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Exposure Compensation with DSLR
is a technique used to control the amount of light entering the lens to enhance the light distribution.
Exposure compensation adjusts the exposure according to either the aperture and the shutter speed or both depending on the camera mode, if it in Aperture priority (A.v) then the f-number changes and in Shutter priority (T.v) the exposure time or shutter speed changes, and in manual mode, both are affected. Some digital cameras may also alter the ISO if it’s set in Auto.
Exposure compensation will be used when there is a high contrast in lighting or unusual lighting distribution in the scene. Selecting the right Exposure Value (E.V) will uniformly expose both the dark and bright areas.
Exposure values are ‘stops’ that refer to various combinations of shutter speed and aperture. They may have a minimum value of -6EV and a maximum value of +6EV but common values are -2 and +2 with increments of ½ EV or 1/3 EV per ’stop’. Some cameras do have ‘stops’ of a 1 or even ¼ EV where 1EV is equal to doubling the exposure. When you increase these EV you slow down the shutter speed or widen the aperture to have more exposure and vice versa. So to darken a photograph you decrease the Exposure value (-).
Exposure compensation will be used when there is a high contrast of lighting in the scene, for instance when the subject is well lit while the background is not, the subject may get over exposed and when the subject is darker than the background, the subject will get under-exposed. Exposure compensation on the camera will allow more light from the dark-lit areas to go through in order to expose those areas hence retaining details in all areas.
In areas where is a great contrast in lighting, i.e, very bright and very dark, you will need to reduce the exposure so that you do not over-expose the bright areas since dark area preserve details better than bright areas. You can go on to edit the picture later in post-production. Also do not under expose you image too much since details will be lost in very dark areas.
There is a way employed by professional cameras to ensure to take a photograph with the right exposure, its exposure bracketing.
In this setting you take three successive shots each with a different exposure. The first shot is with the exposure compensation recommended by the camera (0), in the second shot the exposure is increased by 1 value (+1) or over-exposed and the third shot the exposure is decreased by 1 value (-1) or under-exposed. The difference in the exposure of your shots will depend on how you have set the camera in either ¼ EV, ½ EV, 1/3EV etc. With some cameras it is possible to take even up to six shot with different exposures successively.
When AEB is selected, the camera automatically takes three successive shots with different exposure in each shot. This will ensure at least one shot will be close to perfectly exposed as possible.
Exposure bracketing in Manual mode, it overrides the camera settings automatically. When you change either the shutter speed or the aperture the camera automatically shifts the exposure values of all the three shots by either increasing or decreasing. When you set a faster shutter speed or wide aperture value, the camera will automatically decrease the exposure values, and when you set lowers shutter speed or narrow aperture, the camera will automatically increase the exposure values. This is to compensate lighting.
Unlike in manual mode, in Shutter priority (T.v), Aperture priority (A.v), and Program Modes you first set your favourable exposure value manually using the shift key e.g. Canon 1100D, then you adjust the Main Knob to set vary the stop values of –ve and +ve.
For you to set the three different exposures, you will have to select expo.comp./AEB Settings, then rotate Main Knob of your camera to change the stops, failure of that all your three shot will have the same exposure compensation, i.e no difference.
OTHER TYPES OF BRACKETING
White balance bracketing
It is used to adjust the colours, it’s a perfect way to deal with mixed lighting
You can set the white balance manually, by selecting WB Shift/BKT setting on the menu, a graph is displayed, press the shift buttons/navigation keys, the left side shifts the colours towards the blue colour, right side shifts towards amber (red) colour, upper side shifts towards green while the lower side will shift your colours towards magenta.
For you to set a white balancing bracketing, you rotate the Main Knob clockwise or anti-clockwise to adjust the extent of bracketing and then shift/navigating keys to move the bracketing towards a certain colour and click OK button, or you only need to press the shutter release button once and you will get three shots with varying white balance.
To reset, you press the Display button or turn off the camera.
It is used to adjust the amount of light that the flash gives out.
On Canon 1100D, you can decrease the value up to -2 and a maximum of +2
To set on your camera, go to menu-flash control, select Built-in flash function or External flash function setting.
Flash bracketing is not automatic in many digital cameras and you will have to set it manually after you take each shot.
The ISO is changed automatically by processing the raw sensor data to give different ISI’s prior to the image being saved on the memory of the camera. The aperture and shutter speed remain constant.
NB: when you switch off the camera, all exposure compensation and bracketing settings are reset to zero.