I don't get it. Why would you need this? Even if one eye is slightly higher or closer to your nose than the other, your total IPD is still a linear distance.
--AP
AP,
If you have an SE and had eyes that were not equidistant from the center of your nose, you'd get it all right. Right between the eyes.
While my total ID is a linear distance, it's not the same linear distance as the total IPD distance from the center of the SE's exit pupils. With the SE's EPs having spherical aberration of the exit pupil, eye placement is critical. BOTH eyes need to be centered on the exit pupils, but if one eye were farther from the center post than the other, you wouldn't be able to align them BOTH at the center of the exit pupils. You can do only align your eyes with one side or the other.
There is a bit of latitude, though. If I move my left eye off center toward the left edge of the eyecup and keep it perfectly positioned, I can avoid image blackouts.
In addition to my right eye being a few mm farther from the center post (and the bridge of my nose), it's also a few mm deeper set. It's not so freakishly asymmetrical that one would notice the difference like I do on
Shannon Doherty, but just enough to cause image blackouts with the SE if my eyes are pressed against the eyecups (I just bought a new pair of SE eyecups, and I"m noticing this more).
Similarly, the Vixen 7x50 Foresta is prone to image blackouts (just ask mooreorless!) with the original eyecups on. The image in my left eye kept blacking out because that eye is a few mm closer to the EP. After I took the original rubber eyecups off their metal frames, which made the diameter of the eyecups uncomfortably large, and dropped old, fold down rubber Swaro eyecups inside the metal housing, I could see the entire FOV w/out image blackouts since it placed my left eye beyond that critical point.
BP