Exposure Trio Part Three: Shutter Speed

The Exposure Trio

A Three Part Series

ISO—APERTURE—SHUTTER SPEED

Part Three: Shutter Speed

Welcome to the final part of our three-part series.

To review, in Part One we talked about ISO. As you will recall, similar to film speed, ISO is a measure of how sensitive our digital sensor is to light. The goal is to keep the camera set at as low an ISO as possible to limit digital noise.

In Part Two we discussed aperture. Aperture refers to an adjustable iris inside the camera lens that controls the size opening we allow light to pass through. This is adjusted by changing the aperture size as measured by f-stops. We also learned how to use aperture creatively by controlling depth of field.

In this, Part Three, we are going to talk about shutter speed.

Simply defined; Shutter speed is how long we expose the camera’s sensor to the light passing through the lens aperture opening. Think of it this way, each time you take a picture a curtain opens in front of your camera’s sensor. Shutter speed simply refers to how long we allow that curtain to remain open.

Today’s cameras can set shutter speeds ranging from fractions of a second, to in some cases, as long as thirty minutes. Many cameras also feature a “bulb” setting that allows the photographer to keep the shutter open as long as the release remains depressed.

Shutter speed settings are easier to comprehend than f-stops. For example, a 1/30th of a second shutter speed lets light strike the sensor for twice as long as a 1/60th setting, but only for half as long as a 1/15th of a second. And a 1 second shutter speed lets in twice the light as a half second, which in turn allows in twice the light as a 1/4 second setting.

As long as you can manage easy fractions, you can understand the mechanics of shutter speed.

I also think it’s important to review shutter speed in relationship to aperture.

Let’s for a moment pretend we are making a portrait in a room where the light remains constant. We will also assume the ISO setting on the camera will not change.

I set my camera to shutter priority mode (S for shutter, or Tv for time value) and select a shutter speed of 1/250th of a second. When I depress the shutter release partially the camera meters the scene and tells me at 1/250th the aperture will be set at f/2.8.

I determine that f/2.8 will not allow enough depth of field to capture my entire portrait in sharp focus. Now what?

Simple, I opt for a slower shutter speed, which in turn allows for a smaller lens opening and more depth of field.

For instance, if I slow my shutter speed to 1/125th of a second I am now doubling the time light strikes the sensor. Which in turn means I can stop the aperture down one stop to f/4 allowing in half the volume of light as f/2.8. I have doubled the time the shutter is open, and then halved the amount of light passing through the aperture opening, with the end result being the same amount of light reaching the sensor. And of course, f/4 gives me more depth of field than f/2.8, problem solved.

For any photograph there will be multiple combinations of shutter speed and aperture that result in a correct exposure. It’s our job as photographers to determine which combination we want to use.

We know from Part Two of this series that you prioritize aperture choice when you want to control depth of field.

So when do you prioritize shutter speed?

Shutter speed not only controls how long we allow light to strike the sensor, it also allows photographers to stop or blur subject motion.

A football player running down the field, the Ferris wheel at the county fair, a cascading waterfall, a child on a swing are all examples of moving subjects. Anytime you photograph a moving subject you must decide if you want to freeze that movement, or allow the camera to record a degree of motion blur.

A picture of a baseball player sliding into home would not be acceptable if too slow a shutter speed caused the entire image to be an unidentifiable blur. And a picture of a rotating Ferris wheel may be boring if a fast shutter speed froze its motion as if it were standing still.

To freeze the motion of a moving subject you will need to experiment with faster (shorter) shutter speeds until the shutter speed is fast enough to stop all motion blur in the photograph. If the picture would benefit from subject motion blur you must experiment with slower (longer) shutter speeds until the blur suits your creative tastes.

I have included a series of images taken of a simple ceiling fan to illustrate how shutter speed choice impacts motion blur. As you can see, as the shutter speed becomes slower, motion blur increases. Is any one of these pictures taken with the correct shutter speed?

The answer is they all are. As a photographer it is your creative choice to blur or not to blur.

In future blog posts I’ll talk in detail about the use of shutter speed and aperture for particular types of photography. For now I hope you have learned that aperture controls depth of field, and shutter speed controls motion. And lets not forget, ISO choice determines the range of shutter speed and aperture combinations we have available to us in any given situation. When you need a faster shutter speed or a smaller aperture than the available light allows, then and only then, raise your ISO from your camera’s lowest ISO setting.

Until next time,

RG

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2 Responses to “Exposure Trio Part Three: Shutter Speed”

  1. HGC Effects Says:

    That is really intriguing. It gave me a few ideas and I’ll be posting them on my blog shortly. I’m bookmarking your blog and I’ll be back. Thanks again!

  2. rommelrutor Says:

    Reblogged this on Words and Images.

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