Sankor made 1960's preset t-mount lens. Can be found as very similar looking f2.8 (pic 3) and f3.5 variants so both listed here. Pics 1 and 2 are of f3.5 zebra version, "SERIES E" nameplate.
Marketed by numerous names, most long defunct (Series E, Harmony, Accura, Hakunor, Mayfair, Samuron ...... ). Pic 4 by Nordentro on
mflenses shows other variants (and the 105mm).
Optics: looks like 3 elements in 3 groups (though large middle element could be eg doublet). Looks uncoated.
Aperture: f3.5 to f22, single stop clicks.
Iris: 14 blades
Focus: ~ 340 deg, pentax rotation.
Close focus: 1.7m/5.7'
Filter: 46mm.
Length (min/max): 77mm/90mm without mount.
Max diameter: ~ 53mm
Weight: ~ 330g
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