Marketers would have us believe that camera performance is tied only to the number of megapixels the sensor has (especially in the case of point-and-shoot cameras). We are lead to believe that there is a direct correlation between megapixels and performance. However, this is not the case.
In order to keep costs low and keep modularity high (as is especially the case with DSLR), overall sensor size rarely changes. For example, ALL ASP-C cameras have 23.6x15.7mm sensor, regardless of what model it is. (I realize that this dimension varies slightly manufacturer to manufacturer but for the most part, each company will stick with one dimension that works for it.) The sensor size doesn't change with an increase in megapixels. (In fact, today's point-and-shoot cameras are getting ever small sensor sizes. The reason is because 'thin is in' and in order for all of your various physical laws to line up [hyperfocal distance, aberation balancing, airy disk, etc.] the thinner the camera, the smaller the sensor has to be. Another advantage to smaller sensor size is lower cost.)
Example: The Canon 40D, 400D, 30D, 450D, 20D, 350D, 300D, 10D, D60 and D30 all have the same sensor SIZE although they have different numbers of PIXELS.
The only way for camera manufacturers to increase megapixels while keeping the sensor size the same (or smaller) is to decrease the physical size of each pixel on the sensor. For example, consider a pixel size of 5.6 micron on an APS-C sensor. That would give you about 11.8 megapixel camera. Let's compare that to a pixel size of 5.1 micron also on an APS-C sensor. That would give a 14.2 megapixel camera. Are those extra megapixels worth it?
Some quick calculations reveal the following.
Effects of shrinking pixels from 5.6 micron to 5.1 micron:
Light sensitivity -17%
Quantum Efficiency -2%
Saturation Level -17%
Dynamic range -1.6dB
Signal-to-noise ratio -1.8dB
Pixel Nonuniformity -19%
As you can see, if you have the same sensor size (and again, digital camera makers usually stick with the same standard sensor size for many, many years) and go for the higher megapixel, you will see a substantial decrease in sensor performance.
Of course, at the same time megapixels are increasing, the technology used to build silicon sensors is also improving. So while pixels are getting smaller, in general manufacturers are able to use newer techniques to reduce noise, increase quantum efficiency, etc. However, given two sensors of the same size and made at around the same time, the lower megapixel camera will work better as long as you don't need to make poster size prints.
Conclusion: Carefully consider the number of megapixels you NEED and don't shell out extra dough ONLY to get more megapixels because you think your camera performance will increase substantially. Hint: You only NEED a huge number of megapixels if you're in the business of making poster size prints.
In order to keep costs low and keep modularity high (as is especially the case with DSLR), overall sensor size rarely changes. For example, ALL ASP-C cameras have 23.6x15.7mm sensor, regardless of what model it is. (I realize that this dimension varies slightly manufacturer to manufacturer but for the most part, each company will stick with one dimension that works for it.) The sensor size doesn't change with an increase in megapixels. (In fact, today's point-and-shoot cameras are getting ever small sensor sizes. The reason is because 'thin is in' and in order for all of your various physical laws to line up [hyperfocal distance, aberation balancing, airy disk, etc.] the thinner the camera, the smaller the sensor has to be. Another advantage to smaller sensor size is lower cost.)
Example: The Canon 40D, 400D, 30D, 450D, 20D, 350D, 300D, 10D, D60 and D30 all have the same sensor SIZE although they have different numbers of PIXELS.
The only way for camera manufacturers to increase megapixels while keeping the sensor size the same (or smaller) is to decrease the physical size of each pixel on the sensor. For example, consider a pixel size of 5.6 micron on an APS-C sensor. That would give you about 11.8 megapixel camera. Let's compare that to a pixel size of 5.1 micron also on an APS-C sensor. That would give a 14.2 megapixel camera. Are those extra megapixels worth it?
Some quick calculations reveal the following.
Effects of shrinking pixels from 5.6 micron to 5.1 micron:
Light sensitivity -17%
Quantum Efficiency -2%
Saturation Level -17%
Dynamic range -1.6dB
Signal-to-noise ratio -1.8dB
Pixel Nonuniformity -19%
As you can see, if you have the same sensor size (and again, digital camera makers usually stick with the same standard sensor size for many, many years) and go for the higher megapixel, you will see a substantial decrease in sensor performance.
Of course, at the same time megapixels are increasing, the technology used to build silicon sensors is also improving. So while pixels are getting smaller, in general manufacturers are able to use newer techniques to reduce noise, increase quantum efficiency, etc. However, given two sensors of the same size and made at around the same time, the lower megapixel camera will work better as long as you don't need to make poster size prints.
Conclusion: Carefully consider the number of megapixels you NEED and don't shell out extra dough ONLY to get more megapixels because you think your camera performance will increase substantially. Hint: You only NEED a huge number of megapixels if you're in the business of making poster size prints.
