In photography, it's the accepted norm to say that if you know the sensor size of your camera and the focal length of your lens, then you know the field of view of your system.
However, in optics, it's well known that for a fixed sensor size, the distance from the lens to the image plane (which we can equate with the flange distance) also affects your field of view. Everyone who mounted his\her lens on a macro adapter had seen that increasing the flange distance will narrow down your field of view, and they will end up with a macro lens.
So my question is why do we characterize lenses with the focal length and not the effective field of view?
I realize that it could be the case that it was just an arbitrary historical decision, but I'm curious whether there's justification for that which I'm missing.
I want to make a few things clear in light of some of the comments I got.
From the physics POV of it all, what determines the effective FOV for a given sensor is the effective focal length of the lens and the distance between the back principal plane of the lens to the sensor, which is determined unambiguously by the distance between the principal plane and the flange of the lens plus the distance between the flange of the camera and the sensor.
These two properties are completely independent of each other, but changing either of them will change the effective FOV - this is a fact of geometrical optics.
My question was: given that both parameters affect the FOV, why is it then that we attribute only the focal length to the FOV of the lens?
To further clarify by an example: you can have a 50mm and a 40mm lenses both with the same distance between the principal plane and the flange of the lens. In this case, if you place the 40mm lens sufficiently further from the sensor (compared to the 50mm lens) you will have the same effective FOV.
Please try to answer my original question instead of trying to educate me about optics - that part of the conversation I got down pretty good :)