Digital Cameras and Shutter Lag

We might as well get the topic of shutter lag out of the way immediately. That awful gap between the time when you press the shutter release on your camera and when the picture is actually taken is probably the number one complaint photographers have about digital cameras. You know the sequence: You see a great shot, put your camera's viewfinder to your eye, and press the shutter button.

Nothing happens. There's a lag of what seems to be several seconds before your camera takes the photo. That's frustrating enough when you're shooting a portrait. When your subject is an action picture, that lag can be fatal. Figure 5.2 at top shows what you saw, while the version at bottom shows the photo you ended up with.

Figure 5.2. What you saw (top) may not be what you get (bottom) when shutter lag gets into the act. 

Unless you're using a digital SLR, this is a universal problem. Under normal shooting conditions, the lag is rarely actually as long as a few seconds. I test a half-dozen cameras each month for CNet Networks, and formal shutter lag evaluations are part of the process. The non-SLR cameras average 0.6 to 0.9 seconds in lag time when shooting photos under high contrast lighting (which makes it easy for the camera's autofocus system to lock in). Under more challenging low contrast illumination, the best of the breed average 0.9 seconds, most clock in at 1.9 seconds, and a few choke for as long as 2.5 seconds. Digital SLRs, by the way, average 0.2 seconds or better (it's hard to measure shutter lag when it's almost non-existent), and so owners of these cameras should experience negligible delay.

In action photography, this gap is sometimes referred to as an ohnosecond, which is the interval between the time you press the shutter release, realize that the decisive moment has passed, and then your camera belatedly takes a picture of nothing in particular. I've experienced delays so long that I've actually given up on the photo because the action is over and snapped a picture of my feet. Not limited to action photography, "shutter lag" is one of the most annoying things about digital photography. Fortunately, I have several full and partial solutions for you.

First, it helps to understand why this happens. As you learned in Chapter 2, lots of things take place when you press the shutter release on your digital camera. To review, here's the sequence of events.

• When you first depress the shutter button partway, a digital camera set in programmed or autoexposure mode probably locks in the correct exposure. Depending on the complexity of your camera's exposure system, this may take a significant fraction of a second. You can minimize this by pressing the shutter button halfway ahead of when you actually want to take the photo. You may have to set your camera to a special mode that locks the exposure at this point. Some cameras have a button, like the one shown in Figure 5.3, that locks exposure, focus, or both.

Figure 5.3. Your camera may have a special button to lock in exposure and focus.

• Next, the autofocus system will seek the sharpest focus for the subject matter currently being framed. If your camera has been set to Continuous Autofocus, it may have been focusing and refocusing all the time you were framing the picture. If your camera has been set for Single Autofocus, it might have waited until you pressed the shutter button to focus the image.
• Press the shutter button the rest of the way, and the exposure is made. Some electronic and mechanical things may be happening at this step. In the electronic realm, your sensor might be drained of its current image so it can capture an image for the precise length of time determined by the electronic shutter programming of your camera. Or, if your camera uses a mechanical shutter, that device may open and close. Should you be using a digital SLR with a mirror used for viewing, the mirror will fold up to allow the light to reach the sensor, instead. All this takes time, which ranges from a lot (with a digital camera having a slow autofocus mechanism) to virtually no time at all (with a digital SLR, which has a much faster autofocus system because it's not based on reading off the sensor).
• The captured image is stored in your camera's built-in buffer RAM (almost instantly), then transferred to your digital film card (a bit more slowly, as you'll note from the flashing LED that marks the progress).

Unless you compensate for shutter lag, you might end up with a photograph like the one shown in Figure 5.4. I carefully composed a shot, waited until I could see my kids just entering the frame, and then pressed the shutter release. Unfortunately, by the time the camera snapped the picture, one of them was already out of the picture. All the stuff going on prior to exposure adds up to a delay significant enough to spoil many action photos, and other types as well. It's easy to spoil a candid portrait when you say, "Smile!" and the subject follows the smile with a frown when the picture isn't taken as expected.

Figure 5.4. The picture was snapped prior to the kids entering the frame, but this is the picture that resulted. 

Testing for Shutter Lag

Although the delay you experience when taking a photo may seem like an eternity, it may not be as long as you think. There are several ways to test for the lag time, and I'm going to show you three of them. First, there is an easy way to test just how much shutter lag you're really experiencing that you can do anywhere you can find a clock. Just follow these steps.

