BH2 Parfocality issues - NFK 2.5x Element Orientation?

[josmann]

Hey folks,

I just got in my first trinocular head for my BHTU. It's a SWTR30 with the viewing optics in pretty nasty shape but the beamsplitter path looks solid. I've got a binocular superwide that works well enough which I'm planning to combine with the trinoc to make one working SWTR30.

Despite the poor shape of the trinoc's viewing optics (some sort of liquid creep in between prisms and whatnot), I can still form an image through the SWHK eyepieces and if I swap between the trinoc and the binoc, I stay roughly in focus for roughly the same eyepiece height so I'm pretty sure there's nothing too weird going on with the optical path length.

However, when I pop my 2.5x NFK into the trinoc port, I cannot form an image of the correct position or diameter. I get an image that appears a few inches above the photo piece and is significantly less than an inch in diameter. In order to get an image projected anywhere close to where an image sensor ought to be, I have to bring the objective way too close to the slide and the eyepieces have to be held way out of the tubes to get an image there.

I have a suspicion that something is wrong with my photo piece. I bought it on eBay recently and there were definite signs of tampering with the internal retaining ring - the spanner notches were chewed up and bits of aluminum were loose inside. There was also a faint rattle upon shaking which I believe is the spacer not seating correctly. I'm wondering if some intrepid, but misguided microscopist may have reassembled this incorrectly (or, hopefully not, swapped out elements). The internal elements are laid out in the attached photo. The primary lens in the long tube does not appear to have been tampered with. The rear lens group contains a thick meniscus lens, a spacer with a small OD step, and a biconvex doublet with an OD step. Can anybody tell me if these appear to be the correct elements and what order and orientation they should have?

I asked the seller about a separate issue and they said that this was from a part-out so they have no info on it.

DSC07737-sm.JPG (76.13 KiB) Viewed 1085 times

[josmann]

A potential breakthrough!

Shortly after looking at the photo I took, I noticed that the retaining ring meshes pretty nicely with the OD step on the doublet. When I first opened this thing, the first element under the retaining ring was the meniscus lens (concave side) and I just sort of assumed that must be right. However, if I drop in the meniscus first and then the spacer and then the doublet and clamp the retaining ring down onto the doublet flat, I'm starting to get a much, much more promising image at the camera.

So now I just need to confirm the orientation of the meniscus lens and the spacer. I'm pretty sure the meniscus lens should be oriented with the convex side facing the camera based on photos. The spacer I have no idea, though I'm not certain how much it'll matter. If there is a correct orientation it'll probably be hard to tell. Any help here from somebody who knows (or doesn't mind disassembling theirs to check) would be appreciated.