Originally posted by pathdoc Looking at both the Takumar and K series primes, I'm struck by curiosity over why a lens maker would have two series of lenses so close in focal length.
In the M42 and SMC K series lenses (essentially the same lenses with different coatings and substitution of the bayonet mount) my 50's have softer edges and a pleasing isolation of the sharper center subject area at wide apertures, while the 55's are somewhat flatter. In a 1975
Lenses and Accessories brochure I have the K55/1.8 is described as suitable for work on a copy stand or copipod (IOW, for 'flat work'). That distinction carried over to the M and A 50/1.4's vs. 50/1.7's.
Then there is product segmentation.
The 50/2.0 lenses were supposedly identical to the 50/1.7 lenses but for the addition of a baffle at the rear element to prevent stopping down further than f/2. I've read the economic theory was, they were still profitable at the lower price, the distinction allowed charging even
more for the 50/1.7 and 50/1.4 and they made an affordable kit lens with budget bodies such as the SP500 and the K1000 (which were also virtually identical internally to the more feature-rich bodies, with some features disabled).
For instance by removing the lever for self-timer and DoF preview from the K1000, and covering the battery test button with a hump on the top plate, they turned a KX/KM into a budget camera; or by simply not marking the 1/1000 shutter speed on the SP500 (it is there,
the dial will go to 1/1000, but it isn't marked) they made a budget Spottie vs. the SPII.