KMZ designed, awarded russian tele photo lens with M39 and M42 screw.
First Jupiter21 was made in 1957 by KMZ (Krasnogor Mechanical Factory).
Maximum aperture: 1:4.
Focal Length, mm: 200.
Optical construction : 4 lenses, 3groups.
Minimum focus distance: 2,5m.
Mount: screw M39x1.
Filter size: 56mm x 0,5mm.
Angle of View: 12°.
Made for film: 24x36mm.
Rezolution (lines per mm) center/border: 40/30mm.
Koef. of light: 0,80.
Lenght with both cups: 160mm.
Dimensions mm (Diameter x Length): 63x160.
Weight: 690 grams.
In 1960 Jupiter21 was awarded by "Diploma I step of Air Forces of USSR".
In 1968 KMZ made new Jupiter21A version.
Lense has fully-auto aperiture with adapter for screw M42 and M39.
Optical construction stay same, but many changes:
Integrated hood.
New minimum focus distance: 1,7m.
Mounts: M39x1 or M42x1.
Filter size: 58x0,75
Rezolution (lines per mm) center/border: 50/36mm.
Koef. of light: 0,82.
Dimensions mm (Diameter x Length): 66x160.
Weight: 740 grams.
Jupiter 21M was designed in 1973 by KMZ, but from ~1980 made in Vologda by VOMZ.
Was known several models: Jupiter 21M, Jupiter21m-2 ...
New changes:
Mount: M42x1.
Aperiture: jumping with "A"/"M" function.
Minimum focus distance: 1,80m.
Dimensions, (Diameter x Length): 78x165.
Weight: 980 grams.
http://www.zenitcamera.com/archive/lenses/jupiter-21.html http://www.mflenses.com/jupiter-21m-m42-mc-lens-review-2.html https://www.pentaxforums.com/userreviews/jupiter-21m-200mm-f4-0.html 
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