How to use camera exposure modes
If you want to take full control of how your pictures will look, turn that mode dial to one of the creative exposure modes.
The four creative exposure modes require some decision-making from the user, by choosing one or both of the exposure settings.
These modes are often called the PASM modes, as these are the first letters of the names of the modes and are the ones etched on the mode dial of your camera.
Exposure modes: Program mode
Program (P) mode is similar to the green Auto mode in that it takes care of both aperture and shutter speed, but Program allows a degree of override.
You can add fill-in flash if required, and use the Program Shift facility to change the aperture and shutter speed combination chosen by the camera (to adjust your depth of field, for example).
Simply scroll through the combinations available until you get the one you want, but the overall exposure value remains the same whichever you choose.
Exposure modes: Aperture Priority
Marked A or Av on the mode dial, in Aperture Priority mode you have to manually select the aperture you want to use, and then the camera sets a corresponding shutter speed that will produce a correct exposure.
This mode asks you to decide at the outset how much depth of field you want before you shoot. If you need a lot then you’ll set a small aperture, if not then a wider one will suffice.
The danger with Aperture Priority is that if you don’t keep an eye on the shutter speed read-out you might find that it has drifted down to a level slow enough to cause camera shake.
If you find the light levels not bright enough for the aperture you want, you’ll either need to choose a wider aperture, raise the ISO or use a tripod or flash.
Exposure modes: Shutter Priority
Marked S or Tv (for Time Value) on the dial, in this mode the camera leaves you to set the shutter speed you require, then it adjusts the aperture as necessary.
Ideal for moving subjects, this mode gives you the power to decide how the movement will be recorded: frozen sharp, or with some motion blur?
If you choose a speed too high for the conditions, you’ll get a warning from the camera, in the form of a flashing aperture. As with Aperture Priority, you’ll need to either choose a different speed, raise the ISO or use flash or a tripod.
Exposure modes: Manual Mode
In Manual you set both the aperture and shutter speed yourself. All the camera does is provide a meter reading to show what settings it thinks you should use.
If you set something different, the reading tells you how many stops it thinks you will under or overexpose by.
Because the exposure will not change from shot to shot, even if the subject or light level does, Manual mode is ideal when you need perfectly consistent exposures – say, when shooting a series of shots to join up as a panorama.
If there are exposure variations between shots (perhaps because there is something bright or dark in one of them that affects the meter reading) it will be harder to produce a seamless join. Or perhaps when panning a subject that’s moving past a backdrop that’s constantly changing in brightness. You’ll need to keep an eye on light levels to make sure they don’t change.
Manual is also best for studio use where the light is consistent; once you’ve got the first shot right all the subsequent ones will be the same.
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