[photo-3d] Re: prescription "Holmes glasses"

["Abram Klooswyk" <abram.klooswyk@xxxxxx>]

Linda Nygren Jan 9, 2001:
>(...) On my Holmes viewer the lens centers are
> actually only about 54 mm apart; the edges are 80mm apart, but I 
> suppose the "optical center" is really at the edge rather than in 
> the middle of the lens (which is really a half lens), right?

Indeed. Often it is only a quarter of a lens, and often the optical 
axis lies in fact outside the glass.

> So you are saying that by moving two normal closeup lenses far from 
> each other so that you are using the inner half of each, that 
> achieves the same effect? 

Yes, closeup viewing lenses that is, not objectives.
 
> In Bob's case (or is it Bill?), the eye doctor apparently added a
> prismatic component to the prescription as they might for someone 
> with an eye muscle deviation problem (...)

>From Bob's quoted prescription (Jan 9, 2001, message 6833) is clear 
that cylinders (for astigmatism) are added in his normal glasses, and 
that for the stereo glasses a + 1.75 spherical power is added 
to his normal negative lenses, as well as a true prism, with 
Base Out (BO).
1.75 diopter means a focal length of 57 cm, 22.5 inch.
All in all quite complex lenses, which would cost a lot more if 
ordered separately, I suppose. But I suppose the effect is the same
as with my home made device (except for quality...).

My design is just an application of Holmes' original scheme,
which he adopted because Brewster did the same in his original
lenses stereoscope. 
 
Abram Klooswyk