question for the Professional pixel slingers,
if low megapixels is better, why are all the pros shooting extremely high megapixels, and why are the camera makers trying to push the megapixels even higher,.....?
There are some misconceptions in this thread. Higher pixel counts aren't always better -- there are multiple tradeoffs at stake.
The issue is that digital cameras can have vastly different sensor sizes, which directly affects the size of each individual pixel. Pixel size directly influences the ability of the sensor to gather light. What this all means is that the smaller the pixels, the worse the camera does in low light.
Take a look at this image, which compares the most common sensor sizes used in cameras today:
You can ignore the top "medium format" image. Next, in the upper left, is a full frame sensor, which is the same size as a frame of 35mm film. In the old film days, even most point and shoot cameras shot essentially the same size film (though there were a few orphan miniature formats along the way: disc, APS, old 110 & 126, etc.). Today, though, digital point and shoot cameras have very tiny sensors, which which is what makes it possible to make entire cameras so small, and so affordable. The numbers are hard to interpret, since they don't actually refer to the dimensions of the frame -- but take a look at the comparative size. Most compact digitals today are made with a 1/2.5" sensor, which is TINY. Some of the higher end and larger models might have up to a 1/1.7" sensor, which is still significantly smaller than your pinky nail.
When you squeeze 12 megapixels onto a chip that small, each pixel is a very, very tiny little bucket, and it can't gather much light. Each step up in sensor size improves light-gathering ability, though it also means the camera, and its lenses, must be bigger, too.
Most DSLRs made today use an APS-sized sensor (Panasonic and Olympus have an alternative that is smaller, called "four thirds", which is a nice compact alternative). An APS body with a 12mp sensor will outperform a compact with its tiny sensor. A 12mp full frame body will outperform all of them.
Pros don't always shoot very high megapixels. It's true that Canon, Nikon, and Sony all make high resolution (24mp+) full frame bodies, which are great for use in studios and landscape settings where you shoot with artificial light or on a tripod. There are many situations, though, when pro shooters need low light performance -- shooting sports, where you need to keep shutter speeds high to freeze motion, low light performances, etc. A 12mp full frame Nikon D700 (what I shoot), D3, or D3s will, in most circumstances, be better in low light than a 24mp full frame body.
Everything is a compromise, of course.
The current consumer APS SLRs from Nikon, Canon, and Pentax are all quite good. So are the 4/3 bodies from Panasonic and Olympus, which are more compact (they also do mirrorless "micro-4/3" bodies that have the same size sensor, but no mirror reflex housing, to save additional bulk and weight).
In the compact range, the Canon G11 and S90 (same sensor, different bodies) and the Panasonic LX3 are generally considered to give the best image quality in a point and shoot body -- good quality lenses, good electronics, and sensors that aren't overly ambitious.
More here:
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm
