[photo-3d] Realist green-button viewer - part 2

["John Goodman" <jgood@xxxxxxxx>]

Preaching to the choir again.... But if there are any budding 
viewer aficionados lurking, who have not had the chance to use 
a Realist green-button viewer in fine fettle, with 5p slides, you 
have a treat in store.

When overhauling a green-button, the interocular and focus 
adjustment mechanisms may require attention. Both are quite 
special, and can perform superbly if they work properly.

If the interocular adjustment mechanism does not work 
properly, the desired adjustment will not hold, because the left 
and right lenses are drawn toward each other by strong 
springs. A hollow rivet acts as the axle for the green plastic cam 
wheel that adjusts the interocular spacing. It's staked to the 
metal piece that guides the horizontal movement of the two 
lenses, and a spring washer under the rivet head is supposed to 
apply the correct amount of friction to the rotation of the knob.

The interocular adjustment of my viewer would not stay put, 
and it seemed a losing battle to fix the mechanism, which has 
no adjustments. (It would be a mistake to try and stretch the 
springs to weaken them, because then the lenses wouldn't 
return to their closest together position.)

I noticed that the rivet itself was rotating when the knob was 
turned. Strongly pressing the corner of a flat bladed screwdriver 
tip against the  mushroomed flange of the rivet deformed the 
metal and stopped this rotation, restoring the required degree 
of friction so adjustments now hold.  Hooray.

Imho, both the interocular and focus adjustment mechanisms 
of the Realist green-button viewer are very clever designs, 
especially the focus. The reason? Zero backlash! The springs 
ensure that any play in the moving parts is removed. The 
focusing wheel's spiral track and first-class lever follower that 
moves the slide holder is brilliant, as the adjustment motion is 
both fine and precise, with no play in either direction.

I was initially bothered by stiffness in the focusing adjustment 
wheel action, and by the slide carrier's not moving smoothly 
enough when close to the lenses. I had re-shaped the arched 
spring that keeps the bulb side of the slide carrier pressed 
against the plastic body, to apply a more force (since the carrier 
was wobbly before). All of these details are nicely illustrated in 
DrT's manual (pages 12~14).

To cut to the chase, I couldn't get a nice smooth action with 
just petroleum based lubrication, but a tiny bit of powdered 
graphite in the right places worked wonders. Friction behavior 
can be mysterious, but "stiction" spoils the feel of a focusing 
mechanism. (Stiction meaning that the static friction of the 
sliding surfaces is noticeably greater than the dynamic friction. 
Things stick until a certain amount of force is applied, then 
suddenly slide, making short range movement difficult.)

(to be continued)

John Goodman

 

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