You must use a circular polarizer with the F-1, F-1n, New F-1, FT, FTb, and any Canon that has the partial area metering block in the viewfinder screen. That block has a beam splitter mirror that diverts x-amount of light to the meter cell which is in the body. The beam splitter mirror will go black when a linear polarizer is used because the mirror acts as a phase polarizer. This was a very common problem with the early autofocus systems that used 1/2 mirrors (beam-splitters). This problem is avoided with a circular polarizer.