Hi Thomas, A circular polariser is a linear polarisering film with a special glass behind it to rotate the polarised light. I am using a linear polariser with my F3 and I had no exposure problems. I think the mirror in the F3 is different to the mirror in the AF cameras. The F3 mirror has many visbile tiny perporated holes to let the light through to the secondary mirror, so that the rays of light are not so much affected. I think the perporations on the AF mirror are much smaller, so they do affect the polarisation of the light rays. Maybe someone else can clarfiy this or correct me. Hope this helps, Sover
