How do the optical format and sensor format and affect the Field of View?
The optical format decides the size of the image circle where the whole field will be squeezed into, and the sensor format decides the rectangular area to catch the image circle. In most camera setups, the sensor rectangular area crops a section inside the image circle.
In an ideal case, the optical format would equal the sensor format, where the sensor’s diagonal equals the image circle’s diameter, so the diagonal field of view of the sensor (DFoV) equals the native FoV of the lens.
It’s also common to have a lens with a larger optical format than the image sensor format. However, the field outside the sensor rectangle will be missed, resulting in a smaller field of view. With lenses of the same optical format, the smaller the sensor is, the smaller the field of view we will get. If the optical format is smaller than the sensor format, dark unexposed surroundings will occur, but it’s helpful to capture the whole field of the fisheye lenses.