How to make a K-mount mirrorless tiny

Possibly. Technically from a mirror technology standpoint there appears to be no major issue (barring mechanical interference with the upper front edge of the sensor IS housing - which I suspect is the real reason it isn't done).

But, you have to remember that the mirror now goes from being a minor component expense to a major one. The quality of the mirror would have to be approximately 0.25 wave which takes it from a about $10 component to a $60 component.

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