1.25” Herschel Wedge Solar Prism

[Wah!!]

我記得好似見過陳倫倫及外國網頁有人用無鍍膜的牛頓鏡觀測太陽(當然也要加目鏡前濾鏡!), 應該是利用了相似的原理來減光.

[TONGKW]

佢主要係由 4%反射上減少uv/ir, 還是目鏡前濾鏡上減低uv/ir呢?

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我相信各方面都將UV/IR減小，但如何減小則實在不知道。我也有興趣想知道，我會嘗試去找尋有關資料？。
為安全計，我那套用在目鏡前的 ND3 及 Polarizing 濾鏡都採用德國 B&W 的。外國的同好多年來都這樣使用 Herschel Wedge SolarPrism 觀測太陽白光表面及黑子，也是從來没有問題，也從來没有聽過有意外或傷亡報告。我也安心以後長期使用。
我們這裡的同好 Amoebahydra 早些時購置了較昂貴的 Baader 2” Herschel Wedge Solar Prism，他亦經已用了很久。

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剛找到壹段由壹位著名外國專業太陽觀測作家的報告，內有說UV/IR大部份被玻璃吸收了。
http://www.cloudynights.com/item.php?item_id=109
QUOTE”Some people think that a Herschel Wedge is a very dangerous accessory to observe the Sun due to the UV and IR radiation, but I think they are wrong, because you have to remember that the deep UV radiation does not pass through a refractor lens because it is absorbed by the glass, but lets assume that a small percentage could get through, well that is taken care by the type of glass used in the prism and also by the eyepiece , the same happens with the IR radiation.”UNQUOTE

[CHYeung]

剛找到壹段由壹位著名外國專業太陽觀測作家的報告，內有說UV/IR大部份被玻璃吸收了。
http://www.cloudynights.com/item.php?item_id=109
QUOTE”Some people think that a Herschel Wedge is a very dangerous accessory to observe the Sun due to the UV and IR radiation, but I think they are wrong, because you have to remember that the deep UV radiation does not pass through a refractor lens because it is absorbed by the glass, but lets assume that a small percentage could get through, well that is taken care by the type of glass used in the prism and also by the eyepiece , the same happens with the IR radiation.”UNQUOTE

I don't know whether the author of the cloudynight review is an professional astronomer but he is quite ignorant of fundamental glass properties.

Most glasses transmit down to ~350 nm (50% transmission) and they are transparent in the NIR region, 700 to 2500 nm. The heating effect of NIR cause harm to the eye.

The following link gives specification of some optical glasses
http://www.mellesgriot.com/products/opt ... _1.htm#BK7

The Herschel wedge transmits, absorbs as well as REFLECT light including UV and IR.

ND number for ND filters are referring to the visible range only, though most of them will absorbs UV and NIR as well as visible light but the transmission for NIR can be higher than that for visible light especially for the more absorbing ND filter. This is shown in the transmission curve of ND01 and ND03 filters as in the following specification:

http://www.valleydesign.com/NeutralDensity.pdf


YCH

[Wah!!]

參考返一般公認安全的太陽濾鏡,
uv隔光的數量級要是 (10^-5 % 或 10^-7) 以下
ir隔光的數量級要是 (10^-1 % 或 10^-3) 以下