Makten wrote: HelenB wrote:
Don\'t you have to be careful about what you mean by \'same amount of light\'? The 85 mm f/1.2 becomes a true f/0.9 lens, and in terms of image brightness that is what it stays at regardless of format (ignoring transmission losses of course). The f/1.7 approximation only applies to DoF comparisons.
F/0.9 on APS-C equals f/1.2 on FF, both for DOF and collecting of light per time. I really don\'t get why this is so hard to understand and thus comes up every time different formats are compared and discussed.
A sensor with the area X will have to get twice the exposure compared to a sensor with the area 2X, to get the same noise per image height. Forget about ISO. What you want is photons.
You did read exactly what I wrote, didn\'t you? I suggested that one needed to be careful about the nature of the comparison that one was making. I hope that you do not disagree with me about the image brightness statement, or about anything else I wrote. If so, exactly what do you disagree with?
