How I made a "free-lens" with some pond liner (howto guide).
Added aluminium foil at the back section of the DIY foamcore softbox (before the first diffuser) so as to stop so much light leakage. The main body does still leak a little, but it should be a trifling amount now.
Similar to the one on DIY Photography!
On a whim I went to Real Camera and asked if they had any old, vintage, and ideally "soft" lenses for sale. Was I about to be in for a treat!
Ross London Lens