Back To Basics - Exposure: The Great Balancing Act - 2 of 5

Shutter Speed

In the introduction, we talked about balancing shutter speed, aperture and sensitivity to collect the desired amount of light for the particular photograph you have in mind. However, the ability to balance these elements requires an understanding of the benefits and drawbacks of using each. In today's article we discuss shutter speed.

Back when I was wrapping my head around shutter speed the following analogy came to me, and I have since used it to explain shutter speed to a number of folks. Think of a water faucet and a bucket. If you open the valve on the faucet water starts filling the bucket. The longer the valve is open, the more water fills the bucket. Similar to the faucet and bucket, when we open the shutter on our camera, light starts being collected by the film or digital sensor. The longer we leave the shutter open, the more light we collect. The more light collected the more exposed (brighter) the photograph. We've said that the goal in terms of exposure is collecting the right amount of light to achieve your desired photographic result. Increasing or decreasing our camera's shutter speed provides one option for regulating the amount of light we collect for a given photo, but it doesn't come without trade-offs that must be considered.

Trade-Off: Capturing Motion

Based on the description above, one might think that exposure is as simple as shortening or lengthening the amount of time we leave the shutter open, but shutter speed has a characteristic directly tied to it - the ability to capture (or freeze) motion. In an ideal world (strike that, ...in a very, very boring world) all our photographic subjects would be completely still. In these cases, leaving the shutter open would simply collect more and more light reflected off the subject until you had your desired exposure. However, waves crash on the shore, fireworks explode in the sky, runners cross the finish line, and (the most elusive) toddlers smile for fractions of a second at the camera between bouncing off the walls. In all of these cases, leaving the shutter open not only allows more light into the camera, but it also captures all of the motion in the scene. Artistically, captured motion may be your desired result; however, understanding its direct correlation to shutter speed is fundamental to being able to intentionally balance our three basic tools (shutter speed, aperture, sensitivity).

In order to illustrate this concept of "captured motion" I set up the camera on a tripod, and shot a car passing through my field of view at nine different shutter speeds. The car is traveling at 55 MPH, that's about 80 feet per second, or just slightly slower than a three year old can move from one toy to another.

You can click on all of these pictures for a more detailed view... it would probably be worth your time to do so, but I'll leave that up to you.

Shutter Speed: 1/30 sec, I'm not going inundate you with a great deal of math, but during this 1/30 of a second, the car has moved almost 3 feet. The resulting motion is captured in the elongated streak of the car.

Shutter Speed: 1/60 sec

Shutter Speed: 1/125 sec

Shutter Speed: 1/250 sec

Shutter Speed: 1/500 sec, In my opinion, this is the first photograph in which the larger features of the car have an acceptable level of sharpness for a basic snapshot. The reason: In 1/500 of a second, the car has only moved about 2 inches during the photograph. Blur still certainly exists, but finer details like the spokes on the tires start to appear.

Shutter Speed: 1/1000 sec

Shutter Speed: 1/2000 sec

Shutter Speed: 1/4000 sec

Shutter Speed: 1/8000 sec, Now we're tack sharp. Zooming in reveals that even the spokes on the wheels are nearly motionless. The math explains why, in 1/8000 of a second, the car has moved less than 1/8 of an inch. In terms of general photography, we've essentially frozen the car's motion completely.

As I mentioned yesterday, there is no "right" and "wrong" for these photographs. What is important is understanding that the trade with letting more light into the camera by using shutter speed is that the resulting motion during the open shutter is captured in your photograph.

Tangent: There is additional motion introduced into a scene as well. This motion isn't introduced by the subject, it's introduced by the photographer. Shaky hands, breathing, your heart beat, all of these move the camera and in turn introduce motion. I personally have a hard time hand holding a shot at 1/15 second. (My wife, Rose, on the other hand, likes to show off and turns out stunningly sharp photos at 1/15 sec all the time just to rub it in... but I digress) This "camera shake" as it is often called, needs to be considered as well as part of the shutter speed/motion capture balance.

Firework bursts on the Fourth of July, a waterfall, an ocean wave, a shooting star across the night sky, the checkered flag at the Indy 500... These are just a few of the many different situations that require different shutter speeds. Experimenting with your camera is always the best way to learn the correlation between what shutter speed is necessary and what result you desire.

Alright, let that stew until tomorrow when we dive into understanding aperture.

Tomorrow: Aperture