Digital Camera Sensors
The sensor in a digital camera is one the most important parts and yet there is little information about them. Sensors are described using a standard developed in the 1950s for Vidicon tubes which were used in tv cameras. It seems that manufacturers have deliberately used this system to obscure the fact that sensors are very small.
| The size of the sensor does make a major difference to image quality. Many more megapixels are packed into a small sensor, it makes it harder for each individual photosite to keep its electrical charge so noise occurs. This is one of the main reasons DSLR cameras have far better performance at high ISO speeds when compared to a compact camera.There are advantages in having having a small sensor, it would be impossible to make one of the long 28-500mm zoom lens cameras with a larger sensor. But as far as image quality is concerned bigger is definitely better. |
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The illustration above gives an idea of the different sizes of sensor. Many compact cameras will have a 1/2.5" sensor, it's obvious how much larger the APS-C sensor found in a DSLR is.
Here is a simplified version of how a sensor in a digital camera works. After the light goes into the lens it passes through colour filters that separate the light into red, green and blue components that make up a colour image. The charge the pixel holds is in proportion to how much light fell on it. The electric pulse is then amplified by an analog to digital converter and finally processed to give a digital image. There are two types of sensor, CCD and CMOS they both work in a similar way. |
| Image Sensor |
Width
|
Height
|
Diagonal |
| 1/2.7" | 5.4mm | 4.0mm |
6.7mm |
| 1/2.5" | 5.8mm | 4.3mm |
7.2mm
|
| 1/1.8" | 7.2mm | 5.3mm |
8.9mm |
| 1/1.7" | 7.6mm | 5.7mm | 9.5mm |
| 4/3rds | 18mm | 13.5mm | 22.5mm |
|
APS-C
|
23.7mm | 15.6mm | 28.4mm |
| 35mm | 36.0mm | 24.0mm | 43.3mm |
| This table gives the sizes of a range of different sensors. A normal focal length for the sensor size is is approximately the figure given in the diagonal column. The perspective we see with our eyes is considered to be the standard focal length for a lens. |
Below are listed a range of current cameras with their sensor sizes: |
| Nikon P5100 |
12 megapixels |
1/1.7" |
| Sony Cyber-shot DSC-T70 | 8 megapixels |
1/2.5" |
| Olympus FE290 | 7 megapixels |
1/2.5" |
| Sony Alpha A350 | 14 megapixels |
APS-C |
| Canon EOS 450D |
12 megapixels | APS-C |
| Olympus mju 790 SW | 7 megapixels | 1/2.3" |
| Canon IXUS 860IS | 8 megapixels | 1/2.5" |
| Olympus E-420 | 10 megapixels |
4/3rds |
| Canon EOS-1Ds Mark III | 21 megapixels |
35mm |