"When shopping for cameras, I see a listing for effective magapixels. What is an 'effective magapixel'? What are some other things I need to look for in a digital camera?"
- Dave, Wahoo, Nebraska.

What I see when I examine the specifications for cameras advertised with "effective megapixels" seems to be a difference between the physical specifications for the Charge Coupled Device (CCD) and the pixels that actually get used in the image. The CCD is a semiconductor array of light-sensitive devices that convert incoming light into electrical signals that are processed to create the digital image. In most cases, the numbers appear to be related to the actual image resolution being captured.

For example, the HP PhotoSmart 945 shows it as having a 5.0 effective megapixel CCD and its maximum resolution is 2608x1952 pixels (2608 x 1952 = 5,090,816 pixels.) While there are more than 5 million pixels in the captured image, the pixels are rounded down to 5 megapixels.

With all of the camera specifications I examined, the "effective pixel" values almost always appeared to be lower than the physical pixel numbers (decimal), and thus probably provide a more accurate representation relative to the resolution capability of the images taken.

From a long-time film-photography perspective, I look for several things when picking out a new digital camera.

1. Maximum resolution (effective, recording, whatever). Take the time to find out what the maximum image size is that the camera is capable of recording. High resolution images give you more options when it comes to final processing, including cropping, compression, or other image manipulation that discards some of the original data. Higher resolution images are also more desirable for making prints.
   
   
2. Optical vs. Digital zoom. Digital zoom is the electronic version of magnifying your photo. The bottom line here is that you will give up detail to capture only a portion of the image. Why get a 6 megapixel camera only to use 2 or 3 megapixels when you save images?
   
   
3. Storage type and size. All the pictures you take have to be stored somewhere, usually on a flash memory card of a certain capacity. Most cameras will include a starter card of some sort. The number of images you can get on a card will depend on the resolution and complexity of the pictures you take, but work with some average numbers and figure out how big a card you can get for the camera. You should figure on getting several additional memory cards, especially if you will be away from your computer while shooting pictures. I also take into account what type of media is used, and if any adapters to transfer the pictures to my computer are included. Using a USB memory card reader is a lot easier than connecting the camera to the computer to get your pictures.
   
   
4. Batteries. Most cameras can and do use rechargeable batteries, although some early ones required alkaline. Alkaline batteries make camera operation expensive over the life of the camera. No matter what type of batteries it uses, you will want to have spares with you. When they die, you cannot always stop to recharge.
   
   
5. Cost. This is not at the top of my list, but is always a consideration. By cost, I mean not just the cost of the camera, but the cost of additional memory cards and batteries. You may have other cost factors as well, including the need for a new camera bag, filters, strobes, etc. that will probably be just different enough from what you already have to require new purchases. Cost considerations could also overlap into printing, hard drive and optical backup storage, just to name a few.
   
   
6. Interchangeable lenses - also see cost and optical zoom. Lenses are a big add-on cost, but the purpose is to expand on the features without having to resort to multiple camera bodies to do it. The majority of digital cameras do not support interchangeable lenses, and the ones that do are all at the high-end of the price range.

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