Re: [Phys-l] Drugstore Reading Glasses.

[trappe@physics.utexas.edu]

Another of Ben Franklin's inventions was a pair of half glasses with  
holes drilled in the all metal bottom.  Through each pinhole a sharp  
image was formed.  This is a vsst improvement on a single pinhole  
since you get more light gathering ability.  A single pinhole  
aperture, like a camera aperature provides the greatest depth of field  
when the hole is smaller, but suffers from insufficient light.  Fading  
vision due to unresponsive rods and cones creates a losing battle.   
While you can more accurately focus with the pinhole, you still can's  
see since the light is insufficient.  I've tried the fingers/hand  
pinhole at restaurants, only to realize that the dim lit ambiance  
prevented reading the menu anyway..Karl

Quoting Bernard Cleyet <bernardcleyet@redshift.com>:

> Letter to the editor   [TPT].
>
> 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.
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l