This will be my last post on this subject, with the focus being on image quality and the effects of resolution. I think it is easy for us as photographers to want more resolution, but the question is, at what cost? I would rather see camera manufactures spend time improving the dynamic range (the range of light) that the camera can capture. Right now there are many situations where you need to make HDR (High Dynamic Range) photos in order to capture shadow and highlight details. HDR, done right can look very nice, but why should I have to take 3-9 images to capture all that?
Anyway, back to resolution. 12MP on a compact (image size is the same) is denser than 12MP on a crop or full frame sensor DSLR. What? How is that possible? Very easily, the physical size of the sensors themselves are different. Each MP on a compact camera is smaller than the MP on a crop or full frame sensor DSLR, which is why a DSLR offers better image quality. The larger the pixel the more light it can collect, with the result being better image quality. The advantage of a camera with denser pixels is that you might have a little bit more room to crop your images, but the amount is minimal at best. This explains why the 12MP D700 produces crisper, more life like images, than a 12MP compact camera, in all but the most ideal lighting conditions.
So what does that have to do with our photography? Well, the point is, as camera manufactures try to cram more MP into camera bodies they are making the pixels on the sensor smaller, and thus less sensitive to light, which means there are more chances of noise getting in to the image. If I am shooting colour images with the D300 for example, I try to avoid shooting at over ISO800, because the noise starts to interfere with the detail, and thus resolution of the image. The amount of pixels are the same, but the quality of light captured by those pixels at higher sensitivity drops off. This is another reason why larger, less dense pixels are better.
That being said, over time the camera manufactures have found ways to control the noise created by the pixels as they increase in size, but over the last few years we have seen little or no real improvement in crop sensor cameras. Full frame cameras on the other hand, thanks to the large pixels, have seen dramatic improvements in light sensitivity. You just need to look at images from a Nikon D3 or D3s to see why. Of course, having a full frame sensor does not mean you will always have less noise or more sensitivity. What, didn't you just say the opposite was true? Sort of. Look at the Nikon D3X, Sony A850/900, the sensitivity of these 24MP cameras is not as good as the 12MP D3 or D3s, because the pixels are starting to get smaller again, with similar pixel density of a 6MP crop sensor camera.
What am I getting at? At some point, without a major improvement in sensor technology, we'll continue to be stuck with crop sensor, and soon full frame, cameras that cannot get any more sensitive to light without a dramatic increase in noise. Of course if you have used a Nikon D3 or D3s, you might be asking, why would I need any more? I can get decent images at midnight with no moonlight! Well, the answer is simple, sadly not all of us can afford to buy a Nikon D3s! So we look at the options we have in the crop sensor market. Right now, the Canon 7D and T2i are looking nice, but not really much better than the cameras that came before them. I still wouldn't want to shoot at ISO sensitivities above 800 for images I wanted to print at sizes larger than 4x6, or 8x10 if I used some third party noise reduction software.
So the point is, sure we are getting more resolution out of our cameras, but are they really improving the quality of our images at higher ISO sensitives? For crop sensor cameras, at the moment I would have to say no. At base ISO sensitives we may see an improvement in detail, but at what cost? Oh yeah, I think I already talked about that at the start! I think that is all I have to say about this topic.