Exposure is the process of choosing the correct settings on your camera to produce a picture that “looks right;” not too bright, not too dark, and sharp where it should be. In this series, you will learn what each setting means, how they affect the way your images look, and how they work together to create an image that matches your creative ideas. In this article, we dive into the shutter speed setting, what it represents, and how to use it in your photography.
What is the shutter?
The shutter is like a door in front of your sensor or film in your camera. When you press the button on your camera to take a picture, this door opens, letting light hit the sensor (or film). The longer this door is open, the more light is allowed to hit the sensor, creating a brighter image. Traditionally, the shutter was a mechanical device that literally opens up to expose the sensor or film to light. While mechanical only versions are still used in many DSLRs, as technology evolves these are being replaced with hybrid electromechanical or fully electronic shutters that power-on the sensor. If you a have “Live View” of some form on your camera you are seeing an electronic shutter at work.
The length of time the shutter is open is termed the “shutter speed,” this along with the other two sides of the triangle above, aperture and ISO determine your exposure. Most often your shutter speed will be measured in fractions of a second. However, instead of showing the number as a fraction, most camera systems will display this setting as a number like 50 or 200 or 400, dropping the “1/” to save space on your display. If this number has a quote mark after it, that represents whole seconds. A number like 5″ or 30″ would represent a 5 or 30-second exposure, otherwise, assume it’s a fraction.
In addition to image brightness, the main effect of shutter speed is on how a subject in motion appears in your photos. Anything that moves during the time the shutter is open will appear as a blur from the point where it started at the shutter opening to the point is when the shutter closes. While this blur will be relatively unnoticeable at fast shutter speeds, the longer the shutter is open, the more extreme this blur appears. While there are many types of blurs in photography, the shutter mainly deals with motion blur, and either freezing or exaggerating it.
This blur can also be caused by your movements too. Let’s say you are taking a picture of a landscape, which is not moving. But it is in low light, you didn’t feel like using your tripod, and you thought that a triple espresso before the shoot was a perfect “pick me up.” At longer shutter speeds any shake or other motions you impart to the camera will also blur the image. But the blur will appear in the directions you are shaking or shimmying, instead of the direction your subject was moving. Combine your espresso fueled self with a moving subject and odds are very against you producing a sharp image.
This isn’t to say that blur is always a bad thing. Blurs can be used to great artistic effect to set mood, express motion, or create unique effects. Although it may be a touch cliché, think of the dreamy silky look popular in waterfall photography. This is accomplished by using a long exposure causing the water cascading down to appear as a blur, while the motionless rocks appear sharply in focus. “Pan blurs” are another artistic effect, panning with a subject, but at just a slow enough shutter speed that while they appear sharp, the rest of the scene appears blurred, giving a sense of motion.
Shutter speed in the real world
To put this idea of blur and freezing action in to real world concepts, let’s use one of my favorite wildlife subjects as an example, Sandhill Cranes. Although they are big, these feathered friends of ours can move fairly quickly. A sandhill crane typically flies between 25-35 miles per hour. I can fly as slowly as 15 mph and as fast as 50 mph. Doing a quick bit of math and unit conversions, if our crane is moving at a leisurely 20 mph, it’s still covering about 30 feet per second*. And these guys are not the fastest critters out there by any stretch! (For my fellow Monty Python fans, the crane is unladed, and no coconuts were harmed in this example).
This is where shutter speed becomes crucial. Let’s say that a sandhill crane flies across the scene in front of you. At long (slow) shutter speeds you are capturing that animal from the moment the shutter opens to the moment it closes. Any movement is perceived as blur, from the point it started in the frame to the point it ends up. If you have a 1 second shutter speed, and the camera is locked in position, you will have a streak of gray stretching 30 feet through your scene. If you use a high (fast) shutter speed, like 1/2000th of a second, you will freeze motion, as the sandhill doesn’t move very far in this amount of time, only about 1/8th of an inch.
Of course, this is all assuming you aren’t panning, or tracking the crane with your camera. In action photography the combination of smooth panning, long lens technique, and proper camera holding are critical skills to learn and to practice regularly. With these you can minimize the appearance of blur to some degree by matching your pan speed to the speed of your subject, making them appear more motionless against their motion blurred background. But, using our one second exposure example, even if you are moving fairly smoothly the odds are very slim that you perfectly match the cranes speed through a long exposure. Any variation will appear as blur, the more vertical shake or a failure to smoothly pan, the more extreme the blur will appear
Although we can fix a lot of things in our digital darkroom, fixing an out of focus photo due to motion blur is beyond our reach. This is one of the main factors in making me hit the delete key, a blurry photo gets trashed most of the time.
A simple guideline to get sharp images when hand-holding your camera is your shutter speed should be equal to or faster then the inverse of your current focal length. In other words, put a “1/” over your focal length. If you are at 400mm, you should have a shutter speed of 1/400th of a second or faster to minimize the appearance of blur from any movements you make during the exposure of your image. A few important points to remember with this are:
- This guideline doesn’t deal with movement of your subject, only you.
- At low enough shutter speeds this no longer works. We all shake to some degree, you simply cannot hand hold a 1 second exposure and expect a sharp image.
- Use a tripod. This will help to a large degree, but only if you are using good long lens/tripod techniques!
- This does not take into account any Image Stabilization or Vibration Reduction or Vibration Control (all different names for the same thing) built into your lenses or camera bodies that help stabilize and eliminate the effects of shake.
- IS/VR/VC will help reduce the movement to your camera caused by you, but does nothing to reduce blur caused by your subjects movement.
Review: Shutter speed
A fast shutter speed will freeze any motion in the scene, both your subject’s movement and any movement you cause to the camera by holding it. A slow shutter speed will cause any motion to appear as “motion blur,” the longer the exposure the more pronounced the effect becomes.
Fast shutter speed = freeze action
Slow shutter speed = blurring of action