Mamiya 645 80mm f/1.9: Cine Conversion Warnings
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Cine converting Mamiya 645 lenses is very popular these days. As a minimum, they are de-clicked and a focus gear is installed.
Here is a warning with these conversions: make sure that your lens is in good condition before converting it.
With the Mamiya 80mm f/1.9, a popular example for conversion, the focus helicoid often has dried or sublimated grease and this will cause the focus to be stiff. I would recommend having the old grease removed and new installed before converting otherwise you may wind up with a loose focus ring and lost focus. The ring comes loose because it is only held onto the focus helicoid with three small 1.7mm setscrews (photo two shows the inner part of the barrel where the setscrew contacts the helicoid) and the extra force of moving the focus ring with stiff grease will cause the setscrews to break free. The issue with a recent copy in my shop was that the company that installed the focus gear heat shrinks it to the focus barrel so it can not be easily removed. The heat shrink makes a very durable connection and the focus ring won’t be coming loose, but the lens can not easily be repaired or focus calibrated so it is best to have it fully serviced before conversion.
The third photo, a Mamiya 645 110mm f/2.8, has been modified to Arri Pl and while the conversion is very solid, the issue is that the diaphragm does not work. On disassembly, I found that the diaphragm cam retainer was not installed and instead a large amount of grease was applied (seen in photo four), probably to keep things together without a retainer. Not a good idea and ultimately a failure. Photo five shows what the diaphragm cam looks like with a retainer installed (the diaphragm cam runs from around 3 0’clock to 5 o’clock and the retainer that is missing is shown on this example holding it in place).
