This is a beautiful example of an uncoated Summitar. NICE. Note the older aperture scale that extends to ƒ/12.5. I use a 1949 coated Summitar with the modern scale that closes to ƒ/16. The Leica Schule used to teach that below 1/4 of the focal length, you began to see degradation from diffraction. For a 50mm lens, that would be ƒ/12.5.
Some of the 50mm ƒ/3.5 Elmars closed to ƒ/22. Those may be the so-called Red-scale models.
Later macro lenses from Pentax, Nikon, etc., offered ƒ/32 for greater depth of field, but that was their main emphasis for photography of miniature subjects.