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"Lens, Cosina 55mm f2.8 M42 Mount"
In an era where lenses of this focal length were commonly up to two stops faster, when film speeds were low and every stop was precious... WHY? What exactly did they get in exchange for this compromise?
Of course the same thing applies even more to the Industar 50/3.5. The gain there is its remarkable compactness, but it comes at the expense of both speed and handling (it's a very fiddly lens to use, as those who have it know only too well).
The Takumar 50/4.0 macro is similar, but that was optimised as a flat field copy lens to be used from a stand, where the camera is rigidly held, remotely triggered, lighting can be optimised, and considerations of camera shake and shutter speed are irrelevant.