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By the mid-1970s, the advantages of bayonet lens mounts with open-aperture metering were clear; and even Pentax had moved on from the M42 screw mount. The Cosina CSR and its siblings the CSL and CSM from Cosina circa 1976 were interesting late attempts to keep screw-mount SLRs viable.
A half-press on the shutter release stops down the lens for metering, with over/correct/under indicated with LEDs at the top of the viewfinder. The lens can be reopened to its brightest aperture again with a button on the camera front.
The CSR is distinguished from its near-twin the CSL by allowing the user to switch between averaging and spot metering (in this, it resembles a Mamiya/Sekor DTL model). The CSR was made in both black and silver versions.
The electronically-timed shutter ranges from 1/1000 to 4 seconds, with flash sync at 1/60th or slower; but without power from two 1.5 volt silver-oxide batteries, only a mechanical "M" speed of 1/50 second will function. There is an electronic self-timer with a small LED which blinks during countdown. A tab alongside the wind lever allows for multiple exposures.
The most notable (and heroically misguided) feature offered with Cosina's "CS" SLRs was the optional AEC adapter box which attaches to the top and provides autoexposure via motorized rotation of the shutter speed dial.