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Author Topic: Guidance on buying a digital back for 500CM  (Read 24191 times)
Anders_HK
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« Reply #40 on: July 05, 2010, 08:16:32 AM »
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@ John R Smith  and  @vandevanterSH

Quote from: John R Smith
The problems I have had with my old 500 kit are nothing to do with manufacturing tolerance, I am sure. I can shoot off a tripod with my ancient 120mm S-Planar on the most critical of still-life subjects and get razor-sharp results. It is out in the field where you can't spend half an hour setting up each shot that the snags arise.

Coincidentally my 645AFDIII is at Mamiya in Japan for adjustment of focus. Primarily the manual focus is out of adjustment. However that was not much noticeable at  very close range. Putting your issues together with this and the tolerances required for digital, could it simply be that you have is a similar issue, and that perhaps would benefit of a very detailed adjustment of the cameras? My agent tested AF as near perfect and offered adjust manual focus based on that. I still wanted Mamiya in Japan to test also autofocus to rule out any errors. My last addition is the Hassy 110/2 with very shallow DOF, thus need focus be perfect adjusted.

Also, I came across this by Alain Briot, http://www.mattsuess.com/2008/12/17/phase-...eport-part-one/

He there states that he uses 503CW and SWC, and writes of focusing:

"Focusing must be done very carefully with the P45. This is true with any lens, and more so with V-Hasselblad lenses.  V-Lenses were designed to be used with film.  Since the P45 sensor is sharper than film (the P45 has a higher resolving power than medium format film), the focus tolerances are smaller as well.

It is therefore a good idea to test your lenses to see if they focus properly.  Doing so is easy. Here’s how I did it: focus on a stationary object, with the camera on a tripod and with the aperture wide open (set at the widest f-stop for each specific lens).  Focus very carefully using magnification if your camera offers it.  After taking photographs with each lens, open the captures in your raw converter and check for perfect focus on the area where you focused.  This will tell you right away if your lenses are focusing on the proper plane or not.  By comparing photographs you will also learn how sharp your lenses are.   I did this test and found that my lenses were focusing properly with the P45, except for the 250mm lens which is not very sharp with the P45 and is also hard to focus precisely."

Further do you use screens with microprisms to assist in nailing focus ?

I hope above is helpful to narrow down.

Regards
Anders
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Anders_HK
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« Reply #41 on: July 05, 2010, 08:26:17 AM »
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Quote from: BernardLanguillier
For what it is worth, the need for a very accurate positioning of sensor vs lens mount was cited by Pentax as a major reason why they decided to go the integrated route with the 645D.

The fact that Leica took the same design decision with the S2 makes me think that it does indeed make sense.

I had interesting conversation with Nikon engineers a few years back who were focusing on improving all the aspects of the imaging chain at the same time:
- sensor
- physical positioning
- accuracy of AF
- ...

The weakest part basically defines image quality.

Cheers,
Bernard

@ Bernard,

Yup, weakest part can define image quality. However, if fabrication tolerances are strict enough, what is added is the combination of deviation from each parts exact dimension. In no way does that rule out that the concept of using a digital back works. It is only one part in chain and requires exact positioning. The more difficulty is on Cambo, Alpa, Sinar and Horseman technical type camera where things can slide and shift, thus require strict tolerance in order to move within a specific plane and thus not to deviate tolerance within such plane.

Both Pentax and Leica appear locked into smaller than FF 645 sensors, while Nikon is locked into 35mm such. The smaller the sensor, one can assume the stricter the tolerance is required. Now... if we compare that to P&S, the AA make images on all more or less not sharp... thus perhaps to hide the problem...

This has admittedly slipped far from O.P.

Regards
Anders
« Last Edit: July 05, 2010, 08:27:18 AM by Anders_HK » Logged
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