Bracketing and How To Use
It Correctly...
By: Panmo Berger
 What
Is... Exposure Bracketing
Exposure bracketing is a simple
technique professional photographers use to ensure
they properly expose their pictures, especially in
challenging lighting situations.
When you expose for a scene,
your camera's light meter will select an aperture /
shutter speed combination that it believes will give
a properly exposed picture.
Exposure bracketing means that
you take two more pictures: one slightly
under-exposed (usually by dialing in a negative
exposure compensation, say -1/3EV), and the second
one slightly over-exposed (usually by dialing in a
positive exposure compensation, say +1/3EV), again
according to your camera's light meter.
The reason you do this is
because the camera might have been 'deceived' by the
light (too much or too little) available and your
main subject may be over- or under-exposed. By
taking these three shots, you are making sure that
if this were ever the case, then you would have
properly compensated for it.
As an example, say you are
taking a scene where there is an abundance of light
around your main subject (for example, at the beach
on a sunny day, or surrounded by snow). In this
case, using Weighted-Average metering, your camera
might be 'deceived' by the abundance of light and
expose for it by closing down the aperture and/or
using a faster shuter speed (assuming ISO is
constant), with the result that the main subject
might be under-exposed. By taking an extra shot at a
slight over-exposure, you would in fact be
over-exposing the surroundings, but properly
exposing the main subject.
Another example would be the
case where the surrounding might be too dark, and
the camera exposes for the lack of light by either
opening up the aperture and/or using a slower
shutter speed (assuming ISO is constant), then the
main subject might be over-exposed. By taking an
extra shot at a slight under-exposure, you would in
fact be under-exposing the surroundings, but
properly exposing the main subject.
 Now,
most digital cameras have auto exposure bracketing,
meaning that if you select that option before taking
your shot, the camera will automatically take three
shots for you: one which it thinks it has perfectly
exposed; a second one sightly under-exposed; and the
third one slightly over-exposed.
When should you use exposure
bracketing? Anytime you feel the scene is a
challenging one (too much highlights or shadows) as
far as lighting is concerned, e.g. sunsets are
usually better taken slightly under-exposed so use
exposure bracketing there, or whenever you want to
be sure you don't improperly expose a fabulous shot.
Remember, you are not using
film anymore, so there are really no wasted shots
(unless you are severely constrained by the size of
your storage media).
Digital Dodging & Burning
Should you delete the extra
shots right away? No, if storage permits, keep all
three shots until you get home and upload them to
your PC and into an image editing software, such as
Photoshop. By using the layers functionality of
Photoshop (or similar functionality of another image
editing software), you can load all three shots into
different layers and then carefully erase the
under-exposed or over-exposed part of one or more
layers to end up with a final shot where both the
main subject and the surroundings are properly
exposed!
This Photoshop functionality
allows you to shoot in very extreme lighting
situations where there are many parts in different
intensity of light and shadows such that you are
losing details in the highlights and shadows. In
this case, you might need more than two extra shots
to obtain details in the different parts. Without
moving the camera (a tripod is essential here), take
as many shots as you need, exposing for the
different parts you want details to be visible. Then
you would load them all up into Photoshop, each into
its own layer, and by erasing the under- and
over-exposed parts in each layer (granted, this
equivalent of film 'dodging' and 'burning' can be a
very tedious and challenging task in itself, but
done properly it can be well worth the effort), you
can end up with an 'impossible' shot where every
part of the cave is properly exposed.
Used judiciously, exposure
bracketing is a simple technique that can ensure
proper exposure of a difficult lighting situation.
Make sure you get a camera with good manual
Bracketing control
Canon PowerShot S70 - Bracketing control
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