Planox – The main unit

The front

The front of the unit is dominated by the two eye pieces which look a bit like a submarine periscope or a pair of old binoculars. There is one lens for each eye, separately attached to a wooden panel, and there is a number of adjustment controls. There is rack-and-pinion mechanism which moves the whole viewing box with the two lenses in and out, allowing you to focus on the slides. On the left side there is a separate double helicoidal rack-and-pinion, which symmetrically moves the two lenses apart from each other to be able to adjust the distance between the two lenses (intra-ocular). By grabbing both adjustment knobs and giving a sharp tug forward, the whole face of the unit tilts forwards, opening up to reveal the inside mechanism. It also exposes the sliding frame where the slide trays are loaded into the unit.

Right side

Obviously designed for right-handed use only, the right of the machine hosts two perpendicular sliding mechanisms. The vertical one, moves up and down to raise and lower the glass slides from the tray into the viewing position. The horizontal one has a numeric index which allows you to move the slide tray forwards and backwards, to select a specific slide.

I will describe this mechanism further in the section describing the insides of the unit – suffice it to say, that as the vertical mechanism reaches the bottom of its travel it automatically advances the slide tray to the next one. So, very much like the sliding knob of a View Master™ which uses up-and-down movement to move from slide to slide while you are viewing, when the Planox lever is at the bottom of its travel, twisting it a quarter turn to the right locks it in place, which has the effect of disengaging the lifting mechanism from the slides allowing you to slide the loading frame all the way forward and remove the slide tray.

Left side

The left side is relatively plain with one sliding small lever which is used to move an internal plate which normally covers the space between the two frames in the glass plate. This allows any notes relating to the slide to be written and viewed in that space.

On the right there is also a switch, which allows the mechanism to handle different plate sizes between 45x107, 6x13 or 7x13. Ass far as I know, it's the only scope that supports multiple formats, although I do not have a suitable tray for 45x107 to try it out.

The back

The top three quarters of the back of the unit slant upwards at an angle of about 20 degrees. On most examples of stereoscopes I’ve seen this houses a matt (opaque) glass, which is used to provide diffused light to the unit. On the Planox I have there is a light housing unit which attaches to the back.

I have seen no references to this light unit in any of the catalogues or examples of Planox I’ve found on the web, but whether it was there from the beginning or added later it’s definitely been designed specifically for the Planox. The unit easily slides on and off on two pivots, it’s metal in its construction and it just houses a light fitting and bulb.

The mechanism

(pictures to be added)

Inside the unit is a relatively simple but very clever mechanism. On the bottom, there is a metal tray which slides backwards and forwards. When at the very front position with the front lid open a bakelite tray pre-loaded with glass plate slides can be dropped into the frame, and there is a notch to ensure that it goes the right way around. Sliding the frame backwards with the horizontal lever on the right of the viewer brings the first slide in alignment with the lifting mechanism. This is unique to the Planox. In order for the system to work, all the glass slides in the tray have a metal bar attached to the top edge. The lifting mechanism consists of a set of magnets which are being raised and lowered. When at the lowest point, the magnet attaches itself to the glass slide and lifts it up to the correct position. When lowered into the tray the advancing mechanism engages and moves the tray one slot forward so that the magnet attaches to the next slide. When that is released, the mechanism pushes it up and raises the slides into view. When locked at the bottom position the tray can just slide backwards and forwards, prising the last slide gently away from the magnets, to either select a specific slide or bring it all the way to the front to load the next tray. The mechanism is not too dissimilar to the standard mechanism in slide projectors in that it moves the slide in and out of the tray slot and automatically advances the tray to the next slot. The main difference is that it works vertically instead of horizontally with magnets that are just strong enough to secure the plate without the risk of dropping it, but loosely enough to disengage easily as soon as the slide is back in the tray and the tray moved. A vertical groove on either side of the mechanism guides the glass plate from the tray from the tray slot to the right position.