ISO, Shutter Speed, Aperture: Part II

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The second major element that affects how a photo will turn out is shutter speed: the amount of time the shutter is open when taking a picture. (The first element, which I discussed in an earlier post, is ISO.) Shutter speed is measured in seconds and fractions of seconds. For example, the range of my G12 point-and-shoot goes from 15 seconds to 1/2000 of a second; higher quality DSLRs can have shutter speeds as fast as 1/8000 of a second.

Shutter speed controls the ability to freeze motion when taking pictures. A shutter speed of 1/60 would probably be fine to capture someone walking, but you’d need a shutter speed closer to 1/250 to capture a runner clearly. It’s especially important in sports photography, and a shutter speed around 1/1000 is necessary to capture something like a pitcher throwing a baseball.

(Side Note: Some cameras only show the denominator rather than a fraction for shutter speed, in which case the bigger numbers would actually mean a faster shutter speed.)

Similar to ISO, there is a tradeoff:

  • A faster shutter speed allows you to capture motion better, but lets less light in.
  • A slower shutter speed makes motion blurry, but creates a brighter image.

Here are three pictures from the ice skating rink at Bryant Park, taken with varying shutter speeds.

In the first one, the shutter speed is too slow to capture the motion of the skaters, making them blurry:

Shutter Speed: 1/10 ISO: 1600 Aperture: f/4.0

Shutter Speed: 1/10
ISO: 1600
Aperture: f/4.0

A faster shutter speed freezes the action better, but creates a darker image because less light is being let in…

Shutter Speed: 1/100 ISO: 1600 Aperture: f/4.0

Shutter Speed: 1/100
ISO: 1600
Aperture: f/4.0

…so you can increase the ISO to make the sensor more light sensitive, and the resulting photo is brighter, and the skaters’ motion is still captured clearly:

Shutter Speed: 1/100 ISO: 3200 Aperture: f/4.0

Shutter Speed: 1/100
ISO: 3200
Aperture: f/4.0

The driving factor behind all three of the elements is how they affect the amount of light that is let in. ISO affects sensitivity to light and how “absorbent” the image sensor is, while shutter speed affects how much light can get in before the shutter closes down.

Next up: aperture!

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