Re: [photo-3d] viewer optics

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

Brian Reynolds wrote:

> 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.

My question is, whey didn't any other design make it to a
stereo viewer?  There must be a reason for this.  What is it?

> 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

Thank you!

Here are all the designs used in 1950s viewers:

- Single element plastic (Kodaslide I, Brumberger, Life-Like, all 
   inexpensive viewers)

- Single element glass (Realist white button, some Realist handi-viewers, 
   some Brumberger)

- Double element, glass, airspaced (Some Busch and Sterling, Airequipt, 
   View-Master model D).  This is not an achromat.  It offers larger size and 
   better magnification and some eye relief but suffers from noticeable 
   aberrations, like chromatic aberration.  It also needs regular maintenance 
   because of the humidity settling between the two elements.

- Cemented doublets (achromats).  This design is found in all upper scale 
   viewers, like Realist red and green button, Kodaslide II, Revere, 
   Wollensak, TDC Deluxe.

Most modern expensive stereo viewers of European origin today 
(deWijs, Ekeren) use "double achromats", i.e. two cemented 
doublets, airspaced.  This design gives larger size/magnification 
and better eye relief than "single achromats".

So, let me repeat the question:  Why the best stereo viewers 
from the 1950s only use a simple two-element cemented achromat 
and not any fancier design?  Why only the Kodaslide II has 
coated lenses (unfortunately, inferior to other "achromats")?

> 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).  

Sounds like this is the design I call "double achromats" used 
in the contemporary European viewers. I don't think any 
manufacturer or importer/seller has called them "plossls" 
(but maybe I have missed it).

> 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.

There is an open question if this viewer uses the same lenses as the 
red button since they are both the same size and FL.  I believe
a different source was used because I have never seen a
"hazy" green button lens.  They are all clear and the quality
is consistent.

Personally, I prefer the red button viewer and optics.  I have a
basement full of green button viewers, willing to sell from
$100 to $150.  I can also enlarge the apertures for 7p viewing.  
If anyone is interested in getting one after Brian's "endorsement", 
please contact me off the list and I will get you one!

Regards,

George Themelis
drt-3d@xxxxxxx
(in heaven since he tried his new RBT 101 projector last night!)





 

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