On the way home just now, I finally figured out how to explain to the digital shooter the difference camera sensor size makes in photography.
Pizzas usually come in three sizes here in Malaysia: personal, regular and large. A personal pizza is usually divided into four pieces, regular into six, and large into eight. Of course a personal pizza can be divided into eight pieces also, but each of those pieces would be smaller than one-eighth of a large pizza.
Camera sensors are like pizzas. Full-frame digital SLRs like the Canon 1Ds Mk II, 1Ds Mk III and 5D, and the Nikon D3, D3x and D700, have a sensor measuring 36mm x 24mm, which is the size of conventional 35mm film.
Almost every other DSLR has a sensor slightly less than half full-frame. See what Ken Rockwell says here. Olympus SLRs have sensors which are only a quarter full-frame.
As you might expect, the sensors in compact digital cameras are even smaller.
Now about megapixels. Megapixels are like the pieces of a pizza. Sensors are divided into photosensitive sites called pixels. So for any given sensor, the more pixels it has, the smaller each pixel is.
The makers of digital SLRs and compacts like to brag about the increase in megapixels, and fortunately for them, what people don't understand is that it is pointless to have 14 megapixels in a digital compact camera. It is like cutting a personal pizza up into 40 pieces, and expecting it to be able to feed 40 people.
Just as a small piece of pizza is not worth much, so small pixels aren't very useful. They require more light to work effectively (hence reducing low-light performance), and they are more prone to noise.
An initial increase in megapixels is good. However, every sensor has what might be termed an 'optimum pixel count'. It is hard to empirically establish what this value might be, but for a compact digicam it is about 7 megapixels, tops. One must also remember that a compact digicam can still function with 700 megapixels, but only when the lighting is really, really good. The slightest shade would produce a ridiculous amount of noise.
So this 'optimum pixel count' is what might be expressed as the best balance between quality and performance.
Nikon's D2H only had 4 megapixels but retailed at RM13,000. It was a hit with sports photographers because the resolution was sufficient for newspaper prints (no one believes it these days, but 4 megapixels is more than enough for many applications, provided the sensor is good). Only at a low megapixel count can a camera truly function at great speeds for demanding shooting like sports.
Among other popular innovations are 'smile detection' and 'face detection' functions. Smile detection triggers the shutter when the subject smiles, though I cannot imagine how it is supposed to function when taking a group photograph. Does everyone have to smile before the camera snaps away?
As for face detection, it is supposed to render all faces in focus. This is an easy way out for people who don't understand depth-of-field and the significance of a smaller aperture. Then again, today's automatised photographic milieu has done away with the need for any photographic knowledge. One just 'points' and 'shoots'.
Ken Rockwell opines, and I especially agree on this point, that cameras these days are fitted with all kinds of smart functions, ornaments and other paraphernalia, but there has been very little true innovation in making cameras more powerful tools for photography.