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