Sure? May I recommend this article on the history of the planar?
http://vintage-camera-lenses.com/carl-zeiss-planar-history-part-1/
check out the cemented surface of the third group in the planar for the 1953 Contarex, it looks pretty flat to me.
http://www.marcocavina.com/articoli_fotografici/Zeiss_Planar_50mm_story/00_pag.htm
The Planargon 35 mm also have four flat surfaces, and the 1955 Planar 55mm f1.4 two in the second element.
Thank you for the two links
The second compromises both our postures when/if you read the table describing the radia, refractive index and dispersion, it is apparent only one surface in each lens is planar ie has an infinite radius.
If you then look at better diagrams of the ZM it is then similarly clear that
- it also has only one planar surface set
- and it is a close analogue of the fifties cyclops design
My mistake sorry
This does not make it bad as Cosina (ie Zeiss) will have manufactured it with the year 200x glass catalogue. And it is a design with lots of freedom for correction, whereas the type IV cron with a 197x catalogue is more austere.
You will need PanF and tripod to detect any difference. I did not try that comparison.
In street shooting with each I got them both to flare (ie not just veil) distressingly frequently and I found the post 94' Elmar or Cosina /2.5 5cm a better compromise for just out of sun shots, as well more compact. Most of the time I use Canon /1.8 preferring a medium contrast lens. Note the deep optional hood for the Cosina makes a difference to flare.
But YMMV!