A Simple Rule of Thumb
Buy all the megapixels you can comfortably afford provided you check for picture noise and buy a CCD sensor until newer sensors demonstrate superior performance.
The tradeoffs:
In deciding the number of megapixels you want in a digital camera you need to consider the tradeoffs among detail, noise and cost.
Advantages of More Megapixels
1. More detail is evident when you print the picture
The greater the number of megapixels, the greater the detail. Consider the graph below:
Note that if we considered all possible number of megapixels the line would be a curve. The important thing to note that the amount of detail increases in relationship to the square route of the number of megapixels so that a 4 MP camera gives 41% more detail than a 2 MP camera, not 200%. In looking at 10 x 7.5 pictures you will probably see a noticable increase in detail between a 2 and 3 MP camera, but much less of an increase between 4 and 5 MP.
2. Cropping (cutting extra material to make a smaller picture from a
larger one: made simple by photo editors)
Consider a 3 and a 4 megapixel camera for which you want an 8x10
inch picture of a particular scene. Once you take the two pictures,
you decide you want to remove some defect in
the picture. Cropping 25% of an 11x14 inch, 4 megapixel picture
will result in an 8x10 inch
picture with the
same
amount
of detail as an uncropped 8x10 inch 3 megapixel picture.
3. Cameras with more megapixels can be used to shoot pictures of fewer
megapixels
If you buy a 5 megapixel camera, you can change the setting and
shoot pictures of 1, 2, 3, 4, or 5 megapixels as the situation requires;
generally, you can always shoot pictures with fewer megapixels than
is possible.
However,
no 2 megapixel camera can take pictures of more than 2 megapixels.
Disadvantages of more megapixels
1. Possibility of more noise in pictures.
If a camera firm produces two cameras that differ only by the number of megapixels and the sensor is the same size the camera with more megapixels is likely to have more picture noise than the one with less. The larger the physical dimensions of a sensor for a particular number of megapixels the less noise is likely. Because firms have varying success in reducing noise you need to check the reviews and picture galleries closely.
2. Cost
The more megapixels the greater the cost. An additional megapixel will cost you between $50-100 up to the megapixel frontier where the cost rises sharpely.
Type of Sensor as an
Attribute Is Becoming Almost as Important as Megapixels
Currently, all of the cameras in the price range have CCD
sensors (in which a sensor at a particular location records
one of three colors of light and each sensor has the same
sensitivity
to light). Fuji has a 4th generation SR sensor where the sensors
have two sensitivities to light, giving it better
performance
in scenes where the light varies from bright sunlight to deep
shade. Right
now, the
Fuji 4th generation sensor cameras have received very mixed reviews
so if you are at all cautious you might wait until Fuji makes
improvements in the next round of cameras. Fuji also has a 4th
generation HR sensor with two types of sensors, but Fuji has yet
to overcome the noise problems of
this sensor. Sony has created a sensor that uses four colors
of light; this sensor has yet to be reviewed. Digital SLR cameras
also have more varieties of sensors: Canon uses a CMOS sensor and
Sigma
uses
a
Foveon
sensor
that record three sensitivities of light at the same location,
but neither of these sensors are available in lower-end cameras.
Remember, digital cameras are undergoing rapid technological change
and at
some point
the
CCD
sensor may
be replaced.