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Digital Photography Tutorial: Camera Sensors

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The heart of all digital cameras is of course the digital imaging sensor. It is the component that converts the light coming from the subject you are photographing into an electronic signal, and ultimately into the digital photograph that you can view or print.

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The Three Main Sensor Types

Although they all perform the same task and operate in broadly the same way, there are in fact three different types of sensor in common use today. The most popular is the CCD, or Charge Coupled Device, which is found in all types of digital cameras from nearly all manufacturers. CCDs have been around since the 1960s, and have become very advanced, however they can be slower to operate than other types of sensor.

The main alternative to CCD is the CMOS, or Complimentary Metal-Oxide Semiconductor sensor. This is less widely used, the main proponent of this technology being Canon, which uses it in its EOS range of digital SLR cameras. CMOS sensors have some of the signal processing transistors mounted alongside the sensor cell, so they operate more quickly and can be cheaper to make, but may also have lower image quality, although Canon’s top professional SLRs are equipped with them so this is certainly not always the case.

A third but less common type of sensor is the revolutionary Foveon X3, which offers a number of advantages over conventional sensors but is so far only found in Sigma’s range of digital SLRs and its forthcoming DP1 compact camera. I’ll explain the X3 sensor after I’ve explained how the other two types work.

Fujifilm’s SuperCCD system is basically the same as a conventional CCD, but the individual photocells are octagonal in shape, slightly larger, and are arranged in a diagonal honeycomb pattern, rather than the regular rectangular grid layout of other sensors, enabling the cells to be closer together. The SuperCCD SR sensors have two photocells at each point on the sensor, one to record shadow detail and the other for highlights, giving extended dynamic range.

As you can see from this picture, regardless what type they are, all digital sensors look very similar to the naked eye.
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