Having played with both a Pentax KP (24Mp APSC) and a K1(36Mp Full Frame) I was surprised to find that at high ISO (6400+) I was getting significantly better images out of the crop sensor. Having read numerous times that full frame sensors got more light than crop sensors I got to thinking what on earth was going on. The basis of the observation was two images shot with KP 35mm f4 and K1 50mm f4 . I assumed that any lens (ignoring loss in the glass) should transmit the same amount of light towards the sensor if at the same f stop as another. Given a 1.5x crop factor there is 2.25x less surface area on a crop sensor so we only get roughly half the light collected by the 35mm as the rest is effectively wasted. Any sensor pixel should be sensitive to the total amount of light falling on it. Given the two cameras mentioned and an arbitrary amount of light X the light per pixel in the crop and full frame should follow as X/2.25 x 1/24,000 and X * 1/36,000. Thus per pixel the full frame gets 48/36 times as much light. Now log to the base two of that is 0.41 which would be the number of stops difference of light exposure. Firstly can someone confirm that my sums are correct. If they are then why on earth is there such a hype about full frame, the amount of extra light here is negligible. Furthermore it appears that the sensor in the KP is a bit newer and a lot better (perhaps some fancy processing too) at handling low light. So why did I want the K1..........both are great cameras I have to say...but you would have expected the opposite observation.