microprism screen for mamiya 645 afd

[Mort54]

jack....i understand your concerns....i have no way of explaining this or even really understanding...the info is straight from bill maxwell, who custom makes some of the best screens for any camera....

I also spoke to Bill Maxwell a few weeks ago, and he told me the same exact thing. That if you change the screen, you may throw of the AF a bit and you may need to send the body back in for AF recalibration. He indicated the reason was that Mamiya screens had a lot of variation in them (curvature variation). You might get lucky and not need to recalibrate. But then again, you might not be lucky.

To answer another poster, the screens themselves are interchangeable. But that doesn't mean the AF doesn't have to be recalibrated when you change the screen.

I personally don't know what the truth is, but Bill Maxwell is one of the most highly respected suppliers of custom screens, and he certainly knows his stuff.

[pss]

I also spoke to Bill Maxwell a few weeks ago, and he told me the same exact thing. That if you change the screen, you may throw of the AF a bit and you may need to send the body back in for AF recalibration. He indicated the reason was that Mamiya screens had a lot of variation in them (curvature variation). You might get lucky and not need to recalibrate. But then again, you might not be lucky.

To answer another poster, the screens themselves are interchangeable. But that doesn't mean the AF doesn't have to be recalibrated when you change the screen.

I personally don't know what the truth is, but Bill Maxwell is one of the most highly respected suppliers of custom screens, and he certainly knows his stuff.
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personally i trust bill more then what someone at mac or mamiya will say...they won't admit that there are variations in the manufacturing.....i understand that....the question is how often and how much (to which extent) does this actually manifest itself....bill is a stickler for quality and i am sure he can back all this up with data.....
bottom line: one MIGHT have to send the body in for calibration....not the worst thing in the world....i guess it should go in every year or so anyway.....

[Jack Varney]

Bill Maxwell may be correct regarding unintended or random differences in the screens. Heat and handling can certainly have its affect on plastic which is what the screens are made from.

However, the original question was whether the screens are made for or tailored to a specfic body. They are not.

That said, after changing my AFD to a Type C screen I did a focus test, i.e. back/front focus and edges/center. I found the replacement screen to be within a mm or so on back/front focus. I wonder if the original screen was as good, as I did not test it!

[Don Libby]

I switched my focus screen shortly after I got the Hartblei and 300 f2.8 and have had no problems with focusing.  Actually I’m glad I changed screens as it just appears to be easier whether I’m using AF or MF lens; I find that I’m switching my AF to MF more and more  

I had thought about having a custom screen made but since finding the proper way to place the Phase One P30 focus overlay I’ve decided to place that on hold for now.

[awofinden]

I switched my focus screen shortly after I got the Hartblei and 300 f2.8 and have had no problems with focusing.  Actually I’m glad I changed screens as it just appears to be easier whether I’m using AF or MF lens; I find that I’m switching my AF to MF more and more 

I had thought about having a custom screen made but since finding the proper way to place the Phase One P30 focus overlay I’ve decided to place that on hold for now.
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What is the proper way?

[Jack Varney]

Place the overlay screen under  the focusing screen, i.e. on the mirror side. Maybe it should be called an underlay screen.

[eronald]

Place the overlay screen under  the focusing screen, i.e. on the mirror side. Maybe it should be called an underlay screen.
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Are you sure ? I would have thought this would the focusing screen up by one thickness, guaranteeing bad focus.

Edmund

[Don Libby]

During my first two attempts to get the little plastic in I too thought it needed to lay on top of the screen.  I never could get everything to line up correctly and then decided what the heck just don’t use it.  I posted a question here several weeks ago about getting a custom screen made and it was during that thread that I learned I had been attempting to mount the plastic screen all wrong, so disregarding the instruction I placed the bracket screen first on the metal holder then placed the focusing screen on top of that and closed it.  No problems whatsoever this also includes close to 6 hours on a 19’ boat in very choppy waters last week in Lake Powell.  If I had to find one gripe about Phase it would be the plastic bracket screen.  I had a Kodak Pro Back that had a crop factor but Kodak had an actual focus screen replacement instead on stacking like I currently have to do.  But as I said earlier no problems so far …..


don

[Jack Varney]

Don is right. If you think about it the metal frame that holds the screen closes and locks, with the screen in place, to a fixed position above the screen holder. The plane of this position, at which the screen stops, is the plane of focus of the viewfinder system. The body is engineered so that this position is at the same focal distance as is the film or sensor plane.  So, now when you change a screen and lock the frame into position it will consistently lock the screen against this reference point, i.e. assuming that the frame locks firmly, as it has for me.

Now, if you place the overlay above the focusing screen it will force the screen to a position below the focus point by the amount of the thickness of the overlay screen, i.e. about 1/000 inch. Thus, focus will be changed by 0.0007873 nanochrons. Or , somehthing nearby.  

If you feel as I do that this should be termed an underlay screen my only suggestion would be to write your congressman to request that the name be changed.

Thank you for your intrest in this subject!