Wongsir 寫:上星期日在農莊測試鏡面時有用到激光做光源, 便想起Wah 很久前寫給我的一篇文章, 便急急的在電腦找回, 我們的小發明家發現用激光筆做點光源實在是磨鏡界的一大進步,一大改革.
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緣起:
我初磨第一塊牛頓反射式望遠鏡, 認識到佛科試鏡法及光柵試鏡法. 課程所設的兩種試鏡法的光源都是用電燈泡改裝而成, 試鏡時必須直接望向鏡, 而且光度非常暗淡, 無論找尋曲率中心或者觀看鏡像都甚為不便. 改用光亮的燈泡是其中一種方法改善其中的不便, 但是我無意中發現用激光作為點光源, 可以有更好的效果. 由於激光光度強, 更可以間接觀看鏡像投影, 非常適合個人試鏡及教學用途. 還有一項非常重要的好處是製作簡單及成本低.
材料:價錢,購買地點
激光筆一支 : HKD $ 16, 鴨寮街 (可另加買電池盒及開關)
光柵(自製)
新刀片(文具店)
裝作方法 :
把激光筆前的透鏡拆除, 可能要大力一點才可移走小鏡片連蓋, 這樣便可以直接用來做點光源了.
注意:
切勿直接觀看激光光源!
Wah
29-7-2000
Dear ATMs,
No wonder a laser point source is very conveniet and certainly enables testing of the mirror in a more efficient fashion. While the extreme intensity of laser source makes easy projection of the mirror profile onto the screen it also inherent the tragedy of blinding our eye, if someone unexpectedly looking into the mirror directly.
Another disadvantage of projection is that we loss the chance of direct vision into the mirror from which we are able to detect very faint variation of contrast in determining very subtle defects. The image projected onto the screen has a very low contrast ratio, making it difficult to judge subtle defects on mirror surface.
Our eye is very sensitive to variation of contrast while at the same time possesses great dynamic range, these are the two most essential features explaining why the Foucalt test has such great precision.
Anyway if used with great caution, a laser point source should be quite a good alternative to the conventional light buld, especially accounting on the fact that we no longer need to bend to difficult position to view the mirror with a single eye under strain.
Best regards
Chan Yuk Lun
