This is an ABS pipe fitting. ABS is like PVC only it is made of black plastic. The great part is these babies only cost 79 cents. It is almost perfect for holding a 40x80 ES lens. The height would have to be sanded down to the correct edge thickness and you may want to cut off the threads. It comes with a white plastic retaining nut with a pressure ring. The nut could be cut so it would tighten all the way up to the flange. Also, to take advantage of larger diameter lenses, the smaller ID would have to be turned a little bigger, from 32.1 mm to say, 38 mm. This would leave a 1 mm flange all around the inside. The minimum ID being small is good because it can be used to accommodate many other smaller lenses. These would have to be shimmed or sleeved to tighten up the extra space of the larger 40mm ID.
This lens mounting ring is designed to accommodate a 40x80mm achromatic lens from Edmund Scientific (45105, $73.90 each). This presentation is for your review only. Rough dimensions were borrowed from John Bercovitz's lens holder design. The construction material is hard plastic which explains why the design is slightly more robust than an aluminum or brass version. One innovation in this design is the missing fourth mounting hole. Three mounting screws should do the job, the fourth is left out for a nose relief. The orientation of the mounting ring in the drawing is only to make the "section view" easier to understand. It is intended that the ring would be square with the world when attached to a viewer.
I did some prototype work with a plastic molder a few years ago and gave them a call to see what they would charge to produce a limited run of these mounting rings. The cost would be about $12.00 to $15.00 a pair for a first run of 50 pieces. This seems to be within the range most of us were thinking. Since there are fixed setup costs, the more we get, the more the price each goes down. If we could get an initial order of 25 pairs, we could see how they work out and make modifications for the next time around. To make the first pair would cost about $65.00 if we didn't want to jump in with both feet right off. This is not an exact science when dealing with the plastic. There is an unpredictable degree of shrinkage in the molded material so we could have to produce the prototype several times to get it just right. It seems the only critical dimension is the inside diameter (as long as the barrel OD is sufficient to allow for multiple retoolings). I will volunteer to do the prototype production on my own lathe and all modifications. This saves us half the setup cost which is normally about $100.
So others can participate, direct all comments to the list:
It might not hurt to cite this page's address when sending in comments. I read the medium format digest and I will incorporate changes to this page.The light gray rectangle in the cross-section is the lens. The drawing is to scale with the lens diameter at 40mm.