I really don't know where this lens came from, and I doubt the eBay seller did, either. Best guess is a salvaged aerial camera, but who knows? I do search eBay occasionally for aerial cameras. If a complete one every came up at a low price, I'd nab it.
What I'd like to see for myself: Did the original lens assembly correct for the field curvature? I have to think they would, but I'd like to confirm it. In Googling, I saw tons of these, and all the complete sets had additional smaller lenses in the optical train. The TN5 is missing those.
With the TN5 and Stubby (my 6" F4 Newt), I have 2 large fast grab & go scopes that the VersaGo can carry. BOTH need about the same amount of time to temperature adjust. The TN5's 3-element lens + cell is massive. Removing the 2" focuser's dust-cap helps. The TN5 is sharper overall, but both scopes are good up to about 200x. Above that, the center area at best focus & correction is small, and no fun on an alt/az!
I built the all-Mizar AR-1 + ShortPod for Stubby, so y'all know it's a Keeper. After what I saw last night, I may build a pedestal option for my VersaGo, or an all-new pedestal alt/az for the TN5. With all the dovetail hardware, I can't get to directly overhead with the VG on a tripod, and hauling out my Meade StarFinder + 5' pedestal is overkill -- defeats its portability advantage. When I'm sweeping a wide arc, I hate bumping into the tripod hub!!