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Owner reviews: Pentax SMC K 135 mm f/ 2.5
Sharpness wide open
Color and contrast
500g (but balances pretty well)
No Manual-Auto switch on my copy, so the pin does not allow changing aperture on digital body w/o modifications: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/308154-asahi-smc-takumar-135mm-2-5-m42.html
I've got an earlier SMC PENTAX 1:2.5/135 version (1975-1977) as opposed to smc PENTAX 1:2.5/135 (1977-1985). Both versions are considered the sharpest wide open 135mm lense ever made with excellent color reproduction. It surpasses Super-Multi-Coated Takumar 1:2.5 135mm (M42).
135mm Lens War: http://oomz.net/135/