion shortly.


Nowadays commercially available astronomical telescopes selling at low prices are pouring into the market and consequently ATMing is a declining hobby both in its quantity and quality. ATMers with superb technique is rarely seen and Mr. So is definitely one of those. I am being inspired, and honored, to have a chance to see your excellent mirror and it is my hope that we will still enjoy the luck to have your continual offering of opinion to improve our ATMing technique.

Looking forward to receive your response, if my humble message worth your notice.

Yours truly,

Chan Yuk Lun
20th June 2007.

( Chinese translated version are following in the same thread)
附加檔案
5.jpg
Mr. So’s mirror under shop test.
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4.jpg
Mr. So ‘s mirror on the test rig, ready for star test.
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3.jpg
The reference mirror (right) and Mr. So mirror (left) and the Couder screen for paraboloid measurement.( bottom )
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2.jpg
The Foucalt test profile of the reference mirror. It has a P.V. error of about 1/16 wave.
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1.jpg
The Foucalt test profile of Mr. So’s mirror. It has a P.V. error of about 1/7 wave.
1.jpg (91.02 KiB) 已瀏覽 24907 次

Chanlunlun
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文章: 3833
註冊時間: 週四 09 10月, 2003 21:06

文章 Chanlunlun » 週四 21 6月, 2007 16:31

致蘇魯定先生:

蘇先生寄來之鏡早於年初收妥,黄隆先生囑咐吾人務必認真處理,免負蘇先生心意。今得蘇先生親製精品,誠惶誠恐, 測試結果, 恐有錯漏,未敢及早公佈,還請見諒。

憶蘇先生所述,此鏡乃出自準直法(Auto-collimation Test)修琢而成,查此法精度甚高,鏡面誤差輕易者不過1/20 波長P.V. 。吾人再度測試,力之所及,不外重新肯定蘇先生之結果矣。

由於吾等缺乏大型標準平面鏡,故衹能使用簡單之佛科試鏡法 (Foucalt Test) 。雖曰土法上馬,然亦沿用嚴謹態度處之。一曰使用倘大之實驗室,並緊閉所有窗户以靜其氣流,數據盡皆靜侍直至氣流擾動低至不能察覺之時才正式取樣。再者每數據皆經三次取樣,索其平均,以達最可靠之結果。然而經多番測試,甚至於不同日子進行同一試驗,結果仍無法與蘇先生所述相符。基本上鏡面呈現如下特性:

1. 於中心處直徑約4-5cm乃一下陷之凹宂。此不足怪,蓋於自準直測試中,鏡面中心為不可見者,此部精確度自然無法控制。

2. 略去上述部份不談,拋物面形狀確屬良好。然而多番測試,得出精確度約為1/6-1/8波長P.V., 奈何無法得出1/20波長P.V.之結論。

結果分歧,錯在我方。眾所周知,佛科刀口儀之於短焦鏡面,刀片入切,其光暗變化甚速。平凡眼睛實難以精細判讀,再計及主觀因素,逐令隨機誤差 (Random Error)急劇上揚。蘇生之鏡焦比為5,焦距頗短,加上本人老眼昏花,自然力有不逮。

事到如今,如何是好?一則有負蘇先生心意,再者亦失黄隆先生所望,此實非吾之所願也。乃痛下決心,亦自行磨製一鏡,精確度亦達1/20波長P.V.者,以為參考之用,盼與蘇先生之鏡作AB比較,結論理應可靠。

惜吾人技藝粗疏,製作此等高水準鏡面,曠時日久,直至最近,參照鏡才得以完成。吾人竭盡所能,鏡面精確度亦不過1/16波長P.V.矣,水平所限,難望蘇先生之項背,亦莫見笑。

嚴謹之AB比較,耗費頗大資源,二台之赤道儀,二副之主鏡台架,二塊同廠同批號同尺寸之对角副鏡,必在同倍同時同目標下交互觀察,凡此種種,頗費周章,一時間未能配合。然二鏡於不同時間之獨立觀察,業已完成。初步觀之,於500高倍之下,二鏡表現,極其接近。強分其差異者,一曰參照鏡像質稍稍幼細結實,一曰蘇先生之鏡反差稍高,可謂各擅勝場。有鑑此等測試非同時進行,大氣穩定度亦不盡相同,一時未可論盡。還盼早日集齊所有資源,進行真正AB評鑑,以證真章。

綜觀全球,廉價之天文鏡大量湧現,ATMer數量江河日下,盛況不再,而當中技術超群者,更如鳳毛麟角,蘇先生肯定為其中之一也。今得睹蘇先生所贈神物,大開眼界,獲益匪淺。吾人技藝粗疏,還望蘇先生日後不吝賜教,以補不足,則吾人幸甚也。

班門弄斧,草草成章,蘇先生亦請見諒。

此致

陳王麟 謹識
2007年6月20日

苏鲁锭
主序星
文章: 280
註冊時間: 週六 19 8月, 2006 21:34

文章 苏鲁锭 » 週五 22 6月, 2007 20:59

陳王麟先生:辛苦您了!谢谢!
毫不谦虚的说,我从您那里学到了很多知识。
这是个失败的镜子。现在总结出来,失败在检测。检测中存在三个问题,
1)用平面镜检测抛物面中心有30MM是检测不出的。
2)抛物面中心“一次”反射刀口仪灯光,抛物面其它部分是3次反射刀口仪灯光,这部分特别亮,影响对抛物面中心附近的仔细检测。
3)刀口仪检测镜子要将镜子翻转检测,这个镜子没有做。
现在2,3问题解决了。镜子的精度还可以进一步提高。
您的检测和我的检测各有所长,从您的检测中反思我的检测,能发现我存在的不足,提高我的检测。
再次谢谢您!
谢谢!!

