Based historically on the classic 1896 P. Rudolph design from Zeiss Stiftung, Two very early, turn of the century Planar antecedants (circa 11/14/1896. On sale in Sweden November 1896) are shown below:

Despite the years that have intervened and the history of progress there is a very strong familial resemblance between the the Rudolf/Stiftung designs and the modern updated designs giving testimony as to how amazingly advanced these were for their time.
The modern day Planar is one of the very best 50mm (actually it is really a 51.8mm) f1.4 lens executions ever achieved.
This 7/6 embodiment employing the most modern glass reformulations, the very latest in multicoating technology and highly refined and optimized glass element curvatures has resulted in the achievement of apparent sharpness, distortion freedom and color saturation capabilities unexcelled by any other f1.4 "normal" offering in the marketplace.

This lens is truly an historic classic updated into a modern day extraordinarily fine classic lens and strongly resembles the very modern updated embodiment shown below:

The pre MM mount, without the GREEN color minimum aperture coloring and without the camera body enabling coupling:

is only capable of aperture priority automation though it is optically identical.