• Tom Page of Wickford Camera Repairs, at that time located in London, my regular Pentacon Six repairer, who is great at stripping down and assembling lenses
• Ian Broomhead of SRB (formerly located in Luton and now relocated to Dunstable), who are experts at making custom filter rings and other adapters

The lens is in two parts: the front component, which was screwed into the front of the Compur shutter/aperture unit, and the rear component of three small elements behind it.
 

I was clearly tilting the camera up in this hand-held shot, hence the inevitable converging verticals, but the lamp post near the edge of the frame is absolutely straight – much better than the results with Arsenal’s 45mm Mir 26B lens!

With these excellent results, it was worth taking the project further.  I bought an 80mm Exakta lens in Exakta 66 mount from Niclas Walser, and Tom Page removed all the elements for me.  (You can see what happened to those spare elements here, fairly near to the bottom of the page.)

SRB made a collar that locked onto the front component of the Curtagon and screwed into the filter thread of the empty Exakta lens barrel.  It was harder work to design a tiny tube to hold the rear 3 elements at the correct separation from each other and attach them behind the aperture that was in the Exakta lens, but they made a little tube and Tom assembled all the bits.
 

Then by seeing how other Schneider lenses mated with the Exakta 66 metering prism we were even able to add a pin to tell the meter that the maximum aperture was f/4.

Naturally, rotating the aperture ring also tells the metering prism which f/ stop has been chosen.

Here’s the finished product.

Of course, two things on this mount are wrong: the focussing scale and the depth of field scale.  However, with the bright Rollei focussing screen in my Exakta 66 and Pentacon Six cameras, focussing is not a problem, and of course with a lens of this focal length, the depth of field is considerable at most working apertures.