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Re: Modifying your camera so it can meter IR WAS: Is this true?


  • From: "R. C. Lacovara" <lacovara@xxxxxxxxxxx>
  • Subject: Re: Modifying your camera so it can meter IR WAS: Is this true?
  • Date: Mon, 26 Feb 2001 15:10:32 -0600

The technique below relies on the fact that there is enough response left 
to the meter after the IR-blocking filter to give a usable indication. This 
seems to be the case with the Gossen Luna Pro meter.

I have used it with the inexpensive IR-pass filters from Edmunds, and it 
seems that the IR response of this meter is about 3 to 4 stops below that 
of visible light. Nevertheless, the Luna Pro has so much metering range 
that it is still useful for IR.

In my case, I have the fiber optic probe attachment, which I use to meter 
from the ground glass of my Omega 45 D. I am thinking about ways to modify 
the FO probe so that I can easily slip the IR filter in and out.

By the way, if you peer into the aperture of the Gossen Luna Pro, you can 
see a light blue glass element... I can well imagine what that is...

Bob

At 02:28 PM 2/26/01 -0500, you wrote:
>You may not even have to modify your camera. I don't. I use a Canon A-1
>and simply meter through the filter. To find out if your camera's meter
>is IR sensitive, just put a black IR filter over the lens (89B or 87)
>making sure there is no light leakage around the outside and see if you
>get a reading. Don't do this under fluorescent lights. Point the camera
>at an incandescent bulb or go outside. If you get any reading other than
>the lowest that the meter can give, you can probably meter IR without
>modifying the camera. Not all cameras are created equal though. This may
>not work on your camera.
>
>I did a simple test. I set my ASA dial to 12,800 on my Canon. I covered
>the camera's viewfinder so stray light couldn't get in through the
>window. Using an 87 filter over the lens, I metered and exposed through
>the filter at different ASA settings. Then I processed for my usual
>time. I use HC-110 70F 5 min. I made a few prints from the negatives and
>based on that, I knew the film speed for the 87 filter. Simple. My ASA
>is 6400. I use a filter between the film rails, and meter through
>another filter that I remove to compose the shot. I always shoot on
>manual.
>
>Recently, I've done the same thing using my Minolta Autometer 3F. With
>this meter, I can place a filter over the light sensor whether I'm using
>the meter as a reflected light, incident or flash meter. Using this
>meter, I have to set the ASA to 3200 to get the same results as my Canon
>at 6400.
>
>David
>*
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