Re: critique on infra article and more questions

["Christina Z. Anderson" <tracez@xxxxxxx>]

Finally I got it now, Bertha!
Chris 
> NO, NO, that's not what I meant. I apologize if it was not clear. (I
> should never reply to e-mail after a glass of wine.)
> 
> What I was trying to say is that the filter INCREASES the PROPORTION of
> IR to visible light reaching the film. The filters block some, most, or
> all visible light while allowing most of the IR to pass through.
> (Different filters pass different amount of the various IR wavelengths.)
> So the TTL meter thinks it has to increase the exposure to allow more
> visible light (i.e. what you would need for the correct exposure on
> regular B&W film) but you don't want more visible light because you'll
> also get more (too much) IR light for IR film. That's why you have to
> compensate for the filter, by changing the camera settings manually
> (changing ISO, using exposure compensation, if your camera has it, or
> whatever) to trick the meter, because even if it can read IR light, it's
> programmed to expose primarily for visible light for regular B&W. Think
> what kind of exposure you would need to get an image on Tri-X if you
> were using an 89 vs. no filter.
> 
> At least, this is the way I understand it.
> 
> Bertha
> 
> 
> 
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