I started using the Canon 8-15 on my OM-1 using the metabones adapter and using the zoom control on the N85-N120 adapter with Wolfgang's adapter for the Nauticam zoom gear a while back now.  It all works quite well, but I was never that happy using the zoom knob on the N85-N120 adapter, it always felt coggy and a little awkward to use, plus mine seemed to need inward pressure to avoid disengaging the gears.

 

So looking at the housing and doing some measuring it seemed that I could get a 3D printed gear that would use the the housing zoom control.  I adapted a file for a an N85 zoom gear and played around with a CAD program to get roughly where I needed things and contacted member Ross Gudgeon who does 3D printing (  @Gudge ) to ask his help fixing up the rather rough and printing a gear.  On the second iteration I have one that works quite well.It takes a little fiddling getting mounted correctly but it's easy enough to do.

 

There are tight clearances and a need to accommodate the lens release and the jog lever on the Metabones and the projecting "viewfinder" hump on the OM-1.  I ended up grinding down the jog lever a touch as it was contacting the inside of the gear.  End result a zoom gear that works nice and smoothly from the housing control knob.

 

Some pics:

 

You can see how tight it is getting the gear in place here:

 

 

Tight clearance to the camera body:

 

 

Thanks to Ross for helping out on this project!

Here's the STL file for anyone who wants to print it.  You'll need a 16 x 3mm socket head screw and 3mm nyloc nut to attach it to the lens.

Olympus - Canon 8-15.stl

Thank you!!

Added to our DIYpedia: https://waterpixels.net/forums/topic/671-proven-3d-printed-parts-for-underwater-imaging/

 

Thanks 

 

 

 

Tried it out in the water a few days ago, and it worked seamlessly, zooming was as smooth as with a Nauticam gear on my 12-40mm.