>Forgive my posting this where it doesn't really belong, but I >can't find a more suitable location - anyway I do at least own >200 and 300s bodies! > >I can't understand what exactly is meant when sensor sizes are >quoted as (say) 1/2.55 inch. Does this mean one dimension is >0.392 inch? In which case, which dimension is it, the short, >the long, or the diagonal? > >I just saw a Sony camera sensor described at 1/3.91 inch. How >opaque can they get? I would be greatful if anyone can confirm >to me that these measurements are indeed reciprocals, and in >this case the Sony sensor is 0.2556 inch or 6.5mm in some >unspecified dimension! > >Mnay thanks for any guidance.
The 1/2.55 dimensions are archaic, and I have no idea why they keep on going in this era. It's a reference to the outer diameter of a video camera tube, so it doesn't directly relate to anything about the digital camera it describes. So that 1/3.91 Sensor refers to a tube of 6.5mm outside diameter, so the sensr itself must be a little smaller, maybe 6mm diagonal. See Wikipedia
Should read en.wikipedia.org/wiki/Image_sensor_format, but the "form" gets lost somewhere.