Mamiya 7 pressure plate set wrong--cause of out-of-focus?

[MikeSeb]

Got my beloved Mamiya 7 back from Mamiya America today after CLA and rangefinder adjustment. Quickly loaded up a roll of 120 and went to town, testing focus at max aperture with each of my three lenses (50, 80, 150). Noticed that film advance was tougher than usual, but only when the counter didn't stop at 10 at roll's end did I notice that the pressure plate was set to 220! Guess the technician at Mamiya put it there--I've never shot 220 in this camera.

Is this alone enough to account for alterations in focus plane or lack of sharpness in all the images? It is barely there, if at all, with the 50 (a laceratingly sharp lens); perceptible as back-focus (but sharp in the "wrong" plane) with the 80; and overall unsharpness with the 150.

On one hand it makes sense--220 is thinner and has no paper backing; but OTOH, the film plane is determined by the film gate, so what should it matter?

So when I shoot a roll of 120 tomorrow with the pressure plate set correctly, will my problem be resolved or will I have to part with my beauty again for two weeks' hiatus? I'm really trying to convince myself it'll all be better with the proper pressure-plate setting!



Thanks all.

 

[Tom Stanworth]

probably will be fine. Theres only one way to find out!

 

[Pinholemaster]

No, the pressure plate position simply sets the counter for 120 verses 220.

Any focusing problems you may have with the 150 mm is do to the fact that many of those lenses were defective from the factory. I had one that never produced a sharp image. Mamiya finally replaced it, and have had no problem since.

 

[MikeSeb]

Walter, you're killin' me! I never had focus problems with the 150 before this RF adjustment. I sent it in due to a slight back-focus with the 50 and 80 (?150--used rarely) that began after the camera bounced around inside my car during a near-collision. The RF was calibrated but no other problems were found.

If it's not a pressure-plate issue then the RF adjustment must be off.

Hopefully it will be moot upon processing the 2nd test roll. I hope so--I've been beset with nagging gear issues of late and it's a distraction!

 

[ic-racer]

All 120/220 cameras I know of with adjustable pressure plates shrink the film channel depth by moving the pressure plate closer to the rails for 220 film. Under these conditions, if you shot 120 with the plate set to 220, indeed the edges of the image will be OK because the film rails are keeping the film in the correct plane, but in the center, the extra width of the paper can exaggerate the films tendency to bulge out in the middle. You will see this as having a focal point OK at the edges and too far back behind the subject at the center of the frame.

 

[MikeSeb]

Well, I've shot three test rolls through the camera since its return from service and thought I'd give you all an update. Thanks to everyone for chiming in here.

It appears that setting the pressure plate incorrectly can indeed cause a significant focus defect. That was the lion's share of the focus problem. So it appears the Mamiya folks did the proper job on the RF adjustment. But what appears to be at play now is the very narrow DOF of the longer two lenses, which I think accounts for a lot of whatever focus difficulty is left now that the pressure plate is set correctly. Since the M7 has only a 1/500 max shutter speed, with my usual films 160-400 ISO in daylight I'm rarely shooting wide open; I'm usually at f/8 or smaller.

The first two test rolls I shot at maximum aperture with all three lenses with relatively slow film; the third, at f/11-f/16 with faster film. I've concluded that, at maximum aperture, it's damn near impossible to focus the 150 accurately regardless of subject distance. The rangefinder patch is just too small and hard to see. Almost none of the 150's max-aperture shots were in focus, whether near or far. The 50, though, has such good DOF that it's hard NOT to get it into focus, regardless of aperture or subject distance. And the 80 is intermediate; wide open, it can be focused with some care; it is spectacular sharp at smaller apertures, as are all of the lenses.

I've also realized that my eyes are not doing their job lately; I need a diopter lens for this camera. I had an exhaustive vision evaluation a year ago, and discovered that I have some mild residual nearsightedness (critical only for focusing a camera lens, evidently!) ten years after LASIK surgery; a minor corneal irregularity in my right eye from the LASIK (they used a blade back then, not as accurate as today's laser-LASIK); as well as presbyopia requiring reading glasses. So it'll be interesting to see which diopter does the trick. KEH came through; I ordered all of them between -3 and +3 and I'll return all the ones that don't work. I had not realized just how hard focusing has been for me lately.

Thanks again for everyone's help.

 

[archphoto]

What you posiblycan do: ask an optician to fit a correcting lens into the holder, one that is to your prescription.
I did that with my Pentax 6x7 and it worked great.

Peter

 

[MikeSeb]

What you posiblycan do: ask an optician to fit a correcting lens into the holder, one that is to your prescription.
I did that with my Pentax 6x7 and it worked great.

Peter

that's a very good idea! If I can't get in the ballpark with the standard diopters, I'll use its frame to hold a custom lens.