Yes, you and CH and Marc are absolutely correct. Putting it in terms of
flash lighting the subject and the exposure being the same from
different distances snapped all into clarity. I don't know what I was
thinking. Maybe I was looking too hard for an answer to a problem which
was something I could control (my distance to the subject rather than
the intensity of the light source). It was just an unfortunate
circumstance that the subject-camera distance math worked out to support
my twisted logic.
Now I just did what I should have done in the first place. I put a
bunch of thumbnails from both events on the screen side-by-side in a
browser. It's perfectly clear scrolling through those thumbnails
side-by-side that, just as CH said, the overall illumination level of
the 2008 event is considerably less than the 2007 event. And it's not
simple underexposure. Most frames in the 2008 event have many parts of
the image overexposed in the red channel while the green and blue
channels are about two stops below the red.
The real conclusion is what I didn't want to hear. My 5D at ISO 3200
and with an f/2.8 lens are not necessarily adequate to the annual task.
Two stops will be a big hurdle to overcome.
Thanks all,
Chuck Norcutt
Ian Nichols wrote:
> 2009/1/4 Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>:
>> Are you sure? I'm not. Try measuring a light in your house with your
>> light meter. First from 1 meter, then from 1.4 meters, then from 2
>> meters. Bet you find a 1 stop drop in each measurement.
>
> Yes, but that's changing the light-subject distance, not the
> subject-camera distance. Put a piece of paper 1 meter away from a
> lamp shining onto it and take spot readings from the paper at 1, 1.4
> and 2 meters. They should be the same, no? You'd use the same
> aperture to photograph that piece of paper from each of those
> distances with a manual flash, wouldn't you?
>
--
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