At 05:30 PM 11/1/1998 -0500, you wrote:
>I recently got an orange filter for B&W photography, thinking it would be a
>good compromise between a yellow and red. I've always just metered through
>the filters on my OM1, expecting that the in-camera meter would correct for
>the decreased light. While using this filter, though, I didn't seem to be
>losing as much light as I thought I should (I was expecting maybe 1 to 1.5
>stops). In fact, the meter indicated less than half a stop change when I
>put the filter on. (BTW, this is a Hoya HMC O (G) filter.)
>
>This leads me to the conclusion that perhaps the OM1 meter is primarily
>sensitive to light at the orange/red end of the spectrum. Does anyone else
>have any experience with this? I'm thinking that perhaps some adjustment of
>the ASA dial may be needed with this type of filter.
>
>Perry Bain
>bainp@xxxxxxxxxxxxxxxxxxx
>
Hi Perry,
I have always noticed the phenomenon you describe. I hope one of the
physics guys will weigh in here, but I do recall in reading about filters
long ago that it is not safe to expect the meter to account for the "filter
factor" automatically. Ansel Adams wrote in his first series book on _The
Negative_ (p.26): "Use of a color filter may raise or lower tonalities,
supplementing the effect of exposure-development control." Your orange
filter in effect darkens your greens and blues; it lightens your reds,
oranges, and yellows. This has got to affect your meter as compared to
normal, depending on the preponderance of colors in your field of view. My
experience with both red and orange filters is that metering through them
will almost always result in an underexposed negative. The only way to get
the intended good from your filter is to determine the correct exposure
without the filter and then open up the pre-determined amount as indicated
by the filter manufacturer, which in the case of the orange filter is just
under 2 stops. You can vary this factor, but you should know what to expect
through experimentation before you do so.
Hope this helps. Others can undoubtedly give you a better technical answer.
Joel
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