Unlock Advanced Features on Your Canon Digital Camera

Take Long-Exposure Photos

Most point-and-shoots lack the controls to let you take long exposures like this 6-second city street shot, but with CHDK on your Canon, you can. (photo credit: Alan Stafford)
Some photos look best with long exposures that your camera may not be able to capture natively. For example, you can shoot images of stars or dark scenes by keeping the shutter open longer, capturing more light. You could even shoot a 30-second exposure of a city at night, turning a car's brake lights into wispy red streaks.

Camera companies rarely allow this level of control in models below the DSLR level, but the CHDK software can unlock these effects on your Canon point-and-shoot. Just be sure to use a tripod in most situations, since the camera has to remain perfectly steady.

Enter Alt mode, push the Menu button, and choose Extra Photo Operations. Pick Override shutter speed. From here, you can set extremely long exposures--or set up shorter exposures than your camera might normally support. Your camera might be physically unable to achieve some of the quickest available speeds, but the longest times should be no problem. Set the Value Factor to 1, push Menu, and leave Alt mode. (To turn the shutter override off, return to this menu and choose Off.) Now your pictures will use a shutter length that you select from a list, rather than relying on the camera to set its own speed automatically.

Automate Advanced Tasks

You can find useful scripts on the CHDK Web site and load them on to your SD Card to automate advanced features on your camera.
CHDK offers an impressive bump to your camera's built-in features, but you can obtain even more options through its scripting language. You save these scripts to the SD Card from a PC, and once installed they can execute several commands--such as exposure bracketing, where the camera automatically captures a series of differently exposed pictures. With that process, for example, you can shoot a series of photos to produce into a stunningly detailed High Dynamic Range scene, all with a single press of the shutter.

One of my favorite scripts sets time-lapse recordings. This tool will automatically fire your camera shutter on an interval that you select. Later, on a PC, you can import the individual photos into a video editor, and create sped-up shots of flowers opening, street traffic, and other progressive scenes.

Scripts are written in a version of BASIC. You can download many of them through the CHDK Web site. Visit this Web page for a time-lapse script, and just copy the BASIC text from the gray box. Paste the text in a plain-text editor, and save the file as 'ult_intervl.bas' in your SD Card's Scripts folder.

Insert the card into your camera, enter Alt mode, push the Menu button, and select Scripting parameters. Choose Load script from file..., navigate to the script, and select it. In the script menu, you can change some of the variables--the 'Script parameters'--to make it ideal for time-lapse photos.

The "delay" settings cause the camera to wait a fixed amount of time until your first shot is taken. I usually leave that off and then set a total number of shots that I would like to record. The "interval" settings are the most important because they govern the pause between photos. For fast-moving scenes, such as a busy sidewalk, I might wait just a few seconds. For slow scenes, such as stars drifting in the sky, I would set it to wait a minute or more.

Set the camera on a tripod or in another stationary position. Push the camera's Menu button, but stay in Alt mode. Push the shutter button to activate the script. When you're finished, leave Alt mode to go back to regular shooting.

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