Focal plane distortion

just had a thought--to slow down the shutter scan speed with small slit, you can use the slowest, largest slit, but use black tape to make that slit teeny tiny---so there is less tension when it rolls down and it rolls slower than if you cranked it up to the narrow slits at the end of the shutter curtain--so make your own "narrow slit" using the big slow speed slit---use on lowest tension---that will work best on this effect I'm thinking for repeatablilty.