I have tried to make sense of sensors, and address the question, Is a bigger camera sensor better?
What is a Camera Sensor?
It is the digital equivalent of film. It captures light and converts what you see through a viewfinder, EVF, or LCD screen into an image.
How does a Camera Sensor Work?
A camera sensor uses millions of tiny light cavities or “photosites” to record an image. When the shutter is pressed photosites collect photons and store these as an electrical signal. (Photons are particles which transmit light i.e. light is carried through space by photons. That is all we need to know!) The more photons that are collected by the photosites the stronger the electrical signal. The different signal strengths across the millions of photosites are then converted into digital values. This is capable of being converted into a greyscale image, however not a colour image because photosites are unable to distinguish how much of each primary colour they have recorded.
What is the Difference between a Photosite and a Pixel?
Pixels and photosites describe the same light cavity on a camera sensor. However, pixels have also come to describe the smallest element of an LED screen. Which is the display side of the sensor rather than the light capture element. So pixels describe both and this can cause confusion. Camera manufacturers refer to sensor size in terms of megapixels (i.e. one million pixels). For example, a 21.1 megapixel sensor is 5616 photosites wide by 3744 photosites high.
How does a Camera Sensor Capture Colour?
Each photosite is in effect colour blind, only recording the total intensity of the light that strikes its surface. To capture colour images, a beam splitter is placed over each photosite. to filter the light so that only one primary colour is allowed through. The other colours are discarded. This colour filter array was invented by Dr Bryce E. Bayer, a scientist working for Kodak. He invented the particular red, green and blue arrangement of colour filters to capture colour information.
The red filters, for example, will only allow red light photons to pass into the pixel below it. Each line on the array has only two of the primary colours either red/green or blue/green. The camera then uses an algorithm to work out the colour of each pixel. In fact, it combines a 2×2 square of four photosites together to predict the colour and its intensity.
How Big is the Camera Sensor in Your Smartphone or Camera?
The graphic above is from PhotoSeek.com and compares different sensor sizes.
Smart Phones Sensor Size
Smartphones utilise very small sensors. As an example, the sensor size on an Apple iPhone 7 is 1/3inch, 12megapixels, pixel size 1.22 microns. Diagonal measurement 6.0mm, area 17.3 square mm. A full frame sensor is 55 times bigger.
Compact Cameras Sensor Size
A Canon Powershot has a sensor size 1/1.7inch, 12megapixels, pixel size 1.9 microns. Diagonal measurement 9.3mm, area 41.51 square mm. A full frame sensor is 21 times bigger.
Micro Four Thirds
This is a sensor size widely used on Olympus and Panasonic cameras that was introduced in 2008 to create smaller camera bodies and lenses. For example, the Olympus PEN F has a micro four thirds sensor, 20 megapixels, pixel size 3.3 microns. Diagonal measurement 21.6mm, area 225 square mm. A full frame sensor is 3.8 times bigger.
Widely used in SLR cameras. For example, the Fujifilm X-Pro 2 has an APS-C sensor, 24 megapixels, pixel size 3.9 microns. Diagonal measurement 28.2mm, area 370 square mm. A full frame sensor is 1.54 times bigger.
Used on digital SLRs and mirrorless camera. For example, the Nikon D600 has a full frame sensor, 24 megapixels, pixel size 6.0 microns. Diagonal measurement 43.2mm, area 860 square mm.
So Does the Camera Sensor Size Matter?
A bigger sensor is better for two reasons. Firstly the bigger sensor can capture more light, which means more detail, better colour rendition a sharper image and more depth of field. Smartphones can take great images, but the sensor on a full frame camera is 55 times bigger, and that is a lot more light. Secondly, the size of the photosites/pixels does matter. On full frame cameras, the increase in pixel size means that manufacturers can offer amazing ISO performance, which means better low light performance and more dynamic range.
It is therefore important to make a decision on which camera to buy, not based just on the sensor size measured by the number of megapixels. It is also the size of those pixels that count. A smartphone may be 12 megapixels, but the pixels are small about 1.55 microns compared with 5.2 microns on a similar size APS-C sensor.
Camera manufacturers are a bit vague on pixel size. This may be because there is a trade off, between the area of the sensor and the size and number of pixels that it can contain. As full frame sensors gradually creep towards 30 megapixels and beyond, this may be close to the maximum based on current technology. For photographers and camera manufacturers, yes, it is all about size!