We regularly receive emails from readers confused as to the actual size of sensor used in digital cameras. Sensors (CCD / CMOS) are often refered to with an imperial fraction designation such as 1/1.8" or 2/3", this measurement actually originates back in the 1950's and the time of Vidicon tubes. Those who find the specification sheets for these sensors are then even more confused about the relationship between the fraction and the actual diagonal size of the sensor. Inside you'll find an explanation and a table of common sensor sizes. We'll be adding this information to our glossary for future reference.

#### It all started way back when...

The 'Type' designation given to toady's CCD sensors is that it harks back to a set of standard sizes given to TV camera tubes in the 50's. These sizes were typically 1/2", 2/3" etc. The size designation does not define the diagonal of the sensor area but rather the outer diameter of the long glass envelope of the tube. Engineers soon discovered that for various reasons the usable area of this imaging plane was approximately two thirds of the designated size. This designation has clearly stuck (although it should have been thrown out long ago). There appears to be no specific mathematical relationship between the diameter of the imaging circle and the sensor size, although it is always roughly two thirds.

(Diagram shown to scale but much larger than in real life)

#### Common Image Sensor Sizes

Table keywords: "Type" refers to the commonly used type designation for sensors, "Aspect Ratio" refers to the ratio of width to height, "Dia." refers to the diameter of the tube size (this is simply the type covertered to millimeters), "Diagonal / Width / Height" are the dimensions of the sensors image producing area.

 Sensor (mm) Type Aspect Ratio Dia. (mm) Diagonal Width Height 1/3.6" 4:3 7.056 5.000 4.000 3.000 1/3.2" 4:3 7.938 5.680 4.536 3.416 1/3" 4:3 8.467 6.000 4.800 3.600 1/2.7" 4:3 9.407 6.592 5.270 3.960 1/2" 4:3 12.700 8.000 6.400 4.800 1/1.8" 4:3 14.111 8.933 7.176 5.319 2/3" 4:3 16.933 11.000 8.800 6.600 1" 4:3 25.400 16.000 12.800 9.600 4/3" 4:3 33.867 22.500 18.000 13.500 APS-C 3:2 n/a 30.100 25.100 16.700 35 mm 3:2 n/a 43.300 36.000 24.000 645 4:3 n/a 69.700 56.000 41.500

#### Implementation examples

Below is a list of a few digital cameras (as examples) and their sensor size.

 Camera Sensor Type Pixel count Sensor size Canon PowerShot A100 1/3.2" CCD 1.3 million 4.5 x 3.4 mm Canon PowerShot A200 1/3.2" CCD 2.1 million 4.5 x 3.4 mm Casio QV-8000SX 1/3" CCD 1.3 million 4.8 x 3.6 mm Minolta DiMAGE X 1/2.7" CCD 2.1 million 5.3 x 4.0 mm Minolta DiMAGE Xi 1/2.7" CCD 3.3 million 5.3 x 4.0 mm Nikon Coolpix 950 1/2" CCD 2.1 million 6.4 x 4.8 mm Nikon Coolpix 995 1/1.8" CCD 3.3 million 7.2 x 5.3 mm Nikon Coolpix 4500 1/1.8" CCD 4.1 million 7.2 x 5.3 mm Olympus C-5050 Zoom 1/1.8" CCD 5.2 million 7.2 x 5.3 mm Sony DSC-F717 2/3" CCD 5.2 million 8.8 x 6.6 mm Minolta DiMAGE 7Hi 2/3" CCD 5.2 million 8.8 x 6.6 mm Canon EOS-D30 CMOS 3.2 million 22.7 x 15.1 mm Nikon D1 CCD 2.7 million 23.7 x 15.6 mm Nikon D100 CCD 6.3 million 23.7 x 15.6 mm Canon EOS-1Ds CMOS 11.4 million 36 x 24 mm Kodak DSC-14n CMOS 13.8 million 36 x 24 mm