They are indeed of a plössl-like design. Nothing wrong with that, mind you, it's all in the execution.
Yes in the scope site I take from Kunama, they write Or. / PL
If this is the design sketch this could cost much.
But; if this is cheap to build for a complex formula, it may be an evolution of the "Taylor symetric cheap plössl" that was good due to glass choice.
The two doublets were made with equi-convex crown and flat plano-concave flint.
I image this as this.
Equiconvex are easy to control at short fl., so the two crown are easy to figure well : goal is null spherical aberration with source at 2fl of the lens.
Plano-concave too are easy for the flat part and then easy to match to the convex with newton ring before cementing. Flat and same radius are easy to check with this.
Then, before end, controling and finish figuring the sky concave lens. first the surface to adjust the cemented part with newton rings.
Finish is done by adjusting the eyepiece chromatism, figuring/controling the last surface.
Not bad at all to reach high optical quality. But the glass formula may be hard to find.
Maybe searching the base formula "Abbe duplet" could help.
Not Abbe duplet, more true plossl with 2 glass only.
Edited by lylver, 08 October 2019 - 06:10 PM.