The Black Box
A Medium Format 3D Viewer for Transparencies

The project uses a pair of loupes permanently attached to a 7 inch by 5 inch by 3 inch plastic project box. The box itself contains a holder for the slides, the 5500° K fluorescent lamp from a 4x5 light box, and a battery pack.

The loupes are KMZ/Horizon 4x designed to cover a 2 inch by 2 inch area; eyepieces are 29 mm. diameter. While not adequate for general medium format use, they do (barely) cover the 50 cm. by 50 cm. area of the typical mount. I could have used Horizon's larger medium format loupes, which are only marginally more expensive (and marginally superior optically), but I knew from the experience of others that it would be necessary to rework the mounts in order to mount two of them closely enough together to obtain the desired 62 mm. interocular distance, which centers each lens directly above the chips of the typical mount.

Slide mounts fit into a channel which includes two springs (fabricated from piano wire) which press against the edges of the slide mounts to keep them at a uniform distance from the lenses and prevent focus changes as the viewer's orientation changes. As constructed, the viewer will accommodate mounts up to 3.5 mm. thick.

The illumination mechanism was taken from a 4x5 light box originally powered by four AA cells. The reflector was both cut down and bent at a sharper angle to fit into the box, and the diffuser was also cut down to fit; it is now positioned about 1 cm. (3/8 inch) behind the focus point. Positioning it farther away was desirable for keeping any dust which lands on it out of focus, but my desire to keep the spacing between the diffuser and the lamp at a maximum (for more even illumination), combined with the size of the box, prohibited this.

An on-off-on switch with dual LED pilot lights lets the user choose between momentary and always-on modes for the lamp; the pilot lamp for always-on mode flashes to remind you it is on (which is not obvious, as the box is well-sealed against light leaks).

The four D cells, in a removable battery holder, provide exceptional life. I am still using the original set.