The sensor format size and pixel size of digital camera impacts nearly every performance attribute of a camera.
The format size is a key element that contributes to system constraints across the low-light performance, dynamic range, size, cost, power consumption, lens requirement, number of pixels resolution, etc. Each of these will change the form and function of camera.
There are general rules of thumb for how the these will impact the image quality of a camera. The tradeoffs tend to be continuous and very inter-related across many degrees of freedom.
Every camera use-case has application-specific requirements, so the selection of a CMOS image sensor needs to be made on a case-by-case basis. We've done our best to categorize the usage of sensor-type by industry.
Digital Camera Sensor Format Types are confusing because of Cathode Ray based Vidicon Tubes
The format type of a digital camera sensor is one of the most confusing in the vision industry. The format type is a remanent from how video camera tubes were constructed prior to the advent of CCDs or CMOS sensors.
These 'video tubes' had opaque regions outside the active area of the cathode tube, which reduced the light sensitive region. These resulted from the mechanics holding either the larger tube or cathodes.
For example:
- A 1″ image sensor with 4:3 aspect ratio is 12.8mm Horizonal * 9.6mm Vertical * 16mm Diagonal
- A 1/3″ image sensor with 4:3 aspect ratio is 4.8mm Horizontal * 3.6mm Vertical * 6mm Diagonal
Well that doesn’t seem to make any sense, does it? 1" is 25.4mm and 1/3 of 1" is 8.5mm! Even 1/3 of the 1" Format Diagonal should be 5mm!
Let's take the 1" format type as an example. Part of the cathode ray tube's diameter was the tube wall and was not used for imaging purposes.
So, the area was reduced from 25.4mm to 16mm.
So, a lens suitable for a 1" type cathode ray tube did not need an image circle that extended to the entire 25.4mm tube diameter.
Some historical references state that the sensor size is 3/2 * Format Type then rounded, however, there are still exist many discontinuities.
With modern day imaging, there exist a nearly infinite number of image sensor diagonal dimensions for which there was no corresponding original video tube size.
So, we've done our best to derive a "modern-day" equation that defines image sensor format type more precisely. We used commonly agreed upon datapoints of 1" = 16.0mm, 1/2" = 8.0mm, 1/3" = 6.0mm, 1/4" = 4.5mm and backed out a fitting equation, then cross-referenced as many other articles as possible.
Unfortunately, the formula for the digital image sensor type has a discontinuity occurring between the 1/2" image sensor and 1/2.3" image sensor format size.
What this means when someone provides a CMOS Image Sensor Format Type
This subjective classification means that manufacturers can apply 'best judgement' when publishing a Format Type for their sensor.
The means that engineers should use the exact output pixel count and pixel pitch (size) when considering a lens, such as a CS Mount Lens or M12 Lens.
The majority of sensors on the market approximately adhere to the Format Type dimensions below, which can calculated from the formula above:
Download The Format Type Look Up TableCalculate the "35mm Equivalent" EFL of any lens on any sensor
We've created a simple calculator to help translate between engineers and hobbyists who use the "35mm Equivalent EFL" when discussing Field of View.
If you are looking for more advanced functionality and calculations, please see our more advanced Field of View calculator which includes distortion.
The Take-Away: There is no substitute for exact values when selecting a lens
Most manufacturers are consistent and accurate with their Format Type classifications. However, we've run across numerous specification sheets which are mis-classified.
To repeat, always use the exact output pixel count and pixel pitch (size) when finding a lens!
If you've figured out which sensor you're using and want to calculate the 35mm Format Type Equivalent EFL, check out our Camera Field of View Calculator.
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