Re: [photo-3d] viewer optics

[Brian Reynolds <reynolds@xxxxxxxxx>]

George, I really wish you would include the attributions (i.e., lines
like "XXX wrote:") when you reply to someone so that we can tell who
you are replying to.

I've inserted the attribution to Peter Abrahams below.

George Themelis wrote:
>
> I am sorry, I am not an expert in optics but I do have
> a few questions....
> 

A good introductory discussion about eyepiece optics can be found in
Sam Browm's "All About Telescopes" from Edmund Scientifics
<URL:http://www.scientificsonline.com/>.  They also have Sam Brown's
"Popular Optics".

> >Peter Abrahams wrote:
>
> >Instead, we should compare them with other types of eyepieces that
> >were standard by the 1950s, in binoculars, telescopes, and
> >microscopes -- even inexpensive models.  These were vastly better &
> >show that the technology was available to produce a much better
> >product.
> 
> How about if we compare them with other stereo viewers
> (with achromatic lenses)?
> 

I believe that Peter's point is that there were other, better optical
designs available at the time.  Comparing several viewers of the same
design will not show you how a better design could improve the viewer.

"All About Telescopes" has diagrams of several eyepiece designs.  I'm
not sure how much more expensive these designs might have been.  Does
anyone have an Edmund catalog from the 1950's?

> >astigmatism (fuzzy edges), and curvature of the field (focus mid
> >field, then to focus at edge of field you have to turn knob) to a
> >degree that could have been inexpensively corrected in the
> >1950s.   
> 
> Are there any other stereo viewer lenses from the 
> 1950s without these "features"?  If I buy a pair
> of "modern" achromats from Edmund Scientific (and
> pay about as much as the entire red button viewer,
> just for the pair of lenses) would these problems
> be absent?
> 

You need to distinguish between the optical design and the design
goals.  "Achromat" is not a design.

The design that I think you are referring to is a cemented doublet
(i.e., two optical elements (a double convex and a concave/convex)
made of different optical materials cemented to each other at one
surface).

An optical design is achromatic if it can focus two different
wavelengths of light (usually red and green I think) at a single spot.
Not all achromats are cemented doublets.  Hopefully all doublets are
achromats (otherwise why bother).

By the way, Edmunds is not a place to shop for bargains.

> >They could also have been made with enough eye relief to allow for
> >use with spectacles,
> 
> I was under the impression that achromatic lenses
> have zero eye relief, meaning that the minute you
> start moving the eye away from the lens, you see
> less and less.  
> 

Again that's a distinction between the design and the desing goal.
Doublets may have zero eye relief (I don't know for certain), but not
all achromats have the same eye relief.  For example, plossls (a
design using a pair of cemented doublets with the double convex
elements facing each other) are known for having good eye relief and a
good field of view (50 degrees).  Naglers have a huge field of view
(80 degrees), but shorter eye relief.

By the way, in the time that I've been involved in stereo photography
last month's Third Friday Dinner was the first time I saw a Realist
viewer that had really good optics.  It was a green button viewer.

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
reynolds@xxxxxxxxx              | "Oooh!"
http://www.panix.com/~reynolds  |    -- Dexter and Dee Dee
NAR# 54438                      |       "Dexter's Laboratory"

 

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