Objective lens diameter vs effective lens diameter

[Kendall Sorensen]

I was looking at specs on the new Maven RS1 1.2 2.5-15 the other day and I saw something I don’t recall ever seeing in the long years I’ve been looking at riflescopes.
The scope specs list “effective objective lens diameter” as 28.5 mm @ 2.5x power, and 44mm @ 15x power. I’ve been a sorta serious photographer for 50 years, bought my First Nikon FTn in 1968, regularly visit sites like CloudyNights, have owned multiple dozens of riflescopes in my lifetime and I have a pretty good understanding of the physics of lenses and yet this particular spec is something new to me.
Is there something in the function of a FFP riflescope that changes the effective diameter of an objective lens at different power settings?
At 74 years I admit there are still things to learn and am hoping for some enlightenment here. Grazi

 

[4th_point]

The Dark Lord could answer properly, but I think it has to do with the fact that only a portion of the objective is actually being used on low magnification because the quality of the FOV would be compromised otherwise. That's why many LPVO have small objectives.

In order to use more of the primary image, and maintain good image quality across the field, it would require a bigger and more complicated design.

The DLOO, ILya Koshkin, has written about it and I think he has a video about it.