Helping your camera cut through darkness
Whether you're shooting with a film or digital camera, taking pictures in dim lighting poses special challenges. After all, a camera works by recording the amount of light in a scene. If the camera's eye doesn't sense much light ... well, you see the problem.
Of course, one option is to use a flash or another auxiliary light source. But on many occasions, adding artificial light isn't a viable solution. Most museums don't allow flash photography, for example, and dragging along studio lights to your child's first night-time piano recital would probably get you booted by auditorium security. Even if you're under no such restrictions, a flash or other artificial light source may be too underpowered to illuminate a subject fully.
When adding light either isn't possible or doesn't solve your exposure problem, you can help your digital camera cut through the darkness in the following ways:
- Raise the ISO setting on your camera, which is akin to using a higher ISO film. As explained in the next section, however, this solution sacrifices some image quality.
- Increase the aperture size (by selecting a lower f-stop number) to allow more light into the camera. This choice also changes depth of field, causing fewer objects to appear in clear focus.
- Select a slower shutter speed, which increases the amount of time that the image sensor can gather light.
Adjusting light sensitivity (ISO)
The image sensors on most digital cameras have a light sensitivity equivalent to ISO 100 film, which means that they respond best to brightly lit scenes. In an attempt to give photographers a better chance of recording a good image in dim lighting, newer cameras offer an ISO control that adjusts the camera's light sensitivity.
The ISO control settings typically match the ISO ratings on standard consumer films: ISO 100, 200, 400, and 800. The higher the number, the greater the camera's sensitivity to light.
With a higher ISO film -- also called fast film by photographers -- you can get a good exposure with less light. In bright light, the increased light sensitivity enables you to work with a smaller aperture (higher f-stop number) or faster shutter speed than when using a lower ISO film. If you're an experienced film photographer, you know that increased light sensitivity comes at a cost, however. As you move up the ISO scale, you increase grain -- a visual defect that looks like someone sprinkled sand over your photo. The same trade-off exists with digital cameras, only in the digital world, the resulting defect looks like speckles of random colour and is known as noise.
The amount of additional noise produced when you increase ISO varies from camera to camera; your model may produce significantly more or less noise than what you see in these examples.
Raising the ISO setting results in a brighter exposure but also introduces noise,
giving the image a speckled look (right).
How much image quality you should sacrifice for increased light sensitivity is purely a personal creative choice. As you debate the issue, keep these points in mind:
- If you're shooting in programmed autoexposure (AE) mode, the camera automatically adapts aperture and shutter speed to your ISO setting. In aperture-priority AE, the camera changes shutter speed only; in shutter-priority AE, the camera adjusts aperture only. Remember that the camera can do only so much in this regard, however. If you're shooting in extremely dim lighting, you may not be able to record a good image at a low ISO even if the camera opens the aperture all the way and uses the slowest available shutter speed. Note: you may be able to brighten the exposure to an acceptable degree after the fact in your photo editor.
- Noise is typically most apparent in shadows and areas of flat colour, such as the sky. To be fair, however, at a lower ISO, you may lose all detail in the shadows. Areas that should contain a blend of dark grey to black pixels may all be recorded as black, as you can see in the window archways in the ISO 100 example in the image above.
- Some cameras offer an Auto ISO setting. In this mode, the camera automatically adjusts ISO as the light changes. I recommend that you turn off this option and select a specific ISO setting instead. Most cameras don't inform you when they change the ISO setting, and this control has too big an impact on exposure and picture quality to leave to chance.
- Check your camera manual to find out whether your model offers a noise reduction feature. This option applies a software filter to erase noise as part of the file processing that occurs as your camera stores the image. Usually, noise removal kicks in only at very slow shutter speeds, however, and also significantly increases the time you need to wait between shots for the camera's brain to do its thing.
- When all else fails, you may be able to diminish or even remove noise in your photo editor by blurring the affected areas. Use your blur tool judiciously, however, or you will blur image details, which is just as problematic as the image noise you're trying to eradicate.
Tip: Don't have any way to control shutter speed on your camera? Check to see whether the camera offers a night-time scene mode. In that mode, the camera automatically uses a slow shutter speed. And on some cameras, you can disable the flash for an even slower shutter.
Shooting long exposures
Somewhere in your camera manual -- probably where the specifications are listed -- you should find information about the range of shutter speeds available to you. The longer your camera allows you to keep the shutter open, the darker the scene that you can photograph successfully.
As with ISO adjustments, you need to consider the following caveats when using a slow shutter speed:
- Most people can't hold a camera still enough to capture an image without blurring at exposures longer than about 1/60 second. On a good day -- one that doesn't involve lots of caffeine, for example -- you may be able to get away with 1/30 second if you lean against a wall or other support while taking the picture. But to ensure the sharpest images, use a tripod or put the camera on a solid surface before you press the shutter button.
- Speaking of pressing the shutter button, take advantage of your camera's self-timer function, if available. The slight press of a finger on the camera can create enough camera shake to blur the image, and using the self-timer enables you to take a hands-free shot. Some cameras can be triggered with a remote-control unit or shutter-release cable as well.
Notice the car lights in the Las Vegas images. In the 1/2-second example, the cars in the centre of the image are waiting at a stoplight; in the one and four second examples, the cars appear as light trails.
Be aware that even if the camera remains perfectly still, any objects moving through the scene will appear blurry in long-exposure images. The longer the exposure, the greater the blur.
Content adapted from Shoot Like a Pro!: Digital Photography Techniques, McGraw-Hill Publishing, and used with permission: CNET Networks © 2007, and McGraw-Hill © 2007.
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