Originally Posted by rlouzan
Taking lens SN 2.986.XXX:
*Front element exhibits both a magenta and orange multi coating 'of sorts'.
*Rear element is orange-yellow, similar to the color cast of a radioactive Summicron, could be lens coating ...
However, this still doesn't explain why the rear element is completely flat, not even close to the lens cut shown in #15.
The rear element is less curved than the front element, but the reason to why it looks flat is the angle you're looking from. You can't look at it from the side when it's deep inside the camera, and it will probably also feel flat if you touch it with a finger (don't, that's unecessary!). You can cut a ca 2 cm piece of thick paper and hold it with a pair of tweezers against the lens surface and see that it's not exactly flat.
I took a picture of mine, and it does look "flat", but you can see the reflections from my lightsource that they bend a little.