seven sizes at one scale, with the crop factor computed from the diagonal
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
Crop is the diagonal of the 35 mm frame divided by the diagonal of the sensor. Sizes come from the specifications named in the right-hand column.
A sensor called «Type 1.0-inch» carries an inch in its name and no inch in its silicon: the diagonal of the image area is 15.9 mm, less than two thirds of 25.4. Type 1/2.3 behaves the same way: the nominal inch of the name is 11.0 mm, while the real diagonal is 7.9 mm.
The figure came to sensors from the television camera tubes used until the 1980s. A tube was measured across the outside diameter of its glass envelope, while the picture was built on a target inside it, and the diagonal of that target came out at roughly two thirds of the diameter. The envelopes are gone; the names and the factor stayed.
This is why the fractions cannot be compared with one another. By name, Type 1.0 ought to be exactly 2.3 times the size of Type 1/2.3; by real diagonals it is 2.0 times. Millimetres are what compare, and millimetres are what the specification prints.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 8 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
