"Right" iris position?

[Andrey Vorobyov]

Are there any rules that govern the iris placement along the lens axis?

If the iris is placed too far, it acts rather as a vignetter rather than as an aperture. On the other side, telephoto lenses have rear node outside the lens but the iris is inside of course.

Is there a "correct" position for the iris and what are the reasons?

Thanks
Andrey

[Mark Sawyer]

Yes, it influences field curvature, coma, and pincushion and barrel distortion. While it "theoretically" goes at the rear nodal point in a normal compound lens, it is often moved slightly, especially in older lenses, according to the designer's priorities.

[Andrey Vorobyov]

While it "theoretically" goes at the rear nodal point in a normal compound lens..

Mark, but this is obviously not true for telephoto lenses..
Can you give any references to that theory that states the the rear nodal point is the preferred position?