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Camera Sensors – Why Size Matters

Are you in the market for a new camera and totally confused by the industry lingo regarding sensor size? You may hear things like full frame, aps-c, crop sensor, 4/3, micro 4/3, nikon 1, 1/1.7, 1/2.5, 1″ and many more!

So what’s this all about?

Let’s start by going over what these measurements and phrases are about: the size of your camera’s sensor. Size (in digital imaging) matters because the larger the size the more light can be collected by each pixel (if each sensor has the same number of pixels). Back in the days of film the size was a 35mm negative, which measured 36mm wide by 24mm tall. This sensor size is refereed to as full frame as it covers the same physical size as an old 35mm film negative.

The list below goes over each sensor size (in millimeters), the crop factor (what your multiply the lens focal length by to get the measurement in traditional 35mm cameras lens) and the popular cameras using that sensor size.

So why does this matter?

Two reasons: Light collection ability and crop factor.

Light collection ability increases as sensor size increases. The bigger the sensor the more area it has for collecting photons of light. If each sensor has the same number of pixels then the larger sensor has more photons collected per pixel to measure then the smaller sensor. The more photons the greater the accuracy in the measurement and lower the noise you will see especially in low light. Sensor design and lens design have a large effect, but this larger being better is true for two sensors of the same generation in terms of noise and signal quality.

Crop factor is the part of the image the sensor sees or “crops” out of the image the lens produces. Some lenses produce an image the full size of a traditional 35mm piece of film, while others are custom made to fit the size of the sensor. This is why a lens may say 4.3mm to 32.5mm in a point and shoot, but the image you see looks like a 24 wide angle to 180 telephoto lens from a 35mm camera. In the image above the various sensor sizes are superimposed over a picture of the American flag at the Wall Street Stock Exchange in New York City. The green is the “full image” the lens produces as seen by a 36x24mm sensors, and each one of the smaller sensors “crops” a portion of what the lens would see. This is why camera phone lenses can be so small – because they only need to produce an image big enough to cover the smallest inside box where as a 35mm SLR camera needs to produce an image to cover the largest sized box. This is also why buying a 35mm lens to use on a Canon T4I produces an image that has same field of view of a 56mm standard lens instead of a 35mm wide angle lens.