Digital Camera Sensors

Image sensors are the heart of the digital camera, if comparing to a film camera the image sensor is the equivalent to the film.
When purchasing a camera the sales person will most likely try to sell a camera based on the number of Megapixels in the cameras sensor, but this is only part of the story. A more important issue is how large is the sensor and how large are the pixels on the sensor.

Image sensors are the heart of the digital camera, if comparing to a film camera the image sensor is the equivalent to the film.

Sensor Size and MegaPixels

When purchasing a camera the sales person will most likely try to sell a camera based on the number of Megapixels in the cameras sensor, but this is only part of the story. A more important issue is how large is the sensor and how large are the pixels on the sensor.

Digital sensors are manufactured and caregorized in various sizes, summarised as follows:

Sensor Type
Sensor Width
Sensor Height
Inch
mm
mm
1/3.6
4.00
3.00
1/3.2
4.54
3.42
1/3
4.8
3.6
1/2.7
5.37
4.03
1/2.5
5.76
4.29
1/2
6.40
4.80
1/1.8
7.18
5.32
1/1.7
7.6
5.70
2/3
8.80
6.60
1.0
12.80
9.60
4/3
18.00
13.50
Nikon APS-C
23.6
15.8
Nikon 35mm
36.0
23.90

Because of the many different sensor sizes used, the size of each pixel detecting the light arriving at the sensor will vary.

Some approximate examples of pixel sizes for different sizes of sensors are given as follows:

35mm Full Size Sensor
8.45 Microns
NikonAPS-C Sensor
5.40 Microns
Typical Compact Camera
1-2 Microns

Basic theory of light detection, determines that the larger the pixel, the better will be the signal to noise ratio, hence better image quality in respect to noise and the smaller the sensor size the poorer the noise performance will be.

The effect of noise on the image is such that a noisy or speckled effect will become more obvious as the ISO of the camera is increased at lower light levels.

An important criteria for the camera purchaser is that the larger the sensor, the more expensive the camera will be.

MegaPixels and Print Size

The number of megapixels in the sensor effectively determine the maximum print size you can get, but still retain sharpness in the final print. For most practical purposes the figures below will vary depending on the sharpness of the image, camera shake and how the image is prepared prior to printing. The maximum size print that can be obtained from various size sensors, assuming an aspect ratio of 1.5 which is the case for most sensors can be assumed to approximate the figures given below.

Sensor Size
Print Size
Print Size
MPixel
Inches
mm
4
16.3×10.8
414×276
6
20.0×13.3
508×338
8
23.0×15.4
586×391
10
25.8×17.2
655×437
12
28.1×18.7
714×475
14
30.5×20.4
776×517
16
32.7×21.8
830×553
18
34.6×23.1
880×587
20
36.5×24.3
927×618

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