Hi all,
there was a thread on Photo.net a little while ago and also here (I
think) about the possibilty of adapting a 500/4.5 to medium format. The
removable mount tube has made it relatively easy to convert to other 35mm
mounts, so the idea of making a MF mount seems obvious. In comparison to the
price of a "proper" MF 500 these are an absolute bargain and seem to come up
on Ebay at least once a month, so you can understand why the idea is
attractive.
I'm on holidays at the moment and have a bit of spare time so I thought I
would see whether it was feasible. As I also have the 500/5, which is a much
simpler design I though I would try that too. I set the lens up on a tripod
and set the focus to infinity. I then set up my speedgraphic on another
tripod, with a piece of cardboard replacing the lensboard. The cardboard was
cut to be a snug fit around the rear barrel of the lens, once the lens mount
tube had been removed.
With the 500/4.5 the image circle on the ground glass was around 65mm in
diameter at the biggest, which is too small to even cover 645. There really
wasn't much in the way of variation on this figure regardless of aperture.
The main reason for this appears to be a retsrictor baffle that sits in the
focussing helicoid. Removing the baffle may increase the image circle but I
wasn't about to try. In any case, it would mean that any conversion would be
a permanent one, rather than simply replacing the mount tube with one
engineered for 645 or 6x6.
When I tried it with the 500/5 I was able to get a larger image circle,
75mm, but that is still too small for MF. In the case of the 500/5 the lens
is a lot slimmer at the rear than the 500/4.5 so there doesn't appear to be
any way of improving that figure.
Theoretically some sort of low power teleconverter could be used that would
give a larger image circle, but that is starting to get expensive. So all in
all, it looks like the 500/4.5 is only good for 35mm.
Paul Ewins
Melbourne, Australia
