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M 50/2

General Description

Product Information
Exact Namesmc PENTAX-M 1:2 50mm
Years of Production1979 ~ 1985
Availabilityused, several times a month
Catalog Number20677
Sold with Hood
Sold with Case

Technical Specifications

Optical Formula5 elements in 5 groups
Aperture Rangef/2 ~ f/22
Number of Aperture Blades6
Minimum Focusing Distance0.45 m
Maximum Magnification0.15 X
Filter Diameter49 mm
Maximum Diameter63 mm
Length31 mm
Weight160 g
Capplastic clip-on cap, 49 mm
Fitting Hood(s)screw-on hood: PH-R49
clip-on hood: PH-S49
screw-on hood: RH-R49
Fitting Case(s)dedicated hard case: exact name unknown

Subjective Evaluation

This lens is not very exciting. It was the standard lens that Pentax sold with all their M-series bodies, so it is very abundant. The lens was optimized for low-cost production and is optically not quite as good as the slightly more expensive M50/1.7 or A 50/1.7. Still, if you've never used a prime lens, you will be amazed at the quality of images you get with one of these "cheap lenses".

However, there is one interesting thing about the M 50/2. In early 2007 Fabio Cittadini noticed that some M 50/2 lenses featured a linear aperture lever — just like the newer SMC-A lenses. Fabio Cittadini and Dario Bonazza were able to track down several M 50/2 and compiled the following list of differences:

  Early Lens Late Lens
Example Srial Numbers 4327532, 4455263 4991229, 4991994, 5838189
Diapfragm actuator displacement proportional to aperutre diameter aperture area
Lettering on front ring ASAHI OPTICAL CO. ASAHI OPT. CO., JAPAN
Lettering on lower side of aperture ring MADE IN TAIWAN none
Lettering on front cap ASAHI PENTAX PENTAX
Weight 165 gram 138 gram
Aperture ring 49 teeth 59 teeth
Aperture-blades ends visible from back visible from front
Rear barrel details fixed/moving 3/5 rings 5/3 rings
Aperture simulator chrome black
locking notch U-shaped elliptical
We could assume that Pentax ran out of parts for the old-type M 50/2 lens and when they needed a new batch of lenses, they simply used parts from the newly developed A 50/2 lens and a mount without lens contacts. There is one more example of this practice — the M 28/2.8 lens.