It seriously depends upon 2 factors:
a
) what type of "digicam" you are buying
b
) what you are going to do with it.
In current technology from 5 to 8MP is the "sweet spot" in terms of having "enough resolution". But things are much, much more complicated than that.
If you buy a digital SLR then I would easily recommend 6 to 8MP, or even higher.
If you buy a "consumer digicam", that is an all-in-one without interchangable lenses, I recommend 4 to 6MP.
Why the difference?
Sensor size.
This is what you have to learn yourself through research because, as usual, the industry does not wish to tell you the dirty laundry so you can buy the "biggest and newest", but not necessarily the "best". In all sensors the only way to increase resolution for the same sensor size
(the most common method
) is to make each pixel physically smaller. The most common sizes for consumer digicams is 1/1.8 and 1/2.5 - 1/2.7
http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm
The "dirty laundry" the industry wants to hide is that as resolution increases, but the sensor's overall dimension stays the same,
noise in the image increases. This is because the smaller pixels on the higher resolution sensor collect less photons per exposure, as their physical surface area decreases. Therefore more electronic effects from amplification and leakage gets shown as the S/N ratio of the sensor goes down in response to receiving less "original signal"
(the light hitting the sensor and making the cell charge change
).
On consumer digicams the sensors are very small to begin with; the companies use these small sensors as their required imaging circle shrinks as well. This means that the entire camera, from the optics on back, shrinks in relation to the size of the sensor. This makes smaller cameras and lowers costs. But in the fight to get those higher-and-higher resolution numbers on the outside of the box, to sell the camera in the first place, they must increase resolution while keeping the sensor size the same. And we get the added noise effect.
To see this example pick any 2 cameras where the first model
(4 to 5MP
) was replaced by a second
(8MP
). The Nikon 5700 was replaced by the 8700, the Panasonic FZ20 was replaced by the FZ30, etc. In all examples of tests
http://www.dpreview.com/
you will find the resolution went up with the new models, but so did the noise level in the photographs - and actually making the very high ISO settings not as useful.
However if you want a consumer camera and wish to
consistently make 8x10 prints then go with the 8MP. If you mostly want smaller than that 5 to 6MP will get, overall, lower noise.
You can always reduce the noise using Noise Ninja with the 8MP if you prefer.
SLR's avoid most of this problem because they must use a much larger sensor due to the fact that they have fitted lenses originally designed for a much larger format
(than current common digital
), 35mm. So the SLR's use an image sensor that is much larger than consumer digicams - APS-C - and thanks to that vastly increased size noise on a digital SLR is fantastically lower to begin with. So they have plenty of room to increase resolution while maintaining good pixel size, and therefore low noise.
. 