Inside all digital cameras can be found an important device called a sensor, it’s function is to capture the image you have photographed, think of it like the film in a 35mm camera except that it does the process digitally and never needs replacing.
The sensor captures the image by having a surface covered in millions of light sensitive picture gathering elements called pixels, one million of which are known as a Megapixel (1 Mp), hence a digital camera with a rating of 6 Mp has a sensor with 6 million pixels on it’s surface.
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It’s commonly believed that sensors with the same Megapixel rating for example lets say 10Mp are the same in any camera rated at 10Mp with an identical size and operation, in fact this is not the case as sensors do vary in physical size and also in the way they actually capture the image. |
You will find several types of sensor fitted to digital cameras, the most common being the CCD (Charged Couple Device) but there is also the CMOS (Complementary Metal-Oxide Semiconductor) favoured by Canon for their D-SLR’s, and in Sigma cameras you will find the somewhat different Foveon X3 sensor.
All you really need to know about the different types of sensor is that they all produce excellent results and it is unnecessary to base your choice of camera on the type of sensor fitted to a particular model.
If the type of sensor isn’t to important then we have to ask ourselves “Does the Size Matter”? Now calm down ladies, I thought that might get your attention but I am afraid we are still talking about the physical size of sensors, and yes size does matter.
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Have a look at this size comparison chart above, which although not to scale will give you an idea of how varied the sensor sizes are. We have used the white outer line to represent the size of a 35mm negative (36mm x 24mm), and if a digital sensor is of this size it is known as “Full Frame”.
The orange line in the chart represents the average size of an APS-C sized sensor, which is the most common size found in D-SLR cameras, the blue line is the 4/3˝ sensor favoured by Olympus and Panasonic, this is the smallest sensor you will find in a D-SLR camera. All of the other smaller sized sensors shown on the comparison chart are all to be found in bridge and compact cameras.
Now if you are trying to work out how a sensor size let’s say 2/3˝ relates to the physical measurement of the sensor don’t bother because it doesn’t, you won’t believe what I am going to tell you next, but after doing some research I found that these designations date back to the 1950’s and relate somehow to TV camera tubes? And yes I don’t understand it either.
But if you look at the table bellow you will find out the true size of the sensors compared to their designations: -
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Size Designation |
Camera Type |
Width in mm |
Height in mm |
|
1/3˝ |
Compact |
4.8 |
3.6 |
|
1/2˝ |
Compact |
6.4 |
4.8 |
|
2/3˝ |
Compact |
8.8 |
6.6 |
|
4/3˝ |
D-SLR |
18.0 |
13.5 |
|
APS-C (Av’ size) |
D-SLR |
25.1 |
16.7 |
|
35mm & Full Frame |
D-SLR |
36.0 |
24.0 |
Why is the size of the sensor important? To answer this question we have to look at how the sensor captures the image. If you remember we mentioned earlier in this article that the surface of a digital sensor is covered in millions of light sensitive picture gathering elements called pixels.
Each individual pixel captures one element of the picture, hence the name pixel (Picture = Pix and el = element). A simple way to think of how the sensor works is to imagine the pixels as microscopic cups on the sensors surface and when the shutter of the camera opens the cups fill up with the light reflecting from your image.
When the shutter closes the amount of light in each cup is converted into an electrical charge (electrons) the sensor then reads the amount of charge in each cup and then coverts it into a voltage that can be interpreted into a digital image.
Now we have a basic idea of how the sensor works we can as a comparison take a large APS-C sensor and a small 1/2˝ sensor both rated at 6 million pixels, what now becomes evident is that as both of these sensors have identical Megapixel ratings then the pixels (cups) have to be much smaller on the 1/2˝ sensor than those on the larger APS-C sensor.
As you will imagine the much smaller pixels (cups) of the 1/2˝ sensor will fill up with the light from the image much quicker than those on a larger sensor, the light can then spill over into neighbouring pixels causing problems such as “Noise” (grainy images) and “Fringing” (coloured halos around the details in your image) that can affect the image quality produced by these small sensors.
I think it is worth mentioning that the image quality from Compact cameras with small sensors these days is gererally very good, and with all of the major camera manufacturers constantly striving to improve image quality, we have to say that with new advances in technology and at low ISO settings they are mostly succeeding, up to a point.
What however is very clear is that a D-SLR camera with a large sensor will always be able to beat a Compact camera (with a smaller sensor) for overall image quality, as whatever new technology is used to improve the output from the smaller sensors can also be used with the already superior larger sensors, always keeping them one step ahead.