As EdSawyer has stated, your problem was using a round hood instead of a square one. Just one word of caution in buying the second hand Mamiya square hood made for the 50/65 lenses - try to ensure that the rubber has not sagged too much - so many of these hoods suffer from serious bowing, such that the straight edges of the square bow inwards towards the glass. If you use a deep filter, it can be enough on the 50mm lens to cause some minor vignetting. I'm sure there's a technique for curing this tendency in these hoods but I've not been able to find one thats reasonably permanent.