I can't answer the question about why Yashicas work with "non-MM" lenses in P mode.... but I can pass on what I was told by the Contax UK Manager a few years ago when he visited our Contax Postal Club's annual "Weekend away".
He said that MM lenses (like others in the forum have mentioned) have redesigned lighter blades and a less powerful stop-down spring. This is to enable the MM mode cameras to accurately select an aperture mid-way between full open and the preset aperture. The lower inertia of the lighter blades reduce the time required to close down and prevent either "sluggishness or "overshoot" by the blades.
AE lenses may work after a fashion on all MM mode capable cameras, i.e some may work satisfactorilyor even excellently, others may not. He stressed that Zeiss could not guarantee that all AE lenses would work...hence the redesign to MM's. It's not a case of damage being involved, afterall, it's the same lever mechanism in the camera that actuates the stop-down mechanism on the lens, regardless of whether you have the AE lenses mounted or the MM lenses mounted. The cameras are designed to work with both AE and MM lenses, without damage. It's more a case of Contax/Zeiss's reputation for accurate exposure that was at stake!
When one or two of the Club members ask our guest Contax Manager about putting bits of matchsticks or plastic (etc.) to hold the camera body MM lever open to fool the camera that it had an MM lens on it, he politely told us "At your own risk"!
I remember asking the UK Contax Service Manager, a few months later, about the matchstick ploy and he smiled and said something along the lines of "Yup....it has, and will, keep our department in business for years removing the bits from inside the body and fixing the jammed mechanisms!"
At another Club meeting a year or so later, I had a chance to ask the Tamron Rep about a rumoured MM Adaptall II mount. It was relatively new and, at that time, not available to the general public. He let me have a play with one and explained that the reason they were not on sale yet, is that there was a small question of reliable operation with ALL Tamron lenses. The vast majority of Tamron lenses were working excellently with the MM mount adapter, but a few gave slightly inconsistent results....hence the reservations at that time. My own experience confirms this....but, in general I have no problems with Tamron's with the MM Adaptall II.
Hope this helps and I will attempt to find out about the Yashica-AE in P mode question.
Cheers, Bob.
He said that MM lenses (like others in the forum have mentioned) have redesigned lighter blades and a less powerful stop-down spring. This is to enable the MM mode cameras to accurately select an aperture mid-way between full open and the preset aperture. The lower inertia of the lighter blades reduce the time required to close down and prevent either "sluggishness or "overshoot" by the blades.
AE lenses may work after a fashion on all MM mode capable cameras, i.e some may work satisfactorilyor even excellently, others may not. He stressed that Zeiss could not guarantee that all AE lenses would work...hence the redesign to MM's. It's not a case of damage being involved, afterall, it's the same lever mechanism in the camera that actuates the stop-down mechanism on the lens, regardless of whether you have the AE lenses mounted or the MM lenses mounted. The cameras are designed to work with both AE and MM lenses, without damage. It's more a case of Contax/Zeiss's reputation for accurate exposure that was at stake!
When one or two of the Club members ask our guest Contax Manager about putting bits of matchsticks or plastic (etc.) to hold the camera body MM lever open to fool the camera that it had an MM lens on it, he politely told us "At your own risk"!
I remember asking the UK Contax Service Manager, a few months later, about the matchstick ploy and he smiled and said something along the lines of "Yup....it has, and will, keep our department in business for years removing the bits from inside the body and fixing the jammed mechanisms!"
At another Club meeting a year or so later, I had a chance to ask the Tamron Rep about a rumoured MM Adaptall II mount. It was relatively new and, at that time, not available to the general public. He let me have a play with one and explained that the reason they were not on sale yet, is that there was a small question of reliable operation with ALL Tamron lenses. The vast majority of Tamron lenses were working excellently with the MM mount adapter, but a few gave slightly inconsistent results....hence the reservations at that time. My own experience confirms this....but, in general I have no problems with Tamron's with the MM Adaptall II.
Hope this helps and I will attempt to find out about the Yashica-AE in P mode question.
Cheers, Bob.