I made this replica of Holmes stereoscope for a friend doing vintage photography. For stereographic photos, he uses a stereo camera from 1950s. The stereoscope is designed for 180 mm wide photos.

I made also a case for the stereoscope: https://www.thingiverse.com/thing:4686740

The body is made of two pieces pieces to fit my printer bed. The handle is printed in two halves for added strength. The swivel is positioned for printing to align the layers for added strength. Printing the swivel may require supports. Otherwise this should be an easy print.

Additional material needed:
A pair of 1.5" square stereoscope lenses
Thin metal sheet for the spring of photo holder (see image, I used a piece of tin can)
Two bolts 2 mm dia, 4mm long to attach the spring
One 3 mm bolt and nut for the swivel
Metal wire for photo holder (see images)

After printing, glue body parts together and handle halves together. Treat the individual parts according to taste. I tried to replicate a slightly weathered version of a stereoscope.
Prepare a plate spring for the photo holder and screw it in place. Bend the metal wires and glue them in the holes of the photo holder.
Glue the lenses on the frame. Glue the swivel and the lens frame on the body. Attach the
handle with a small bolt.