Master your DSLR: Image sensors
HOW DOES YOUR CAMERA TURN LIGHT THAT’S PIPED THROUGH THE LENS INTO A DIGITAL IMAGE?
WHILE AUTOFOCUS ACCURACY and speed, continuous shooting rate, buffer size and build quality are all important considerations when choosing a camera, it’s actually the performance of the camera’s imaging sensor that really matters most.
How the sensor responds to the light collected by the lens is key to the quality of your photographs, with the degree of detail the sensor is capable of resolving, the range of brightness it can record and the amount of noise that’s created laying the foundations for the final, processed image.
Your camera’s sensor is made up of millions of individual light-sensitive photosites, commonly referred to as pixels. These can be minute — a fraction of the width of a human hair in size — and each one generates a distinct electrical signal in response to the luminance or brightness of the light that it’s exposed to. The more pixels that a sensor has, the higher its resolution. Images recorded in a higher resolution will be larger, able to hold more fine detail and allow you to crop the picture to change the composition or enlarge an object while still retaining a usable image size. But cramming more pixels onto a sensor can have a detrimental effect on image quality too. It’s all down to the sensor’s size and the signal-to-noise ratio.
On a camera with a small high-resolution sensor, the photosites will be smaller and more densely packed together. As a result, they capture less light compared with the amount of noise or interference recorded. Larger sensors enable the use of larger photosites, which capture more light. As a result, the signal-to-noise ratio is higher. This is why the pictures produced by a high-res smartphone camera will look worse, particularly in low light, than those captured by a SLR that shares the same pixel count.
In addition to capturing more light and having the potential to produce a ‘cleaner’ image at higher ISOs, larger sensors affect your pictures in other ways. In general, the larger the sensor, the more likely the image will be rendered with greater fine detail, smoother colours and a broader range of tones. Larger sensors also make it easier to achieve a tighter depth of field, too.
The type of sensor has an impact too. CCD (charge-coupled device) sensors used to be the preferred choice for their dynamic range and handling of noise, but these days, most camera sensors use CMOS (complementary metal-oxide-semiconductor) technology. CMOS requires less power to operate, so is well-suited to the fast burst speeds required of sporty SLRs.