Digital camera sensor sizes – selling elastic bands by the metre

When a sensor is advertised/sold as 1/2.3″ most people would think that is the diagonal of the sensor. Well it is NOT! It might even vary drastically between manufacturers.

For historical reasons the diameter of a fictitious Vidicon tube with the same active area is what is advertised!!

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From  http://www.dpreview.com/news/0210/02100402sensorsizes.asp

Unfortunately, it is even more confusing than that…

The same article also has a table, that I have expanded with two ratio columns. Some intermediate rows also added (data via wiki).
(And removed some columns to make it less confusing)

Sensor Asp Width Hight x*Full Factor adver. to real diag.
1/3.6″ 4:3 4.000 3.000 1/72.0 0.71
1/3.2″ 4:3 4.536 3.416 1/55.8 0.72
1/3″ 4:3 4.800 3.600 1/50.0 0.71
1/2.7″ 4:3 5.270 3.960 1/41.4 0.70
1/2.5″ 4:3 5.760 4.290 1/35.0 0.71
1/2.3″ 4:3 6.160 4.620 1/30.4 0.70
1/2″ 4:3 6.400 4.800 1/28.1 0.63
1/1.8″ 4:3 7.176 5.319 1/22.6 0.63
1/1.7″ 4:3 7.600 5.700 1/19.9 0.64
1/1.6″ 4:3 8.080 6.010 1/17.6 0.63
1/1.5″ 4:3 8.800 6.600 1/14.9 0.65
1/1.2″ 4:3 11.000 8.250 1/9.53 0.65
CX 3:2 13.200 8.800 1/7.44
1″ 4:3 12.800 9.600 1/7.03 0.63
μ4/3 4:3 17.300 13.000 1/3.84
4/3″ 4:3 18.000 13.500 1/3.56 0.66
APS-C 3:2 25.100 16.700 1/2.06
APS-H 13:9 29.200 20.200 1/1.46
35 mm 3:2 36.000 24.000 1.000
645 4:3 56.000 41.500 2.690

Note that the actual sensor diagonal is approximately 2/3 (63% -72%) of the advertising figures!!

A 1/2 “sensor is thus effectively only about 1/3″ or 8mm

But to add to the confusion factors vary between models and manufacturers!

Examples

Manufacturer / Model Adver. Width(mm) Height(mm) Real Diag.(mm) Factor adver. to real diag
FujiFilm / F50,60,100,200 1/1.6″ 8 6 10 0.63
FujiFilm / F30, 31 1/1.7″ 7.44 5.58 9.3 0.62
FujiFilm / F900 1/2″ 6.40 4.80 8.00 0.63
Sony /RX100 1″ 13.2 8.8 15.9 0.63
Sony / IMX220 1/2.3″ 6.30 4.72 7.87 0,71

So Sony’s sensor called 1/2.3″ is only 1.6% less in diagonal than what FujiFilm call 1/2″ !!!
Said otherwise Fuji could call Sony’s sensor a 1/2.03″, OR Sony could call Fuji’s 1/2.26″

So be REALLY careful when comparing sensor sizes that you look at the actual area in use!! – if you can get the correct info from the manufacturer!!!

As the factor used can vary with as much as 14% (matching 30% in area) it is easy to make wrong assumptions, and many sites do, assuming that e.g. all sensors called 1/2.3″ has the same actual size. There are NO reason to assume that – unfortunately…

See also this post on the Megapixel craze