Mamiya 645 45mm C Lens: Oily Diaphragm Blades and Reassembly
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Servicing a Mamiya 45mm C lens for the 645 system. Very common issue, oil on the blades causing the diaphragm to stay open wide.
The 45mm lens (and the 35mm) is a little more complicated in design than most of the other C lenses. It has a floating element design so reassembly needs to be done carefully to maintain specifications in the focus mechanism. Also, like most lenses, when reassembly of the diaphragm is done, there is an adjustment on the plate for the correct size diaphragm opening (photo four shows a hole gage being used to insure correct size).
Photo five shows the shims used on the rear element to adjust resolution. These come in several sizes and it is important to check resolution and install these shims.
Final step is adjusting the lens focus for infinity as seen in photo six
Just thought that I would add:
When reattaching the spring for the diaphragm assembly, I use a tool that I constructed to make things a little easier. If you do much work on lenses, you might want to make tools like this to deal with springs. Photo seven shows the handle of the pin vise (on the right) that holds my spring tool which is made from a sewing needle with the top portion of the eye removed (photo eight is a close up photo of the modified needle on the right). This makes a tool for grabbing very small (1mm) spring ends.