昆仑
超新星
文章: 1
註冊時間: 週六 02 6月, 2007 15:41

文章 昆仑 » 週日 24 6月, 2007 07:54

今有幸一ç￾¹ä¸¤ä½￾大师的æ￾°ä½œï¼Œå®žåœ¨æ˜¯é«˜ï¼Žé™ˆå…ˆç”Ÿå￾¯å￾¦å°†ä¸¤é•œæ‹￾摄的星点图放到网上,让众多天文爱好者学习欣èµ￾.谢谢ï¼￾

BJDF
主序星
文章: 143
註冊時間: 週日 26 2月, 2006 10:52
來自: 北京

文章 BJDF » 週日 24 6月, 2007 09:21

看陈先生写国文也是很有趣 :lol:
这几遍测试应该是可以的了,只是测试软件还搞不懂,不过从刀口仪阴影判断我不用分区盖板,只用记号笔在镜面分区,眼睛看过去阴影界线我个人感觉更直观一些,我很想知道陈先生实测两面镜子的修正值总数与理论修正值总数的正负差是多少?谢谢。

苏鲁锭
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文章 苏鲁锭 » 週日 24 6月, 2007 12:24

昆仑 寫:今有幸一睹两位大师的杰作,实在是高.陈先生可否将两镜拍摄的星点图放到网上,让众多天文爱好者学习欣赏.谢谢!
不可强求啊!
我将镜子寄给陈先生,请他帮我检测一下,目的是检验一下我检测的精度。以帮助我找出存在的不足,进一步提高我的水平。也是我之前说了大话“要和世界名牌比一比”。当然我今后还有信心世界名牌比一比。
想不到陈先生花了这么大的力气,还磨了1/16波长的比较镜。这已是我的分外之望了。
别人不知道我知道,仔细检测抛物面是要付出相当的劳动的,更不要说另外再磨一个比较镜子。
对我的镜子的精度我不满意,对陈先生这样分外仔细的检测是我之前不敢奢望的。

苏鲁锭
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文章 苏鲁锭 » 週日 24 6月, 2007 12:31

呵呵!各位:
我不是怕陈先生贴出二个镜子的星点图出我的丑。
如果陈先生有机会贴出我的镜子的星点图我将不胜感激(这只能是我的又一个非分之想)。这样我可以和我在检测时看到的星点图比较。因为我现在用的是0。06MM的星点。不是0。005MM的星点。

Chanlunlun
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文章: 3833
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文章 Chanlunlun » 週一 25 6月, 2007 08:45

昆仑 寫:今有幸一睹两位大师的杰作,实在是高.陈先生可否将两镜拍摄的星点图放到网上,让众多天文爱好者学习欣赏.谢谢!
Dear Mr/Miss QingLun,

Unfoertunately we don't have sufficient equipment to make such pictures. There are difficulties :-

1. The therorectical Airy disc diameter of and 8 inch mirror is about 0.6 arc sec which demands very steady atmosphere for shooting, in order to see the disc and surronding rings.

2. After shooting the picture must go through some image processing which, unfortunately, cover up the minute difference between the two mirrors ( we are talking about a difference of 1/16 wave to 1/20 wave!!! )

3. Finally, and most importantly, we don't have such a good equatorial mount that have motor vibration smaller than 0.5 arc sec ( Even a Takahashi EM-1, EM-1s cannot do it, I don't know whether a EM-11, EM-200 could do it but we don't have two such units identical ) making comparision impossible. All previous star tests were carried out by using hand slow motion tracking to avoid motor vibration. Not shooting is possible undersuch arrangment.

We do hope that a true AB star test, visually, could be carried out shortly, to arrive at final conclusion.

Best regards
Chan Yuk Lun

TONGKW
中子星
文章: 1925
註冊時間: 週二 13 9月, 2005 14:35
來自: Hong Kong

文章 TONGKW » 週一 25 6月, 2007 21:15

陳先生致昆仑先生/小姐 (粗略翻譯)
我們不幸地沒有足夠的設備來做出這些影像。是有以下的困難:-
(1). 壹只8英吋口徑反射鏡其理論上的艾里斑直徑大約有0.6弧秒,此需要十分穩定的大氣來進行拍攝使能夠見到光斑及週圍的環圈。
(2). 拍攝之後的影像需要經過圖像處理因而不幸地會掩飾2只反射鏡之間的微小差異(我們所談及只是1/16波至1/20波的差異 !!!)
(3). 最後及最重要是我們没有這麽良好的赤道儀其馬達的掁動小於0.5弧秒(甚至高橋廠的型號 EM1 及EM1s 也不能做到,我不知道型號EM11及EM200可否做得到但我們没有2台這類相同的赤道儀)因而使這比較不可能得以辦到。所有以前的星點檢驗均是用手動微調追蹤來避免馬達的掁動因而拍攝在該情況之下是不可能。
我希望能在短期内進行壹項真正的A與B星點檢驗,只用目視,來得出最終的結論。
最後由 TONGKW 於 週二 25 11月, 2008 23:24 編輯,總共編輯了 1 次。

苏鲁锭
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文章 苏鲁锭 » 週二 26 6月, 2007 06:23

TONGKW:谢谢!!

李幽灵
星際雲
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註冊時間: 週五 25 1月, 2013 10:08

文章 李幽灵 » 週五 17 1月, 2014 21:51

其实这个检查方法早在一年前我也用过,后来也检测准直镜检测下来的镜片,确实有出入。而后我用遮光罩检测的镜片后来跟准直对比,我觉得应该是遮光罩软件逊色于准直检测。

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