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Re: [OM] RE: Solar Filters / John Hermanson

Subject: Re: [OM] RE: Solar Filters / John Hermanson
From: "christopher.barker@xxxxxxxxxxx" <christopher.barker@xxxxxxxxxxx>
Date: Fri, 9 Jul 99 18:42:55 +0200

~~~~~ Bov, Frank said:

>Two thoughts from yesterday's digest
>
>1) Anyone ever consider how lucky we are to have someone like John Hermanson
>participating on this list? When has he ever refrained from suggesting a
>repair that was appropriate for the person posting?
Yes, a rather unfortunate bush fire I would say

>
>2) No one should ever consider solar observation through any type of filter
>without first:
>- making absolutely sure it's a 5.0 D or higher *at all wavelengths* from
>far IR to far UV
>- checking it for any defects
>
>Many filters block the visible spectrum, but UV and IR are what fry your
>eye. That's why multiple layers of overexposed color film don't work.
>Destructive testing is certainly inappropriate. Buy from trusted sources and
>check for pinholes; they can let in enough UV/IR to damage your eyesight. If
>you find them, use a heavily pigmented opaquing fluid to cover them. I have
>a solar filter for a small telescope and the inside of my filter is covered
>with little white bumps, and I add several more every time I see a hole (I
>miss a lot).

A camera shop in the UK called Speed Graphic is selling  "Kood Stanford" CR39 
filters in sizes from 37 to 86mm which they say are safe for 200-380nm UV and 
780-1400nm IR ranges (I don't understand the wavelengths mentioned BTW).  
Prices range from £15-35.  Their telephone number is +44 1420 543366.  I have 
bought a Billingham bag from them, otherwise I have no connection with the 
establishment.

Chris

><> *** Chris Barker *** 
mailto:cmib@xxxxxxxxxxx


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