A CMOS Sensor Size Comparison and Format Type Look-Up Table
The Image Sensor Size and Pixel Size of a Camera is Critical to Image Quality
Max Henkart
The sensor format size and pixel size of digital camera impacts nearly every performance attribute of a camera.
There are general rules of thumb for how the these will impact the image quality of a camera. Each of these will change the form and function of camera. The tradeoffs tend to be uniformly continuous over multiple degrees of freedom.
Each camera application has different 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 trends of sensor-type adoption by industry.
Digital Camera Sensor Format Types are confusing because of Cathode Ray Tubes
The format type of a digital camera sensor is one of the most confusing and ridiculous concepts in the vision industry. This is a result of approximations made in the early-to-mid 1900s when electrical-based sensors were first invented.
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, reducing 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.
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.
We surmise (perhaps incorrectly) this may have been a result of the manufacturing process for early television cathode ray tubes. Other experts in our network have noticed that the equation is approximately divided by the square root of 2, however, it is still unclear to us what the original motivation was.
What this means when someone references 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 are calculated from the formula above:
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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