but the design internally is more like a singlet and doublet. like a kellner. but backwards. The doublet is facing the objective. and the eye-lens singlet is facing the eye.
The more convex side of both the singlet and doublet are on the inside.
The singlet is only completely flat on the eye-lens side so its plano-convex
and the doublet is slightly convex on the side facing the telescope objective.
Eye relief is low but not too low. Need to get uncomfortably close to see the full field of view. eyelashes occasionally touching parts of the edge/rim around the eyepiece. though I might just have spectacularly long eyelashes.
Had to replace the rubber eye-guard because it was disintegrating and falling apart. and a disassembly and clean of the inner lens surfaces (Grimy and some spots visible inside) now its clean enough to be usable at least.
Field of view is not too bad. average. its decent. maybe 50-60
Field sharpness is lacking at the edges.. Not great at the edges. though I dont see any additional
Only see
Here are some pictures of it. Any idea what this mystery eyepiece is supposed to be And its best use cases? Its DEFINITELY not a plossl. and DEFINITELY not 17mm.