... in the auditorium that is. Some of you may recall this series of
shots from my grandaughters' dance recital in 2007.
<http://www.chucknorcutt.com/dance_recital_2007/index.htm>
There was a similar recital in 2008 but I didn't like any of the shots
and hadn't processed them at all. Actually, "didn't like them" is a
serious understatement. Motion blur was everywhere due to low light
levels and very slow shutter speeds. Finally my oldest granddaughter
bugged me to prepare some 33 images for her where she either appeared in
them or she liked them for other reasons. Those can be seen here:
<http://www.chucknorcutt.com/dance_recital_2008/index.htm>
In going through them I became even more painfully aware of the
difference in light level between the two events but couldn't figure out
why it should be. In 2007 I had set the camera at ISO 3200, shutter
speed at 1/160 (for a 28-80/2.8 lens) and ended up shooting most images
at from f/4 to f/5.6. In 2008 I tried the same thing but quickly found
that I couldn't maintain 1/160 shutter speed. I was shooting at either
f/2.8 or f/3.2 and at 1/80 or 1/60 second or even much slower. With
fast moving dancers it was very difficult. I found myself trying to
anticipate when the dancers would be be coming to a halt in order to
reverse direction but not always very successful at all.
Finally I extracted the EXIF data from all the photos from both years.
I averaged the shutter speeds and apertures from all the images and
found that there was approximately 1-2/3 stops difference between them.
I also noticed that in the 2008 series that I had (very soon in the
shooting) accidentally set a -1/3 stop exposure compensation level by
brushing that silly big dial on the back of the Canyons because I hadn't
locked the settings.
The next question was: Why would there be such a great difference in
illumination level? Certainly the light level varies from scene to
scene on the stage but for the overall performance to have much dimmer
stage lighting didn't seem to make sense. I queried Dr. Flash on the
subject who reminded me that all light (not just flash light) falls off
in proportion to the square of the distance. "I know", says me "but I'm
pretty sure I was sitting about where I was the previous year". "Prove
it" he says.
I asked my wife where she thought we were sitting in 2008 relative to
2007. "I think maybe 3 rows further back" she says. That squared with
my impressions as well. So I dragged out a couple images from both
years, both shot at 80mm and compared the image height of people at
center stage. Knowing their approximate height allowed me to estimate
that the center of the stage in 2007 was about 40 feet away from us.
But the center of the stage in 2008 was about 65 feet away. Well, that
was a big surprise. 25 feet was a lot more than 3 rows back. In fact,
that's about 1-1/3 stops. Close enough to tell me that my gross
estimates of exposure and distance were close enough to explain the
cause of the problem.
So, when you take your camera into the auditorium sit as close as you
can to the stage. Just like flash, seemingly small changes in distance
can have a major effect on the amount of light you have to work with.
In my case it went from pretty good to awful by moving back 25 feet.
Chuck Norcutt
(with assistance from Dr. Flash)
--
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