First of all, let’s break down what an image sensor actually is: an electronic device that translates an optical image to an electrical signal. The sensor receives the light coming in via the lens into the camera, and then turns that into an image. The individual pixels on the sensor are light-sensitive elements which record the light that hits them. This is a very simplified version of how an image sensor works - there are many other elements, for example the camera’s processor, that play a part in image creation.
Image sensors come in a range of sizes, and the specific size can affect the image quality of photos. Looking at the different sizes available, some people incorrectly assume that if you’re using a camera with a smaller sensor, the subject or scene you’re trying to capture is reduced.
For example, if you’re taking a landscape photo of Tower Bridge, the assumption is that you’ll include more of the bridge in the shot if you’re using a full-frame camera than a camera with a smaller sensor. But this is not the case. The size is relative only to the amount of light the camera captures.
Of all the camera types, DSLRs have the largest sensor size and, typically, better image quality. While a compact or bridge camera may have a similar megapixel (Mp) rating, the sensor is smaller, and it can’t let in the same amount of light.
If you place a mug and a bucket out in the rain, the bucket would catch more water, and an image sensor works on the same principle. The bigger the sensor, the more light it lets in.
Digital cameras primarily use two different types of sensor: CMOS and CCD. Each type uses different technology for capturing images digitally, and each has its own unique strengths and weaknesses.
CCD sensors translate pixel measurements by following a sequence, using circuitry that surrounds the sensor. Traditionally, these sensors were more light sensitive and produced less grainy images than CMOS sensors; however, these advantages have been slowly disappearing. The disadvantage of using a CCD is that they are analogue components that require more electronic circuitry around the sensor and, as a result, they’re more expensive to produce and consume more power.
CMOS sensors translate pixel measurements simultaneously, using circuitry from within the sensor itself. They’re more common in DSLR cameras because they’re faster and cheaper, plus they consume less power. However, CMOS sensors generally record less resolution than CCDs because they can’t physically support as many pixels on the surface of the sensor.
To keep the size of the phone to a minimum, manufactures include the smallest sensor they can without degrading image quality. The iPhone 7 Plus’s main camera includes 1/3-inch sensor, which is slightly smaller than the 1/2.5-inch sensor (7.1 x 5.7 mm) found in the Samsung Galaxy S7.
Sensors for compact cameras can start as small as 1/2.3-inch (7.6 x 6.1 mm), so it’s easy to see why smartphone cameras are making compacts less relevant. Typical compact cameras, such as the Canon PowerShot SX720 HS or Nikon Coolpix A900, have a 1/2.3-inch sensor.
The demand for higher-quality video and stills from a small camera has created the market for a more advanced compact. High–end compacts include a much larger sensor, around 1 inch, to gather as much light as possible without sacrificing size and weight. Examples include the Canon PowerShot G7 X II and Sony Cyber-shot DSC-RX100 V.
Aptly named for their large zoom range, superzooms have sensors that can range in size from 1/2.3-inch to 1 inch, and sometimes upwards to micro four thirds. Common superzoom cameras such as the Panasonic Lumix DMC-FZ2000 and Sony Cyber-shot DSC-RX10 III include a 1-inch sensor.
Also known as mirrorless cameras, CSCs use sensors that are larger than compacts, but smaller than DSLRs. CSCs cover the widest range of sensor sizes. For example, models in the Nikon 1 series use a 1-inch sensor, the PEN series from Olympus use a micro four thirds sensor, and the Canon M series contain an APS-C sensor.
DSLR cameras are the largest style of digital camera, and therefore offer the largest sensor sizes available. Most DSLRs, regardless of brand, use an APS-C sensor, but with minor variations in size. Nikon, Pentax and Sony all have the same size APS-C sensor, but all APS-C Canon models are slightly smaller. Full-frame sensors are typically reserved for high-end cameras, such as the Canon 5D Mark IV, used by professionals. However, the demand for top-quality photos and video mean some consumer-focused cameras, such as the Nikon D5600 and Canon 6D, also include full-frame sensors.