Re: Filters

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

On 21 Feb 00 at 14:36, Dan Vint wrote:

> Actually the answer isn't there, that was why I was asking. At least I
> didn't find a mapping from Wratten to anything.
> 
> I did find that an 87c is a 093 in B+W and an 89B is an 092 in B+W and
> Wratten 12 is a 099 B+W.
> 
> It doesn't appear that Tiffen has any IR filters 

Could have sworn they had a single #87C, but can't find that anymore 
in the B&H catalog....the darkest red is a #29.

> and I found the Hoya (2
> filters) but they aren't rated to the Wratten system.  Hoya has an R72 that
> passes IR above 720nm and an RM90 that passes above 900nm - which I guess
> makes the
> R72 an 89B and the RM90 somewhere between an 87c and 87b.

The R72 indeed equals a #89B, but the R90 is odd....it doesn't block 
visual light completely, it looks more like a #88 (slightly darker 
than #89B). Note that this only refers to its visual effect, in IR it 
probably indeed blocks better than R72, but it is definately not as 
visually opaque as a  #87B or #87B (even a #87 or #88A is already 
opaque to the eye). 




 

--                 
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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