The FD 17mm lens Jeff is a semi-fisheye that produces curvo-linear perspective which is why I bought the FD 20mm f2.8 as an ultra wide lens in preferance , the Tamron SP is also a recto-linear lens that produces more conventional ultra wide angle images .
Are you sure? I'm pretty sure the 17mm is a normal rectilinear super wide angle lens. That said, I never owned one myself, just the 20mm.
I believe you are thinking of the 15mm rectangular fisheye lens.