Don Lopp wrote:

> Hi Chuck:
>
> Thanks for straightening me out. I do agree with your explanation, but
> I do not see a significant advantage in gaining only one mm of screen
> width, when the basic width is already 58mm, which I did not realize was
> the case until I just looked it up on the Dr T web-site. My camera
> has a 3/4th inch wide RED window, such that my stereo pairs can have a
> total width of up to 5 1/4 inches, whereas a standard RED window
> restricts one to having a max width of 5 inches, or less.
>
> As far as viewing problems I fail to see why the resistance to viewers
> having an adjustable interocular. Having an adjustable interocular
> permits one to use smaller diameter viewing lenses which are cheaper,
> and they usually produce much less distortion, as is the case with the
> excellent, Chinese viewer lenses.
>
>
> Best regards,
>
> DON
>

--- In MF3D-group@yahoogroups.com, Don Lopp wrote:

> > As far as viewing problems I fail to see why the resistance to viewers
> > having an adjustable interocular. Having an adjustable interocular
> > permits one to use smaller diameter viewing lenses which are cheaper,
> > and they usually produce much less distortion, as is the case with the
> > excellent, Chinese viewer lenses.

No doubt an adjustable interocular is useful for slides mounted "to the window" where the
infinity spacing is left to "fall where it may". To get such slides to view with a parallel view
to infinity, the interouclar must be adjusted to whatever the infinity spacing is in that slide.

As for me, I would prefer slides mounted with a 65mm infinity spacing used in a viewer
with 65mm interocular spacing. They go well with my 65mm (average for the population)
eye spacing. As long as I have 65mm infinity spacing on the slides and the viewer is at
65mm spacing, I do not need the adjustment.

It would no doubt cost more to make viewers with adjustable interocular and so a standard
infinity spacing could save us a lot of money as well as the aggravation of adjusting the
interocular for each slide.


Chuck Holzner

Charles F. Holzner wrote:

> As for me, I would prefer slides mounted with a 65mm infinity spacing used in a viewer
> with 65mm interocular spacing. They go well with my 65mm (average for the population)
> eye spacing. As long as I have 65mm infinity spacing on the slides and the viewer is at
> 65mm spacing, I do not need the adjustment.

I believe that you are missing an important point. When using a
stereo viewer which has an adjustable interocular, one can view all 3D
slides which have been mounted with a 65mm infinity spacing as easily as
can one who is using a viewer that has a 65mm infinity spaced viewing
lenses. !

Viewers with an adjustable interocular allow one to mount and to view 3D
slides which are not mounted to having a 65mm infinity basing.

By mounting to infinity, one can avoid producing 3D slides which may,
and often do, contain window violations.

As I mentioned before, having an adjustable interocular permits one to
use smaller diameter viewing lenses that are likely to produce less
distortion than do the wider diameter viewing lenses.

An example is a 78mm lens which has a 46mm diameter viewing lens, an
f/1.7 lens. Based on the many samples that I have seen in many MF
viewers, these lenses are not free of easily visible optical
distortions. It is difficult to design a distortion free, 2 element,
f/1.7 lens

A 75mm fl. lens with a diameter of 31mm, is a slower, f/2.4 lens, which,
in the case of the ones I have seen in the Chinese viewers, show much
less distortion than do the, faster, 78mm viewer lenses that I have
seen, to date. Plus they are much less expensive, ( by about 1/2),
and much lighter. It is easier to correct a, slower, f/2.4, 2
element lens.

> It would no doubt cost more to make viewers with adjustable interocular and so a standard
> infinity spacing could save us a lot of money as well as the aggravation of adjusting the
> interocular for each slide.

I believe the first priority in designing a MF stereo viewer should be
an easy, to operate, focus capability, an example being the MF viewer
designed and built by Sam Smith. My experience indicates that an
adjustable interocular is, also a valuable asset in a stereo viewer.
I cannot imagine using a 35mm 3D viewer that did not have one,
(Brumberger), and I would not build any 3D viewers that did not offer
both a controllable interocular, plus an easy to operate focus mechanism.

The cost to have a controllable interocular could have been close to
zero, if it had been designed into most of the MF 3D viewers that I
have seen, in the last 8 years. IMO, the cost savings made by using
smaller diameter viewer lenses would have been more than enough to
compensate for the cost of an easy to operate focus mechanism and a
controllable interocular.

Apparently, I was fortunate that I designed, and built, my first MF
camera and my first MF viewer in 1995, 5 years before I found the
internet, and was therefore, able to plan independently.



Best regards,

DON