Gave my vintage Diana another shot, I am not sure what's the problem here... but whatever, the resulting effect is kinda cool :p
simonesavo, ttmtk1127b, giuli, artichekt & lucretia.
Well it's leaking light massively. Good luck finding it. Have a similar problem with my Isolette
Thanks for the comment, I will try another roll, less sun, and see what happens :)