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

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

>In several years of reading a few
>different 3D lists, the only magnification formulae I've seen
>are the 250/fl you mention, and 250/fl + 1.  What is the
>reasoning for the +1?

When you focus the viewer you can focus it for your
eyes in the relaxed stage (looking at infinity) or
you can focus it for your eyes accommodating (i.e.
focusing close, strained).  In this second case
you see a larger image because you have reduced
the distance between the slide and the eyes.  Then
you should use the +1 factor (which gives a higher
magnification).

Personally, I always focus the viewer at infinity
(relaxed viewing) EVEN IF I am looking at a close
up of an object!  Therefore I prefer the formula
without the +1.

It takes a little bit of training to learn how to
focus viewers, microscopes, telescopes, etc.  Many
inexperienced users just mess up the focus and
interocular adjustment, that's why I don't encourage
them to change anything when I pass the viewer around
(another reason I am known as DrT, Dictator of 3d! :))

George