©Lin Yangchen

special part designation

cad file download
personal non-commercial use only
use at your own risk

When I switched to UIS objectives on my Olympus BHSP, I engineered a modified dovetail mount to accept the 25 mm PE projection eyepiece.

Constructive solid geometry in FreeCAD, with stacked cylinders for the main body, chamfering to make the dovetail and set operations on nested cylinders to excavate the central shaft and weight-saving cavities.

Precise positioning of screw holes with angle and radius constraints, and extrusion of 2D geometry to form the shafts.

Crossbeams added. Cutaway shows the interior architecture of an ancient shrine for communicating with the gods.

The cavities are suboptimal from a design-for-manufacturability standpoint and can be filled in if weight is not a limiting factor. Blue regions indicate material that cannot be removed. Simulation by Proto Labs.

The original 23 mm-calibre dovetail mount (right) and the 25 mm high-calibre “military spec” steel version machined with lathe cutting and computer numerical controlled triple-axis milling at a tolerance of ± 50 μm, followed by deburring and a high-impact-and-corrosion-resistant quench-polish-quench black oxide finish (left) on austenitic stainless steel grade 304. A layer of iron nitride was first formed by diffusing nitrogen into the alloy at temperatures in excess of 500°C. This was followed by polishing and a salt bath to deposit iron oxide (Fe3O4). Most of the edges have been left unchamfered to preserve the raw machined look. In true military tradition, it weighs three times the regular version (335 g versus 115 g).

The final step was the hardest—sanding down the eyepiece to fit. I had taken a calculated risk and proceeded with the machining of the dovetail mount before I had the eyepiece, allowing enough clearance for the documented eyepiece tube diameter of 24.8 mm. But when the eyepiece finally came in the mail, I found that the tube began with the correct diameter but fattened to about 25.1 mm the rest of the way. So here's a Brushed Silver Special Edition PE projection eyepiece.
Powered by SmugMug Owner Log In