[photo-3d] Re: Loupe question, magnifiers, confusion

[Abram Klooswyk <abram.klooswyk@xxxxxx>]

Paul Talbot 22 Aug 2000:
>What is your distinction between "lenses" and "magnifiers?"
>You seem to place loupes in the magnifier category.  Are
>camera lenses in the "lens" category?  And in what category
>are lenses used in stereo viewers?

Do I sense some irony? Of course lenses are lenses are lenses.
Only some are given special names depending on purpose.
But optical laws don't care about the names we give to lenses.

The wellknown formula for simple lenses is 1/u + 1/v = 1/f
(u - object distance, v - image distance, f - focal length).
Optical magnification then is v/u.
For complex lenses things are more complex. But still the
seize of objects on film can be calculated in this way, also
for macro.

The points is that for lenses which are hold close to the 
eyes, like glasses, loupes or magnifiers, stereoscope lenses 
and eyepieces of all kinds of instruments, a different 
magnification definition is used, depending on the arbitrary 
"normal" viewing distance of 250 mm.

George Themelis (who knows his Kingslake :-)) has explained 
everything else, I believe (also on the MF list).

Abram klooswyk