Re: Wratten 87c filter

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

On 25 Feb 99 at 17:24, shopper@xxxxxxxx wrote:

> Date sent:      	Thu, 25 Feb 1999 14:38:02 -0500
> From:           	Hondo <btl3@xxxxxxxxxxx>
> To:             	infrared@xxxxx
> Subject:        	Wratten 87c filter
> Send reply to:  	infrared@xxxxx
> 
> 
> . I want to get a more opaque filter, like the 87 or 87c. If I get
> > one, what is a good place to start as far as f-stops and shutter speeds
> > are concerned? I'm not sure if I'll have to expose longer with this type
> > of a filter. I could use a little help here.....  thanks!  
> 
> Brian,
> Kodak recommends an ISO of 10 with HIE and Wratten 87c.  However, I 
> would suggest taking another step and mounting your filter behind the 
> shutter--so you can continue to focus.  You can go even another step and 
> meter through 87c material at an ISO of about 3200 using D-76 by the book.  

When metering through a dark IR filter, you can't state an exact ASA
value (ISO is DIN & ASA combined) without telling *which* meter you
used....whereas meters might not deviate much in the visible range, 
they do deviate significantly in the IR range, affecting this ASA 
value.
My Gossen Sixtomat Digital for example is happy with 400 ASA.
The more insensitive the meter is for IR, the higher you have to set 
the ASA value....with modern AE/AF cameras taking the first place.

> See Andrew Davidhazy's site: http://www.rit.edu/~andpph.  WJ is a good 
> source for 87c polyester material.

I have some notes & explanations about the BTFR (between the film 
rail) application on my homepage too:

http://www.a1.nl/phomepag/markerink/mainpage.htm

 

--                 
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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