hi gijs --
for me, focus past infinity i can check approximately with my eyes and eyeglasses. with glasses, there should be substantial focus travel left in the focuser if I am looking at, say, the Orion nebula. if the focuser stops just where my corrected vision can bring it to focus, I know there is very little focus past infinity and I cannot use the binoculars.
if there is some travel, then I take off my glasses and try again. if the focuser stops before both eyes are able to get to focus, it usually means there is about 3-4 diopter of overfocus, which for me is not sufficient.
I picked up a pair of +5 reading glasses recently, thinking that by putting them between my eyeglasses and oculars, I should be able to reduce overtricks by 5 diopters. it sort of works as a crude test, but the eye relief required for it is very high.
I was hoping there was a way to quantitatively measure it, and perhaps see if a binocular that could focus closer than spec was compensating for that by losing some of the overfocus in its spec.
kimmo in another thread made an excellent point about focusing past a relatively nearby pinpoint light source and setting how many diffraction rings are formed as a way to compare available overfocus between binoculars. I don't know if there is a way to make that a quantitative measure as one can with near focus, though.
so for now I'm working with maven. they are willing, for an additional fee, to assemble binoculars that have overfocus beyond their normal range.