The Mystery Of Sensor Size

*Before we start we must keep in mind that all the sensor size mentioned in this article doesn't mean the package size but actual sensor area.

We know that the sensor size is directly affect the sensibility, S/N ratio and also the dynamic range (of cause this is not the only factor). There are some sensor type like 2/3", 1/2", 1/3", 1/4", 1/4.7", 1/6" are commonly used in digital camera and camcorder.

Since we know those typical size of sensor so what does it means 2/3" for the sensor size? Many people say the sensor size in specification is based on the diagonal. Is it true? sometime is correct but most the time are not true.

Below is typical 2/3" sensor diagram (current diagram doesn't show the actual ratio and size of the sensor in real life)

You can see a typical 2/3" sensor diagonal is 11mm, height is 6.6mm and width is 8.8mm. Do you notice that 11mm < 2/3"(about 16.67mm)? Ok, let's see the table below:

We found that the type of sensor is not related to its diagonal. What happen to those sensor size? Where the 1/3", 2/3" from?

Actually most manufacturers (eg. SONY) define their sensor in this way : (Width + Height) almost equal to sensor type.

here are some examples:

1. 4.8mm (width) + 3.6mm (height) = 0.336" ? 1/3"(0.3") ?8.33mm <> 6mm(diagonal)
2. 6.4mm (width) + 4.8mm (height) = 0.448" ? 1/2"(0.5") ?12.5mm <> 8mm(diagonal)
3. 8.8mm (width) + 6.6mm (height) = 0.616" ? 2/3"(0.7") ?16.67mm <> 11mm(diagonal)