While the number of megapixels a camera has is important to image quality, it isn’t the only factor. The other thing that plays a very important role is sensor size. Here, Larry Becker gives a brief intro to digital camera sensor sizes, megapixel counts, and crop factor:
Even if two cameras come out in the same year and have the same megapixel count, that doesn’t make them equal. If one is a full frame sensor and the other is, say, 1/1.7″, then the full frame sensor is the winner, as it will capture remarkably better image detail.
Camera Sensor Size Comparison
Note: These are the main sensor sizes, but of course there are more—like medium format.
Full Frame Sensors: around the same size as a 35mm film negative; found in pro DSLRs and a few high-end mirrorless cameras
APS-C Sensors: have less than half the surface area of a full frame sensor; found in entry level and enthusiast DSLRs, as well as many mirrorless cameras
4/3 Sensors: are a bit smaller than APS-C; found in Panasonic and Olympus mirrorless cameras, plus a few others
Nikon 1 Sensors: just over half the surface area of a 4/3rds sensor; found in Nikon 1 series mirrorless cameras.
2/3 Sensors: even smaller; found in most Fujifilm point and shoots (Fujifilm mirrorless cameras have larger APS-C sensors).
1/1.7″ and 1/2.3″ Sensors: found in point and shoots
And cell phone sensors are even smaller than that!
Another thing sensor size affects is the field of view. If you have a removable lens and you’re looking at the millimeter number on it to figure out what your field of view is going to be, you’ll need to know your camera’s crop factor, which is based on the sensor size. Read more about crop factor here.