Balancing Light and Dark in a Low Light Situation
The problem with photographing a situation like this Dairy Factory is making
the correct exposure for both the lit windows and the darkening sky. The sky
may seem unimportant, but if it's too bright, it becomes almost a daylight
photo, diminishing the impact of the windows. Then if the sky is dark it will
merge with the roof of the building, and there will be an unpleasing black
mass at the top of the image.
Firstly, you need to find the correct exposure for the windows, this is
done by "bracketing" (that is taking several differently exposed
shots, see "About
Bracketing and Stops" below). Exposure is the combination of shutter
speed and aperture, so take some trial images using faster and slower shutter
speeds as well as whole or half stop changes to the aperture.
Having bracketed a few test images, the correct exposure for the windows
is then selected from the processed film (taking note of exposure settings in
the field is a very good practice). So, how to discover the correct sky exposure?
Revisit the site as dusk approaches. Take a series of photos as the sky
becomes dimmer using the previously selected exposure settings for the
windows.
When these shots come back from processing, it should be found that one
gives the sky the density that is sought, and the windows exposed correctly.
If you are taking a series of images and bracketing by one stop between
each image, that means that each successive image will receive double (or
half) the amount of light than the previous (or next) shot. This can be done
by altering shutter speed, for example, the following speeds are double (or
half) the adjacent reading: 1/4 sec, 1/2 sec, 1 sec, 2 secs, 4 secs, and so
on. Altering the lens aperture by the marked f values will also make one stop
difference, for example, double (or half) the amount of light will enter the
camera with each adjacent setting: f/4, f/5.6, f/8, f/11 etc., hence the term
"f stop".
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