re: critique on infra article and more questions

[Bertha Adamson <badamson@xxxxxxxxxxxxx>]

Subject: critique on infra article and more questions
Date: Thu, 26 Oct 2000 13:47:02 -0600
From: "Christina Z. Anderson" <tracez@xxxxxxx>
Reply-To: infrared@xxxxx
To: "Infrared Photo" <infrared@xxxxx>

Thanx for the interest in critiquing my infrared article.  I received
about
25 requests for it (was very surprised)(whew) and have received back
about 4
critiques of it.  Please continue to send me back your input.
     Bertha raised an interesting question.  Does putting a red filter
on
your lens INCREASE the amount of infrared light available to the film?
From
what I understand of filters this is not so, it just decreases the
visible
light it blocks.
     Is there truly no difference with Konica with the 15, 25 and 29
filter?
     Do fluorescent lights in the darkroom that take a while to subside
truly not fog infra film if you turn them off and immediately start
developing, e.g. in trays in the dark?
     Should I not even recommend Rodinal as an infrared developer
because
the grain is golfball size?
     It is so nice to have you experts here to bounce these concerns off
of.
I do not want to xerox these notes for 40 students if there is wrong
info on
them.
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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