For everyone's benefit, adding a detailed response from Bob from a reddit thread that I posted on the same subject.
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This is Bob Sara, Yashica Company Trained TLR Technician, still servicing these cameras after 40 years.
The rear taking lens us a grouped element. There is flat side and a Convex side. The flat side should always be facing the backside of the shutter aperture and the convex side should be facing you when you open the film bay. To verify whether it is installed correctly, simply wrap a thin layer of lens tissue around your middle finger and run it slowly over the lens side to side. If you can feel the curvature of the lens, then it is installed correctly. Since the grouped element sits within a millimeter or so from the back of the shutter aperture, should the lens be installed in reverse, the convex side would have interfered with the easy movement of aperture blades and would have also consequently scratched up the convex side of the lens. This is what had happened to a recent Yashica Mat-EM I received for service when the owner had tried to clean and re-install their own rear element.
However, if the lens is installed correctly, you still want to verify the clear condition of all taking elements by looking thru the entire taking lens set from the back of the film bay. Simply reset shutter and hold-in the release (release cable with a lock would make it easier) and look at the entire lens set while refracting (at an angle) a bright light while looking for anomalies like haze/fog (looks like heavy dust or fone lube splatters), or lens fungus(looks like patchy cobwebs). or lens separation (looks like either little bubble and/or areas of discolored or cloudy glass). Lens fungus and balsam separation are common for these old cameras.
Once you verified the correct orientation of the rear grouped element and verified that your entire taking lens set is Crystal Clear, now by process of elimination you can move forward to checking the other possible causes.
Other causes could include: A- A mismatch of taking lens elements if someone swapped just one affected element without changing the entire lens set or if they swapped an element with one from an incompatible model. In All TLRs, Including in Rollei, you must change all taking or all viewing lenses together at once! This is because No two front or rear elements were manufactured identically and the factory had to match all elements and calibrate them together on each camera in order to achieve the 75mm or 80mm focal length.
B- If camera focus mechanism were not re-calibrated after swapping any lenses. C- If the camera experienced an impact and if that caused any deflections in the position of the lens plate or focusing arms
To Solve the issue you have to test one thing at a time and by "process of elimination".
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Visit my facebook page(link below) to see how these cameras are serviced and maintained.
https://www.facebook.com/yashicarepaircenter
For questions or service inquiries, please email to:
CLAStudios@Msn.com
Still would be great to have correct. Those are great cameras. Maybe someone made a soft focus adjustment?
