Jan 21, 2012 - Rectilinear Correction? Is this called 'Rectilinear Correction'? Of this lens and they mention a software to do what they call defishing:. Canon 15mm fisheye or 17-40mm? Discussion in 'Canon EOS' started by alirezar, Jan 1, 2010. What software you use for defishing? I know DXO does a good job, but it's super expensive for just defishing. Most of the image around the centre is fairly rectilinear looking and post correction is not as difficult. Plus, the lens focuses in a.