(All images in this blog entry are the intellectual property of Wil C. Fry and are Copyright © by Wil C. Fry, 2011, 2008, 2007, 2006.)
As always, light is the most important element in photography. Nothing happens without light. Controlling light is the number one absolute best way to improve your photography.
But given a specific type of lighting, your camera’s settings can help you work with the light. The “exposure triangle” consists of three camera settings: exposure speed (shutter speed), ISO sensitivity, and aperture (more on aperture). This article is about exposure speed.
Simply put, exposure speed is exactly what it says it is. It’s the speed at which your exposure is made. Exposure times are measured in seconds (or, rarely, minutes). It’s the amount of time that your film / sensor is exposed to light. The larger the number, the longer the exposure. (Scroll down for example images.)
The extremes of possible exposure time are limited by your camera. For example, my camera (Canon 400D) has a limit of 1/4000 of a second on the fast end. There is no limit on the slow end, when using the “bulb” setting. Some cameras have a 30-second limit for long exposures. Others can go faster on the fast end (1/8000 or better.)
Depending on your other settings (ISO and aperture), it’s relatively easy to achieve 1/4000 during the day time and still have a properly exposed image. At night, or indoors, you may need a much longer exposure time. It all depends on the light.
Check these examples:
(The next five images were taken with a Canon EOS 400D (Rebel XTi), using a Sigma 50mm f/2.8 EX DG Macro lens. The camera was mounted on a tripod to avoid camera-shake blur at slow exposure speeds. The light is from a window on a cloudy day. Except for shutter speed, all other settings were identical.)
This first example is clearly too dark. The image was created indoors, using only window light on a cloudy day. The shutter was only open for 1/80 of a second. To properly expose the image, I need to change something. Let’s assume that I chose aperture f/8 and ISO400 for good reasons. So, to brighten the image, I need a slower exposure.
I increased the exposure time by two “stops” (doubled to 1/40 and then doubled again to 1/20). For this second image, the shutter was open four times longer than in the first example. You can see almost all the detail of this glass figurine and now can see that the cloth below is blue. But it’s still a little too dark for me.
Two stops slower, and I got what I wanted. At one-fifth of a second, both the blue cloth and the glass figurine appear just as they did to my eyes.
However, if I double my exposure time to two-fifths of a second, it’s too bright. The backdrop is now gray instead of black; the blue is faded in appearance, and I’m starting to lose details in the figurine in the over-bright areas.
At one second, I’ve almost lost the image completely.
To be honest, almost all these images could be salvaged using today’s photo-editing software. Even with DPP, the software that came free with my camera, I could make that first image look just about perfect. The last one too. Most people probably wouldn’t notice the difference, especially at the sizes presented here. But anyone who looked closely at the original sizes would see why proper exposure is better to get right in-camera.
Don’t laugh, but one of the questions I often see on photography forums is “Why are my pictures too dark?” (This is often asked about snow pictures, because the camera’s light meter is fooled by the over-bright scene.)
The answer to that is always “You underexposed the image.” Use a slower shutter speed; your images will brighten immediately. (You could also widen the aperture, or increase the ISO sensitivity.)
Another question I see often is about moving subjects: “Why are my pictures always blurry?”
The answer to that is always “Your shutter speed is too slow.” (Aperture and ISO cannot help with blurry pictures, except where they assist in giving you a faster exposure.)
Remember, as long as the shutter’s open, light is hitting the sensor, coming in through the lens. If something in front of your lens is moving, and the shutter is open long enough, they’ll appear blurry. Decrease the time that your shutter is open.
Sports photographers, perhaps more than any other type of photographer, aim to “freeze” fast-moving subjects into still images. Numbers may vary, but many sports photographers set a slow-end limit at 1/400 sec., and always strive to get faster. In dark arenas and at night, they are maxing out their ISO capabilities and using expensive wide-aperture lenses so their images will still be bright at that fast of an exposure.
For the image above, I wanted to “freeze” the flames as much as possible. I used a wide aperture (f/2) and relatively high ISO (800) in order to get the exposure time I desired.
Sometimes, though, a little blur can be what you want.
I wanted this image to give the impression of movement, as my father drove through hilly areas near Broken Bow, Oklahoma. I tried several variations of settings. Some had too much blur, others froze the moment and made it look like we were sitting still. An exposure time of 1/15 sec. seemed to work perfectly. To get an exposure that slow in the daytime, I was forced to use a very tiny aperture (f/18) and ISO200.
Using longer exposures, you can create fun images like this one:
I didn’t use fancy photo-editing tools to create this image. The only editing done was cropping (there was an ugly mark on the ceiling that I didn’t want in the image) and the duotone look (because I didn’t like the colors in my apartment at the time). Creating an image like this takes planning, and help from one other person.
My wife and I choreographed this carefully. All the lights in the apartment were turned off. My wife followed me with a flashlight from one position to another, “painting” me with light when I told her I was in position. For each spot I was in, we had to think of a spot for her to stand that wouldn’t be visible in the resulting picture. I’m wearing sunglasses because that flashlight was bright in my indoor-adjusted eyes.
It sounds like a lot of work, but it only took two minutes to set up and one minute to shoot.
If you shoot still objects and use a tripod, exposure time isn’t nearly as important to you as aperture and ISO. You’ll want to set those two first, and then use whatever exposure time gives you the amount of light you want. But if you shoot moving objects, then shutter speed is probably your first concern.
A few tips to remember:
* Only a faster exposure can keep moving subjects from being blurry
* If blur is caused by camera-shake, you can use a faster exposure or a tripod to stabilize the camera.
* Aperture and ISO can each change the brightness / darkness of an image, but only shutter speed can freeze or blur.
* Just as with aperture and ISO, proper exposure time is necessary for a properly exposed image.
(This entry is part of my growing Photography FAQ. The wording above may change at any time.)