The MS Optics 50mm 1.1 Sonnetar is very fast, noted on the description sheet as being f1.16.
Now the MS Optics ISM 50mm 1.0 is available in M mount at only 178 grams.
It is noted as f1.05 on the description. So it is only somewhat faster than the Sonnetar.
If one already has a Sonnetar 50mm, not sure if they would be interested in this lens.
With Gauss type lens it does not have the soonar qualities of the former, but apparently also not the tricky coma adjustment ring.
16 rounded aperture blades.
Looks interesting though for digital or film, https://www.japancamerahunter.com/20...f-1-0-m-mount/