Forword
In the first sensor part, the different technologies were explained (CCD, CMOS et foveon X3). This new technical part focuses more on the relation between the photosite size (photodiode), sensibility (ISOs) and resolution (pixel number).
Sensor size:
While comparing the different reviews and test of the digital cameras (reflex, bridge and compacts), several technical specifications are provided, but the sensor size is certainly the most confusing one. Is a sensor 1/2.7" smaller, larger or of different proportion than a 2/3" ?
A comprehensive and detailed article can be found at DPreview.com. These values originate from the 50' and to the TV tubes. These sensor values are not the aspect ratio, but the outer diameter of the glas envelope tube. There are no mathematical relationship betweem the sensor size and the "real" (physical) size.
Some sizes:
Type: sensor "size" provided by the manufacturer, Diag. : sensor diagonal dimension (mm), Ratio: width/ height ratio, Width: sensor width (mm), height: height of the sensor (mm), Focal leng.: Focal length (x). Focal length equivalent to 35mm in fold changes (PS: digital cameras have smaller sensor than 35mm cameras).
| Type | Some exemples | Ratio | Diag. | Width | Heigth | Focal leng. |
| 1/3.2" | Canon A100/200 | 4/3 | 5.7 | 4.5 | 3.4 | 7.9 |
| 1/3" | Nikon Coolpix 100 | 4/3 | 6 | 4.8 | 3.6 | 7.5 |
| 1/2.7" | Olympus C760 | 4/3 | 6.6 | 5.3 | 4 | 6.8 |
| 1/2" | Nikon Coolpix 950 | 4/3 | 8 | 6.4 | 4.8 | 5.6 |
| 1/1.8" | Canon Powershot S1 IS, Ixus 500 | 4/3 | 8.9 | 7.2 | 5.3 | 5 |
| 2/3" | Leica Digilux 2, Nikon Coolpix 5700 & 8700, Sony F828, Minolta Dimage A1 & A2 | 4/3 | 11 | 8.8 | 6.6 | 4.1 |
| 1" | 4/3 | 16 | 12.8 | 9.6 | 2.8 | |
| 4/3" | Olympus E-10 | 4/3 | 22.5 | 18 | 13.5 | 2 |
| Nikon D2H | 2/3 | 28 | 23.3 | 15.3 | 1.5 | |
| APS | 2/3 | 30.1 | 25.1 | 16.7 | 1.4 | |
| 35 mm | Canon 1Ds, Kodak DCS-Pro | 2/3 | 43.3 | 36 | 24 | 1 |
Resolution
or number of pixels on the sensor
The current trend of the manufacturers is to increase the number of pixel while keeping the sensor size small in order to decrease the manufacturing costs. The successors of the various Nikon Coolpix 5700 and Minolta Dimage 7i/ A1, respectively the Coolpix 8700 and Dimage A2 offer a resolution of 8 megapixels for the same sensor size.
