How many retaining rings do you need for this? Because the spec sheet of the 2" tube says that one ring comes with it, so then buying two more would actually total 3, which wouldn't be very useful, since you pretty much need them in pairs, right? It was my understanding that inside the tube it would be:

Ring-GG-ring-{16mm space or so}-ring-condenser-ring

Right? So then I would need to order three?

Joel, when I built this adapter, the condenser works absolutely great right up against the ground glass--meaning you only have to buy one extra retaining ring.

On that note, I must add that I have a FL=70mm PCXL (the same used in richard mellor's design) that I got from Optosigma available for sale, in great condition, as well as a retaining ring. If you're interested I'll sell you both a retaining ring and the PCX for $30. Let me know.

Thanks for the offer Ben, but I've decided to go with an aspheric PCX for my model and see how that compares to other people's standard PCXs. If you just want to sell the ring, I'd take it off your hands, but I understand if you'd rather sell them together. Email me if you're interested.

Sounds good Joel. By the way, if you really want to, just take apart a 52mm UV filter; you'll find a "retaining ring" in there :)

You have one ring with the tube and have to buy three extra, two for gg and two for pcx-lens.