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,
and the second one slightly over-exposed, 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.
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.
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