Quote Originally Posted by Mark Sawyer View Post
I've never heard of a photographer who knew exactly where his nodal points were for a particular lens, much less use them.
Absolutely correct*.

That's why lens data sheets show the Flange Focal Distance, which is from the lensboard to the film regardless of node location.

With some telephoto designs, the second (rear) node is in front of the front element by many centimeters.

Quote Originally Posted by Mark Sawyer View Post
The aperture would be the diameter of the opening of the lens measured through the entrance pupil (front element). Which designs does this not hold true for?
Correct again, for all lens designs.

I was clarifying that the dimension used was not the physical diameter of the diaphragm blades at an f-stop setting.

You can measure the aperture physical diameter with a pair of calipers, but that's not the value needed for the calculation.

- Leigh

*NB: One exception is panoramic photography using multiple images.
For this technique the vertical axis of rotation of the camera must pass through the front (first) node.