Work in Progress, print at your own risk.

The design is printable with a Stereolithography (SLA) printer only. A resin or powder based one like the Form 1+ https://formlabs.com/store/us/form-1/

I started a bit of a project designing and building a retro Pi TLR camera. So far I have a the shell, lens assemblies, internal mirror for the viewing lens and body designed.

How it works:
The taking lens projects onto a 36mm ground glass square. A 8MP pi camera with a wide angle lens will then snap a picture of the projected image on the ground glass. The ground glass should produce a film grain effect that will be a physical part of the camera. The design will likely to be redesigned throughout the build. I also designed a electronics bay that will easily screw onto the back.

The camera is also quite small in size to be more portable.

Use:
Just like real TLR camera's you hold the camera at waist level and look down at the 36mm ground glass. Using the focus knob to bring the subject into focus and take a picture with the 12mm button in the front. Their is no "live" picture on a LCD or electronic display but rather a pure optical viewfinder. You will only be able to see the picture when you transfer them later or over WiFi though the Pi.

Parts List: Likely to change

Optical Edmund:
19mm Dia. x 80mm FL, Positive Meniscus Lens, Grade 1 Stock #73-931
15mm Dia. x 35mm FL, Positive Meniscus Lens, Grade 1Stock #75-023
50 x 50mm Silver, 4-6λ Mirror
Custom ordered 36mm dia 1.6mm thick 220-grit Ground Glass Diffuser
Custom ordered 36mmx36mm 1.6mm thick 220-grit Ground Glass Diffuser

McMaster-Carr:
x6 Sealtapping philips Screws, No.0 L=3/8" 1
x4 M3x4 CSK Machine Screws
x4 M3 Hex Nuts, Thin
x1 48 Pitch Rack for Plastic Gear 57655K61
x2 Nylon 24 tooth gears 57655K16

Electronics:
x1 Pi Zero-W
x1 8MP Pi Camera with Fisheye Lens
x1 Momentary Button, SPST w/ LED 12mm
x1 16GB micro SD card
x1 PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C
x1 Lithium Ion Polymer Battery - 3.7v 2500mAh