Kodachromeguy
Subscriber
At the risk of adding even more complexity into the choice of lens for a thread-mount camera, the Soviet 50mm ƒ/2 Jupiter-8 is compact and shorter than normal 6-element Gauss-type lenses. The Jupiter is a Sonnar design, so it has a somewhat different "look" than a Gauss lens. I really like mine, a coated unit from 1962. It barely intrudes into the finder view. Brian Sweeney adjusted mine to be correct for most focus distances on my IIIC. A few years ago, these Jupiters were inexpensive. Brian warned that many of the recent ones that ship from the Eastern European countries are damaged or poor hacked examples, but I have no personal experience. Some examples:
https://worldofdecay.blogspot.com/2021/07/optical-treasure-1960s-jupiter-8-lens.html
https://worldofdecay.blogspot.com/2021/07/optical-treasure-1960s-jupiter-8-lens.html