1. Find a stopwatch (preferred) or an analog clock with a sweep second hand. A stopwatch will enable you to time your shutter lag more precisely.
2. With your digital camera set on automatic focus/automatic exposure, frame the clock in the viewfinder. There's no need to take a close-up photo. All you need is to be able to read the hands on the clock/watch. (Indeed, a close-up may slow down the focus mechanism of your digital camera.)
3. Start the stopwatch or begin watching the second hand of the clock.
4. When the second hand reaches some benchmark point (such as the beginning of a minute), press the shutter button and hold it down until the photo is taken.
5. Examine the picture, like the one shown at top in Figure 5.5. The time difference between when you pressed the shutter button and the actual time imaged in the photograph is your shutter lag.

Figure 5.5. Photograph a clock, stopwatch, or computer timer to see just how bad your camera's shutter lag is.

Repeat each of these steps using various camera settings. Try the experiment both with and without flash. Set exposure or focus manually. Use shutter priority and aperture priority modes. See what the difference is in shutter lag during each of these modes, and use that information when taking your photos.

If you have an online connection and can test your camera while seated at your computer, there's a web page created by Ed Schwartz that provides a shutter lag test. As of this writing the page can be found at www.shooting-digital.com/columns/schwartz/shutter_release_test/default.asp. It's located at the web site of Mikkel Aaland, author of some great books on digital photography and image editing. Thanks, Mikkel and Ed!

A third method, which also involves a computer, is to use an on-screen stopwatch, like the Windows application that can be found at www.xnotestopwatch.com. To use XNote Stopwatch, shown at the bottom of Figure 5.5, you should mount your camera on a tripod and point it at your computer screen. Then, use both hands to click the Start button on the utility at the same time you press the shutter release on your digital camera. The quality of the picture doesn't matter, only the results, so don't worry about correct exposure or even precise focus.

Here are some solutions for you:

• Go dSLR. This suggestion isn't entirely facetious. If you plan on taking many sports and action photographs, the near-instant response of the average digital SLR might be worth a few extra dollars to you, prompting the upgrade to a camera in this category. Most snapshooters don't want or need a digital SLR, but for serious photographers, the reduction in shutter lag might be just the extra push needed to justify the purchase of one.
• Anticipate. Press the shutter button a fraction of a second before the action peak. If you understand a sport or activity well, you'll be able to predict a key play often enough to improve your odds of capturing one in pixels.
• Shoot bursts. Use your camera's sequence mode to grab a series of photos, starting just prior to the big moment, and ending after it has passed, as shown in Figure 5.6. This method has some drawbacks that I'll discuss later.

Figure 5.6. Which shot is better—the first or second? By shooting sequences, you can take your choice.

• Go manual. Use your digital camera's manual exposure and focus settings. Preset the exposure (lighting doesn't change rapidly in most action situations) and set the focus distance to a point where you anticipate the action will take place. With the automatic features turned off, you should find your shutter lag problems dramatically reduced.
• Lock in. If you must use automatic mode, aim the camera at the point where you expect the action to happen, partially depress the shutter button, and hold it until the big moment arrives. If your camera is set to lock in exposure and focus when the button's partially depressed, pushing it down the rest of the way should trigger the actual exposure without much further delay.
• Learn from goofs. Use the lulls between exciting moments to review the images you've shot so far. Learn from your mistakes on-the-spot, and re-shoot, if you can, to correct your errors. After I reviewed the roller-coaster photo shown in Figure 5.6, I realized that I was not capturing the faces of the riders. So, I moved to a slightly higher vantage point and got the improved picture in Figure 5.7.

5.7. Taking a sequence of shots can improve your chances of capturing a big moment.

• Over-shoot. Take as many photos as possible. The more pictures you take, the better your chances of overcoming shutter lag and ending up with a picture that truly captures the action.
• Watch your buffer. Be aware of the time it takes to offload images from your camera's internal memory to your memory card. If your camera's memory is sparse, you may have to wait a few seconds between shots or a series of shots before you can start shooting again. Good pictures can be lost in the interim, so you might want to limit the number of pictures you take in one sequence if you think you might want to shoot another photo during the time your camera is downloading to the memory card. Many digital cameras provide a readout that shows how much room is left in the buffer. With non-SLRs, this may be a bar on the rear-panel LCD that expands or contracts. Digital SLRs may offer a buffer-frame counter in the viewfinder.