BC, i dont have ADD, my deficiencies are in other areas. i have also been reading up on binoculars on this and other forums (cant afford the unmentionable Bill book yet).
often when writing people inadvertently expect a basic understanding of terms and the physics so one can go in circles.
my understanding is that the field stop is the black edge of the circle we see. different designs place the field stop producing mechanism at the eyepiece or sometimes elsewhere internally . a baffle designed to cut back on the edge effects of cheaper glass may also be used as, or act as a field stop. i really think it doesnt matter at my stage, and possibly yours, what produces an effect, although one wants to resolve it and understand it ultimately.
if others knowledgeable of the particular device rather than generally offer solutions such as pulling back the eye, i try it and see if it affects other parameters. in my case it does, the 8 effect grows, movement in and out of the hinge does not fix this in fact black areas appear in the fov and eye angle is more critical. so in my case the shiny ring of rainbow is something i have to accept. you dont, sell the things, you have plenty more, and to use an analogy, if your Ford is good and you also have a Toyota, when you try the Suzuki and find the view invthe screen is wonky, well get rid of it! you can always try a Hondanext week ....
dont take that as condescending, i know you like to talk and learn, but why waste your time on the Suzuki? i used that analogy because you once owned a spanner. you can go back to optical physics anytime you wish and ignore me. i would rather leave it to Bill and the others. and i cant find your comparison review, did you write it?
and a final btw i need a millionaire gf, i need an intro please ....