With CHDK running, enter Alt mode, and push your camera's Menu button. Navigate to Histogram Parameters, and change it to Show Live Histogram [Always]. Push Menu again, and exit Alt mode. Most cameras let you instantly toggle the live histogram by holding the shutter halfway down and pushing the joystick down.

Now you can track exposure and details while composing a shot. Especially in manual modes, you'll typically want to make the curve spread across the entire graph for perfect exposure. Note that in some situations, such as at night, the curve will still favor one side the the graph.

Take Long-Exposure Photos

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

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.