My M50mm f2 is basically a lens cap for my MX but I had it out so I decided to reverse the front element for some swirly effect. It was extremely soft till about f5.6. Many of the photos made me feel nauseous. With a strong center subject it could give some novel results. It was easy enough to reverse. unscrew the name ring and front element then flip and hold in place by rescrewing on the name ring.

[BigMackCam]

Fun experiment I particularly like the cat shot.

This is quite a common "mod" with various lenses... I intended to try it out with one of my late model MIR-1B 2.8/37 (which isn't nearly so good optically as my two earlier MIR-1 versions), but haven't got round to it yet. Another project for a rainy day

[swanlefitte]

I heard about it from hellios lenses. I might try it on a 105 nikkor that is broken anyway if I can find the mount, fix the dent so I can thread the nameplate on it.