When you are shopping for digital cameras you need to understand how they work in order to choose the one that best suits your needs. The following is a list of features that you need to consider.

• Megapixels and resolution: The light-sensitive sensors that make up the CCD (charge-coupled device) in the camera are referred to as pixels. More pixels means higher resolution for bigger and sharper images. Digicams usually list the dimensions of the images they record in pixels: the Canon S30's 2048x1536 image has 3,145,728 or roughly 3.2 Megapixels. If all you want is to send e-mail pictures, 640x480 is fine. Good 8x10 prints, require a 3 or 4 Megapixel digicam.

• Focal lengths of digital cameras differ from film. The CCD area is smaller than 35mm film, so a 7-21mm zoom may be equivalent to 35205mm in 35mm. Digicams usually list 35mm equivalents.

• Optical zooms use moving lens elements. 2x or 3x optical zooms are typical. I like 3x, in the 35205 range, for nice wide-angle to short-telephoto coverage.

• Digital zoom extends the range of optical zoom only by cropping and consequently reduces resolution. It's useful only if you want low-resolution images for things like e-mail. Optical Zoom is the real deal.

• LCD and viewfinders: LCD screens consume valuable battery power and are tough to see in bright light. You'll use the optical viewfinder to save power and frame pictures in bright light. That said, try to get a bright LCD. You'll use it on the water to check framing and exposure. A waterproof case may partially block the viewfinder especially at the wide angle end of the zoom.