Why not painting with Trioplan 50 2.9 ?
Lets try it!

First some historical notes. In 1916 Meyer-Optik-Goerlitz  introduced the Lens Legend: The Trioplan. Of course, also a 50 mm lens design..
http://camera-wiki.org/wiki/Meyer
https://www.meyer-optik-goerlitz.com/en/history/

The ALTIX Trioplan

Data’s of a lens made for the camera ALTIX are shown in the following:

Optical design: 3 elements in 3 groups, 

Cooke triplet
Flange focal length: 42,5 mm
Focal length: 50mm
Aperture: 2.9- 22
Blades: 12
Min. focus: 0.6 m
Filter: 35,5 mm
Weight: 80 g
Max. length: 35 mm
Manufactured: ca. 1960
Manufacturer: Meyer Görlitz, German Democratic Republic 

https://www.dresdner-kameras.de/altix/altix-objektive/altix-objektive.html

https://petapixel.com/2016/04/14/meyer-optik-resurects-trioplan-f2-950-iconic-soap-bubble-bokeh/

The lens was adapted to a Nikon D750. Unfortunately, due to the optical back focus, only macro shots are possible. Please note, Nikon Z mount allows a perfect adapting.

Two set up were used:

A) the lens was directly mounted

B) or a teleconverter 2x (Wirgin M42)was added.

  
Let's see what we can “paint”.

Do we see a pronounced appearance of the bokeh as "soap bubble", or also other nice bokeh effects?

Dance

 A =2.9 

 
A teleconverter 2x (Wirgin M42) was added.

 GalaxyTRIO5029

A =2.9, with teleconverter 2x

 LetIt 

 A =2.9, with teleconverter 2x

 Spring

  A =2.9, with teleconverter 2x

 VERDICT

• The Trioplan 50 2.9 paints the “light bubbles” bokeh at full aperture. 
• If a teleconverter 2x is added then the soap bubble bokeh is more pronounced.
• Some people may like it, others may never like it.
• Personally, I think it's a small light weight lens to use it for creative image design.
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