I read with interest Dr. Erlich's description of restaurant use of a
stenopaic finger. This is the first time I have read a description of
what I did for about a decade. I can no longer do this, unless I'm
wearing my hyperopic glasses, as I've become two diopter hyperopic plus
about four presbyopic. Earlier I found one need not necessarily use an
aid. Simply look down one's nose and tip one's head back until the
desired degree of stenopaia is achieved. One may reduce restaurant
embarrassment by punching the appropriately sized hole in a business
card. A wood pencil is ideal. A European immigrant showed me his
stenopaic lorgnette just at the time I noticed my presbyopia, this
prompted my finger discovery.
I'm not familiar with a pinhole as being a magnifier except in the sense
as geometric magnification. An interesting exercise is to calculate the
optimum f stop, because, as the depth of field (focus) increases, so
does the diffraction. Such diffraction is quite evident when looking at
mercury or sodium street lamps with a stenopaic finger.
bc
p.s. I think the etymology of stenopaic and presbyopia quite interesting.