Have you noticed that many point-and-shoot cameras have as many, or more pixels than a digital SLR (DSLR)?
And, they cost a lot less than a DSLR.
However, point-and-shoot camera don't produce the same quality of photograph as do DSLR cameras.
That's because the photosites on point-and-shoot camera sensors, which collect photons, are smaller than those on DSLR cameras.
They don't collect as many photons as do the larger photosites on DSLR camera sensors.
These smaller photosites have a poor ratio of photons to noise.
This ratio is called the signal-to-noise ratio.
DSLR cameras have better ratios of signal (photons) to noise because their larger photosites collect more photons.
The DSLR photosite collects many more photons, overwhelming the noise.
Let's say the small photosite on a point-and-shoot camera collects 16 photons.
It also generates 4 noise photons (√16 = 4).
|16 photons||4 noise photons|
The signal-to-noise ratio is 4.
Let's say a DSLR photosite collects four times more photons because of it's bigger size.
It collects 64 photons, and generates 8 noise photons (√64 = 8).
Again, the amount of noise is about the same, no matter the size of the photosite.
|64 photons||8 noise photons|
The signal-to-noise ratio is 16, a far better ratio than the point-and-shoot camera's ratio of 4.
A DSLR has a greater number of photons versus noise than does a point-and-shoot.
So, more megapixels may be better.
But, you have to consider the size of the photosites.
Bigger photosites collect more photons.