Field of view is not printed on the lens. It is born when a focal length meets a sensor size. Change either one and the number moves. A 4 mm lens on 1/4" is not the same view as 4 mm on 1/2.5".
In one sentence. EFL sets how strongly the lens magnifies. The sensor rectangle crops that drawing. FOV is the crop.
Why catalogue FOV lies
Lens makers often quote FOV on one favourite format. Sometimes they quote a diagonal. Sometimes they quote a fisheye number next to a rectilinear number as if they were cousins. They are not. Projection changes the meaning of the degree.
If you need a number, compute it from EFL, the active width (or height, or diagonal), and the projection. Or use the Camemaker configurator, which already does the marriage.
The corridor test
Stand in a hotel corridor. A short EFL shows two walls, the carpet, and the door. A long EFL shows the room number. You did not change the corridor. You changed how much of it was allowed onto the chip.
Now swap to a smaller sensor and keep the same lens. The picture jumps toward the room number. People say the lens "became tele." The glass did not change. The crop did.
HFOV, VFOV, DFOV
Horizontal is what a robot usually cares about (the aisle). Vertical is what a doorbell cares about (the visitor and a bit of sky). Diagonal is the largest number, so it wins arguments and loses designs. Say which one you mean.
How to use Camemaker
Pick the sensor format first. Then in the lens library filter EFL, and treat any FOV printed on a random datasheet as a hint until you know which sensor it was measured on. Keep projection in the same thought: a 180° fisheye is not a 180° rectilinear lens that someone forgot to correct.