I got this interesting lens a few month ago for small money from an old photograper.

It is an Emil Busch 20cm (8") Quarzlinse (quartz glass lens)
It has two star shape apertures with the old German aperture values f/6.3 and f/9.0
Without the apertures it has a speed of f/4.5

Also a Filter adapter (?) for A51mm filters and a Carl Zeiss yellow filter comes with it and a blue filter rom AGFA as well.

I tested the glass and it is real a quartz glass lens element and the focus is 200mm.
Mounted in the rear thread of a Compund III shutter.

The shape of the aperture speaks for a portrait and landscape lens, a softfocus lens like the Oskar Zwierzina Plasticca lens but with the differents of the front aperture and the special glass.

I know, after reading the book from Michael Neumueller, that the star shape apertures are the best choice for single glass elements lenses and I realised it for my 270mm quartz glass lens too.

Also I know that the Hanover Company made a quartz glass softfocus lens in the 1920th, the Kalosat lens.
Carl Struss offered hin softfocus lens with optional quartz glass.

This kind of glass makes sense when you work with wet or dry plates which are only sensitive for blue and ultraviolet lights.
With ortho and pan material this glass gives a special kind of softness.
With yellow filter it can be use only with ortho- and panchromatic material.
The blue filter with blue light sensitive plates and films only, I guess.

I tested it only on the ground glass and it has a very nice rendering and I canŽt await to see the first samples taken with it.