Smart Photography 201707

Exposure Modes

M

ost cameras allow us to shoot

using different exposure

modes – Aperture priority

(A), Shutter priority (S), Program

(P) and Manual (M). On Canon

cameras, Aperture priority is known

as Aperture value (Av) and Shutter

priority is known as Time value (Tv).

Some cameras also offer Scene modes

but in this write-up, we shall not be

discussing them. Let’s see how the A, S,

P and M modes work and when should

we use them.

An exposure is basically a product of

ISO sensitivity, aperture and shutter

speed. You first set the ISO sensitivity

depending on the brightness of the

available light.

Aperture priority mode

(A or Av)

Apertures control the quantity of light

entering the lens. They also control the

depth of field (the zone of acceptable

sharpness in the picture). When

using Aperture priority, you select the

aperture of your choice depending on

the depth of field that you desire and

the camera will automatically select

the appropriate shutter speed.

Note: Even though the camera

automatically selects the shutter

speed to match the set aperture, you

need to keep an eye on the selected

shutter speed; too slow a shutter

speed will cause camera movement

during the exposure, resulting in a

blurry image. If that happens – if the

indicated shutter speed is too slow

for comfortable

hand-holding

• you can do
  one of the three
  following things:

a) Use a wider

aperture (but

your depth of

field will reduce)

b) Support

the camera

on a suitable

platform (use

a tripod; but

remember,

that will not

stop subject

movement)

c) Increase the ISO sensitivity (your

image could be noisier)

Shutter priority mode

(S or Tv)

The shutter speed controls the

duration or for how long the shutter

remains open (this in turn will depend

on the ISO as well as the aperture that

you have set). So in a way, the shutter

speed also controls the exposure.

The shutter speed does something

else too; depending on what shutter

speed is used, it can freeze movement

or create an impression of movement

in our still images. Fast shutter speeds

will arrest movement; slower shutter

speeds will create an impression of

movement.

Should you use Aperture

priority or Shutter priority?

The choice is yours. If control over

depth of field is more important to

you, consider Aperture priority. If

freezing action or creating a feeling of

Rohinton Mehta

LEARNING

98 http://www.smartphotography.in

Smart PhotographyJuly 2017