But...

First things first.

First, here's a series of pics of the lens and cell. The cell appears custom made, but it seems like a decent machine job. The lens doesn't move in the cell by much at all. I set it on top of a plastic sourcream tub (or whatever it was) so I could lower the cell from the lens as you see in the pic after I took out the retaining ring.

There are a few small chips out of the edge of the lens. Most of these are covered by the retaining ring, but the one you see that's been marker'd out in black is about 1/2" into the field from the retaining ring.

The cell is unpainted, so the main reason I took it apart was to squirt some flat black on it to help cut down reflections off that shiny aluminum.

But when I got it apart, I noted the two "3"s printed on it, with arrows. These aren't in line and aren't pointing in the same direction. The guy who gave me the lens/cell about 5 years ago has passed away, so I don't know whether it was assembled incorrectly, or if this alignment is a result of some testing!

And finally, as I design a means of holding it in the plywood tube I'm about to make, which way is the sky? Both outer surfaces are convex, but the lens on top in the picture is thinner at the edge than the other. I presume that this is the biconvex element that goes skyward, but if someone knows different, by all means tell me!

The spacers between lenses are tape of some kind. The two lenses are stuck together with them. Otherwise, I'd gently lift the top element off and determine this for myself. Probably, I'll have to do that anyway, if the lenses aren't aligned properly here.

Anyway, first pic. Next, I'll go back outside and double check the FL before I cut any wood.

-Tim.