A Simple Way to Describe Sensor Size - Diagonal Dimension

Impressionist Painting Effect
FZ1000  Subject 1.3 kilometers from the camera over ocean and beach, I-Zoom at E800mm. Strong atmospheric distortion.

 

In the good old days  of film there were not many sizes from which to choose. Most people used 35mm film which was actually 35mm wide,  and I suspect many would  have been only vaguely aware that any other  size existed.

However since the beginning  of digital photography there has been a profusion and confusion of sensor sizes. Adding to the muddle, camera makers got into the habit of naming their sensor sizes in the most bizarre way. They used as reference the diameter of a notional cathode ray tube which would have been required in the 1950's to incorporate the particular sensor. To make matters worse they described this in inches then expressed the dimension in a weird inverted fashion like [1/1.7 inches].  Nobody presented with this bit of nonsense would have the faintest  clue how large the sensor might actually be.  

Maybe the manufacturers were deliberately obfuscating the size issue, perhaps to divert consumer's attention from the fact that most digital cameras used a sensor very much smaller than the imaging area given by 35mm film.

There is a simple, useful alternative  namely to designate a sensor by it's diagonal dimension. Lets' see how this works in the table below:

Sensor Type	Aspect Ratio	Nominal Dimensions (mm)	Diagonal (mm)	Area (squ.mm)	Focal length Factor
Medium Format	Various	Various, about 44x33	Various about 55	Various about 1452	Various about 0.78
Full Frame	3:2	36x24	43	864	1.0
APS-C Sony et al	3:2	23.5x15.6	28	367	1.5
APS-C Canon	3:2	22.3x14.9	27	332	1.6
Four Thirds, Micro 4/3	4:3	17.3x13	21.6	225	2.0
One inch	3:2	13.2x8.8	15.9	116	2.7
2/3"	4:3	8.8x6.6	11	58	3.9
1/1.7"	4:3	Various about 7.5x5.6	Various about 9.3	Various about 42	4.6
1.2"	4:3	6.4x4.8	8	30	5.4
1/2.3"	4:3	6.1x4.6	7.7	28	5.6

 

So, instead of calling  the sensor in the Panasonic FZ1000 and several other cameras,  "one inch" which means nothing it can be described by the diagonal which is 15.9mm which is at least something real and useful for those consumers who might want to know the size of the sensor in their camera.

I really don't know  why this simple naming system has not become universal, it seems so completely obvious to me. Not to others apparently.