I'm in the process of trying to understand lenses a bit better so I decided to take a look at the specs of an actual lens I have access to: Kowa LM25HC (datasheet).
Can someone explain the meaning of the front/rear effective diameter? At first, I thought these were the entry/exit pupil diameters, and that exit pupil was the position of the exit pupil, but this doesn't fit in with my current understanding of the concept.
Here is why.
If my understanding is correct, pupil diameter is equal to its distance from the focal point divided by the f-number. This means that, with the sizes given for the effective diameters and the smallest f-number, entry pupil would need to be $21 \cdot 1.4 = 29.4$ mm from the focal point (4.4 mm behind the object-side principal point), and the exit pupil should be $19.4 \cdot 1.4 = 27.16$ mm from the focal point (2.16 mm in front of the image-side principal point).
The drawing in the datasheet shows a point called E.P., which I assume is either the entry or the exit pupil position. It also shows points called H1 and H2, which seem to be object- and image-side principal points, respectively. Whether E.P. is entry or exit pupil, its distance from the principal points doesn't match the numbers calculated above.