Mamiya 7 80mm Lens: Rangefinder Cam Far Out of Spec
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
The complaint on this Mamiya 7 w/80mm lens body/lens combination is that the images are not sharp. But, the rangefinder lined up perfectly.
A quick exam showed that the rangefinder cam on the lens was almost fully retracted in the lens barrel when focus was set at one meter. Photo two show the lens in question compared to a calibrated lens on the right. Very large difference in the cam location. But, how can the body rangefinder show correct focus?
Turns out that the body rangefinder had been adjusted to match a very far out of spec lens. So, the rangefinder split would show as correct but in fact it was very off. This is why you check and adjust the lens rangefinder cam first before adjusting the body if you are using the lens as a reference (I don’t use the lens as reference as I have a factory standard but I realize not everyone is going to have this part)
In this case, the lens was about as far off as I have ever seen. The video in photo 3 shows how the lens did not even start to connect with the cam until the focus was set at around 30 feet. And then it was off by 115 divisions (1.15mm!) as the dial had not gone around yet fully.
On top of this, oil of some sort had been squirted into the back of the lens to try to fix the shutter cocking lever assembly in the rangefinder cam. Photo four shows the rangefinder cam assembly being removed and visible in photo five is residue from the attempted repair show as stains.
After all was cleaned and recalibrated, the lens now works to specs as shown in photo six. Of course the body needed to be calibrated also as it was very far out to try to adjust to this carelessly serviced lens.
