Exposure compensation is function that allows you, the
photographer, the ability to fine tune exposure to compensate for situations
where your camera's metering system does a poor job.
This would be something that you would want to use to make
adjustments for contrasting light when highlight detail would otherwise be
lost, or when photographing snowy landscapes or other tricky scenes. This photo
that accompanies this post is a good example of a real life situation.. the crashing
water was extremely bright, and the kayaker had a helmet on that casts a very
dark shadow across his face. I had to use my exposure compensation to ensure
that I did not either blow out the water, or make his face black. It took a few
photos to get the right setting, but it was worth the effort.
Cameras are programmed to just aim
for the middle of the grey scale… A camera exposes for the middle luminance
value of the scene (middle grey, 12-18% reflectance or 50% luminance), and your
cameras different metering modes are just different ways of placing this mid
value by weighting where the camera meters from.
EV Compensation helps to fix this by telling the camera to
expose at a higher or lower setting than it thinks is right. For very bright
settings (like the snow or beach), set an EV value as a positive number (+1/3,
+1 etc). For very dark scenes, choose a negative EV number.
Now, I know what you’re thinking – that doesn’t make sense! If the subject is very bright, don’t I need to set a lower EV (negative number) to make sure the image is exposed correctly?
Well, no. It’s the opposite. It helps to think of what the
resulting image will look like. In the snow, where there are lots of bright
areas, the camera will choose a mid point in the bright area, so the snow will
look gray in the resulting image. To fix that and make the snow white (as it
should be), we need to brighten the image. Thus we need to increase the
exposure and use a positive number.
You would need to consider using exposure
compensation in the following situations:
Landscape photography in bright, sunny conditions - Landscapes
are usually shot at wider angles (zoomed out) and often includes bright skies
and dark shadows. Your camera's estimate of the mid value in such contrasty
situations can often result in important highlight details being be lost in the
sky because of that orange ball of bright light, aka the sun. To remedy this,
you would darken the image slightly by reducing exposure, usually by two or 3
stops. This will lighten the shadows and bring those awesome colours back in
the sky that drew you to the image in the first place.
Snowy scenes - Snowy scenes are unusually white, and your
camera will think this is supposed to be more towards mid grey. Without an
adjustment your white fluffy snow comes out this pale blue… sound familiar? To
remedy this, you would lighten the image by increasing exposure by 1 or 1 1/3rd
EV.
Most cameras will have an EV display (in the
viewfinder or on-screen). The zero in the centre is where no EV compensation is
applied; to the left we have -EV and to the right we have +EV, with 1/3rd EV
steps between.
Depending on your camera and display settings, the EV
display may only show when in use, or when compensation has been applied.
In Aperture Priority, Shutter Priority or Programmed Auto
Locate your camera's EV button (marked EV or +/- ), hold it
down and scroll the relevant command wheel either +right or -left depending
whether you wish to increase or reduce exposure (lighten or darken the image).
As you scroll, the marker will move to the corresponding value on the scaled
display, or the value will simply update on the single type display.
Remember to set the EV back to zero once you've finished
taking exposure compensated shots.
Manual Exposure
In fully manual, you set the shutter speed and aperture
values, and the EV display tells you how much this may differ from what the
camera's metering suggests. The EV button isn't used, but the effect on
exposure is the same.
The advantage with manually applied exposure is that you
don't have to remember to reset compensation. You do, however, have to set
exposure yourself for each shot.
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