Originally posted by Marc Sabatella I am not sure what you are asking. Are you asking if a camera that is advertised as 10MP actually has less than 10MP because of crop factor? Of course not. It's got 10MP, period. The "crop factor" comes from the those pixels are crammed into a an area smaller than a rectangle of 35mm film - it's as if someone took the piece of film and cropped off the edges. But when they say there are 10MP in a camera, that's how many pixels there are.
Could be. You might want to point out the specific paragraph that has you confused. I took a look at the article, and it appears to have not been written by a native English speaker (he's French). As a result, while the technical information is probably correct, it is not expressed as well as it could be.
Anyhow, the actual answer your question is that the "crop factor" *does* affect resolution, but not in the way you seem to be thinking. You have 10MP to work with on a 10MP camera - that much is unquestioned. But because those 10MP are crammed into a smaller area than a piece of film, that means you have to blow the image up more to get a given sized print than you would to create an image from a film camera. The effect is *exactly* like blowing up the image from a 35mm camera to 6x9", then cropping out the edges of the print to yield a 4x6" print. It creates the illusion of having shot with a longer lens, but on that 35mm camera, you'd have gotten better results actually shooting with the longer lens in the first place rather than shooting with the shorter lens and then blowing p the image bigger.
Somehow, I have a feeling the preceding paragraph is going to create more questions than it answers...
This is the part of the article that confused me.
Bingo! Certainly we lose in wide angle, but we gain in long focal lengths, when getting closer to the subject becomes problematic. Yes, but slow down ! We considered here that our two sensors had the same number of pixels, now it is not always (if not rarely) the case. . There are a lot of sensors, APS with 6mp (megapixels), 8mp, 10mp, 12mp, and 35FF 11mp, 12.7mp, 16mp. How and why does it affect crop factor ?
If our 35FF sensor has more pixels than our APS sensor, we could manually crop the image of the 35FF, keeping same number of pixels as our APS. So, we could enlarge our FF shot, still at same printing size. The question which arises then is : how much pixels do we need on our 35FF sensor to crop at 1.6x ratio and still the have same number of pixels as in APS, what shall cancel then the crop factor of the APS. To determine this coefficient, it is enough to think in pixel density. The pixel being a surface, if one want to obtain the same number of pixels once cropped at 1.6x, our FF will have to have 1.6 ² = 2.56 times more pixels than the APS.
Let's take some concrete cases. A 10D is an APS, with 1.6 cropfactor, and 6.3mp. A 5D is 35FF (no or equal to 1 cropfactor), and 12.7mp.
If we crop the 5D like the 10D, we get 12.7 / 1.6 ² = 4.96mp. Our 10D has indeed an advantage, but smaller than its cropfactor of 1.6.
Let's take now an 1DsII of 16.6mp against our 10D. Cropping 1DsII shot like 10D gives us 16.6 / 1.6 ² = 6.5mp ! Same resolution, the advantage in long focal lenghts of the 10D APS on the 1DsII 35FF is thus non-existent !
It appears that the cropfactor alone is not a good indicator, and that it must be moved closer to the pixel density. I thus take the liberty to advance another way of seeing things, by defining a "real magnification factor ".
So be pr the pixel ratio between the number of pixels of the big sensor on that of the small sensor, and cf the cropfactor of the small sensor in regard to the big sensor (here one 35mm). I put down :
rmf = cf / root (pr)
Let us verify it with both quoted cases above : between 10D and 5D, pr = 12.7 / 6.3 = 2.015
10D rmf compared to 5D = cf / root (pr) = 1.6 / root (2.015) = 1.12
10D real magnification factor compared to 5D is so 1.12 !
Between 10D and 1DsII, pr = 16.6 / 6.3 = 2.63. rmf = 1.6 root (2.63) = 0.98 !
Indeed, our 10D, in spite of its 1.6 cropfactor, got a real magnification factor less interesting than 1DsII !