Re: Rm90 Infrared filter

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 19 Sep 99 at 3:41, danzig@xxxxxxxxxxxxxx wrote:

> 
> 
> hi! :)
> 
> 
> I need to ask, is the RM90 supposed to be Hoya's version of 
> b + w 's 092 / 093 opaque filters ?

Sortof, at least according to Hoya....
 
> The spec booklet stated that RM90 cuts at 900 region, so either 
> this is false information, or I have unusually sensitive eyes, as I 
> could see thru the filter, extremely faintly of course, made out 
> some details but couldn't focus by it. I was looking at a daylight 
> scene at rough 1 pm

Your eyes are okay, I had the same experience....the crux is in the
bottom of the spectral graph....it is very hard to distinguish
between a table that goes to absolute zero transmission in the
visible range and one that goes only to 1%....but one can clearly
see the difference when looking through a filter (1% transmission is
less than 10 stops!). 

> I thought 730 was where the infrared spectrum started. Shouldn't it 
> be completely opaque ?

IMO it does raise that expectation, even from the graph, but in 
reality it doesn't. 
Note that I have never tried to establish the 'pictorial equivalent' of 
R90, compared to the Wratten series....would be weird to classify it 
as #89B, since that is what R72 is the equivalent of....
 
> Then again my R72 is definately opaque and its supposed to cut at 
> 720 and I can definately see thru it , even in weak daylight

?
Neither #89B nor R72 is supposed to be opaque, which is confirmed in 
reality....


--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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