Paul, you may not care about, or consider the registration and parallelism of the film to be of much consequence in LF, but to say that a Grafmatic doesn't rely on plastic for it's dimensional stability is just plain wrong.The whole front face of the thing is plastic, and this is the bit that mates with the camera and forms a major part of the light seal. The steel back is merely a cover screwed to that plastic, and carried by it, as anyone can see.The moveable septum carrier is made of a metal alloy, but this simply slides behind the plastic front, and that plastic front most definitely plays a large part in governing the distance of the film from the camera back. If the plastic gets warped, then that distance won't be correct, no matter how flat the septums are.
Consider that just the thickness of a sheet of film, a 0.2mm shift in focal plane, gives a 10% focusing error at 10 meters with a 150mm lens, regardless of aperture.Now, I'm measuring close to 0.5mm error in all my Grafmatics, and that's a 20% focus error.So what's the point of carefully focusing with a loupe on the GG, as most LF photographers do, when a dodgy filmholder then shifts your focus by nearly 2 metres in 10?
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