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You ca try it both ways. It will have similar results. On the back it looks a loot neater but at the same time you cant adjust it during shooting

well it looks easier to put it on front, or even to put it behind the front lens on helios 44. interesting :)
and you have to have in the mind the aspect ratio, maybe magiclantern has it.

I wouldn't kniw about magic latern. Im on nikon