Neima, Matt wrote:

> What are the best choices for illuminating
> the slide (fluorescent from a light panel?).

This kind of depends on how it will be powered.

I kind of like the look of a fluorescent light
but they have some draw backs. They require a
high-voltage power supply which creates complexity
and reduces efficiency. They also require some
time to get up to full-brightness. This later
fact means the light really needs to be on for
the whole viewing session which further reduces
its efficiency. If you have lots of power
available, these factors are probably moot.

I kind of like the low power requirements and
instant-on behavior of LEDs but color temperature
can be problematic. If you have a little bit of
power available, I'd probably use these.

I really like the color temperature of halogen
bulbs. They come up to full-bright fairly well
and are easy to wire. But, going this way
requires a more complicated (IMO) reflector and
diffuser arrangement than LEDs or edge-lit
fluorescent panel. This solution is less efficient
than LEDs but is well understood.

If I were designing, I'd try to design in LED
illumination which was powered by a charge-in-place
cell-phone battery. I would incorporate a large,
easy to see and use momentary power button (like
the Red Button) and I put a battery-check led or
meter of some kind on it.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Neima, Matt wrote:

> I have not been able to find decent
> quality rack and pinion gears suitable for this.

What about using a threaded shaft rather than a
rack and pinion?

> Do the measurements (for focusing and slide to
> diffuser distance) sound right?

Placing the diffuser close to the slide means
that dirt on the diffuser will be more likely to
be in focus (and therefore distracting). But,
it also means your viewer will be shorter, lighter
and easier to handle.

Placing the diffuser farther away from the slide
means that dirt on the panel will be out of focus
and less distracting. But, this means your diffuser
needs to be larger and your light source needs to be
brighter.
--
John Thurston
Juneau Alaska
http://stereo.thurstons.us

Message> I currently use the 3D World plastic viewer for myself and an
antique focusing viewer (very similar to the Heidoscop viewer, I think it's
a Zeiss Ikon of some type).

> Comparing a slide viewed in the two viewers presents a dilemma - I like
> the extra magnification of the plastic viewer, but the view in the antique
> viewer seems much better. And I don't know why, any ideas? I'd like to
> figure out if this is a focal length issue, or a lense quality issue, or
> something else. I think the answer to this question will impact the viewer
> design.

You should make an effort to answer this question for yourself.

First of all, it is difficult to compare viewers with different focal
lengths because the different stereo impressions created from the different
focal lengths can impact your judgment.

The quality issues associated with each lens relate to issues like 1)
aberrations, 2) distortion.

I think the 3D World lenses are as good as achromatic lenses get. I doubt
that the Zeiss Ikon viewer has better lenses.

The other issues involved are 1) lens spacing (interocular), and 2) focal
length (magnification).

Why do you think the Zeiss lenses are better? Do you see less distortion?
Do you see false colors in the 3D World viewer? Do you see more sharpness
in the edges in the Zeiss lenses. Is the image more stable as you shift
your eyes around? If you cannot tell for sure, then I think it is the focal
length and spacing of the lenses that affects your judgment.

George Themelis