Although it’s possible to correct minor exposure errors if you shoot raw files, lightening under-exposed shots with very dark shadows introduces unwanted noise, and you simply can’t recover completely scorched highlights. If something registers as bright white on your sensor, without any detail, no amount of editing will bring back that detail. So it’s always best to strive for perfect exposures in-camera.
The easy way to correct exposure in-camera is to use the +/- exposure compensation button. Under-exposed shots require positive compensation, and over-exposed shots require negative compensation.
If your subject is off-centre and has a very bright or very dark background, metering from the whole frame may fail to provide the correct exposure. Your camera’s Auto Exposure Lock (AE-L) facility can help here.
First, compose your shot so that your subject fills the frame, zooming in if necessary. Then, while pressing the AE-L button, half-press the shutter button to meter directly from the subject. Then, recompose and shoot (although be aware that the default setting in your camera may require you to keep the button half-pressed throughout). This technique is very effective for evenly lit subjects, but may need further adjustment. AE-L can also create difficulties if linked to focus lock – check your manual to find out how to separate them.
Even when you think you’ve nailed an exposure, with important shots it’s good practice to bracket your exposures. You can either do this using exposure compensation (see left), using manual mode, or using the exposure bracketing facility on your camera. Try bracketing shots at +/- 0.3EV, 0.7EV and 1EV (equivalent to +/- 1/3, 2/3 and one stop) each side of the metered exposure.
Bracketing basically provides peace of mind, and it’s essential when faced with a high-contrast scene that you plan to ‘fix’ later by merging exposures in Photoshop. However, it takes longer and uses up more space on your memory card.
Using manual mode
If you work in manual mode, it’s relatively straightforward to correct for exposure errors. If the image is too dark, for example, you can dial-in a slower shutter speed or choose a larger aperture to allow more light in. Many SLRs enable you to vary aperture and shutter speed values in increments as small as 1/3EV (1/3 of a stop), enabling subtle fine-tuning. It does work, but you need to have the confidence to set both the aperture and the shutter speed manually.
The exposure level indicator
Select any of the creative exposure modes on the mode dial (usually P, S/Tv, A/Av and M) and look through your camera’s viewfinder. You’ll see some numbers and what’s called the exposure level indicator – a dotted line typically marked -2, -1, +1 and +2.
In the middle of the exposure level indicator is what’s called the standard exposure index, and an exposure level mark. When this mark is in the middle of the exposure level indicator, you’ll capture a standard exposure, as determined by the camera’s meter. The scale shows any exposure compensation you’ve set, or shows you if your image is under- or over-exposed if shooting in manual (M) mode – again, based on the exposure determined by the camera’s meter.
As well as the exposure level indicator, you’ll see your shutter speed and aperture, and on some cameras, the ISO setting. You may also be able to press a button to display all this information on the top-plate LCD.
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