Shimming a Phase P45+ with an ALPA 12 Max

[carbonmetrictree]

I decided to calibrate my adapter plate last night after reviewing several images that were soft at f/16 and focused at infinity with an exterior of a building 50ft from the camera.

I was pretty surprised to find that my adapter required a 0.67mm shim to obtain critically sharp focus (0.15mm increase). Considering that ALPA is a company that is known for high tolerance equipment, would my adapter be fauty? If there is a visual difference with a 0.01mm shim adjustment, I would assume that this would not be a normal occurrence. (One of the reasons why ALPA has not produced a sliding back adapter was because of tolerance issues). I am also wondering if our digital backs all have a slight variation in depth, which could also be the issue for such a large adjustment. I was freaking out for a little bit, but after two hours of shimming, the camera is now happy again!

 

[PeterA]

Alpa includes a pack of shims with the Leaf Aptus, Mamiya/Phase and Hasselblad adaptors - I dont know about other backs as I only use these. I have not had to use a shim with my Leaf or Hasselblad backs. So far i have not got around to trying the Phamiya back on my Alpa.

I do know that optimal aperture with the Schneider 35 digitar is between F8-11. @ F11 I get hyperfocal acceptable focus between .5M and infinity.

I would not be surprised to find that absolute critical sharpness changes from back to back - the differences being in the back you use rather than the Alpa. I bought teh P45+ to use as a dedicated back for the Alpa in order to ensure critical focus after calibration.

Your experience encourages me to get around to testing my own set-up.

Thanks for posting.

 

[jeffreytotaro]

Hi Andrew:

Which lens were you noticing was out of focus? You need to be careful doing this sort of thing without consulting Alpa first. Infinity is often farther away than you might think. Roughly infinity is the focal length of the lens but expressed in meters, times 10. So infinity for a 35mm lens is roughly 350m, not 50'. In the case of the 35mm it is probably closer than that. Also these lenses are designed to used between f8 and f11, f16 will start to get soft from diffraction. If you want to calibrate anything it should be close to wide open. You might want to try shooting that lens at f8 with some really far off objects preferably on a cool cloudy day. Heat rising off of rooftops or parking lots can effect your perception of focus.

From Alpa:
http://www.alpa.ch/knowledgebase/qu...tune+the+adjustable+adpaters+for+digital+use?

 

[carstenw]

I don't know if this is significantly different for MF lenses, since I haven't tested, but with my Leica M lenses, I was able to tell the difference in sharpness of a 35mm lens focused at several kilometres, and on the horizon (I work in a tall building in Berlin, and can see a church several kilometres away, and a radio tower on the horizon), so I would try to get a high vantage point and focus on something *really* far away, not just 350m or whatever.

 

[carbonmetrictree]

Thank you all for your input. I forgot to mention that I also double checked my Rodenstock 28mm HR Digiron at distances between 1-15ft at f/4.5 and I seem to have had it right on the money. I'm still wondering why I didn't test out the longer distances at f/4.5 as well. I am using a Mamiya adapter (I sold the Phamiya) and believe that all of the adapters would come with a shim kit.

Jeffrey- I didn't see that on their website until now! I'll re-test my findings at f/4.5, I'm kind of surprised that I screwed up and used f/16 - it was a long day. Did you have to shim your adapter at all?


Thanks again,

Andrew

 

[jeffreytotaro]

Hi Andrew:

I didn't have to add any shims to my adapter. Check with Alpa about any issues you are having. They are very responsive and will take the time help out.

 

[carbonmetrictree]

Thank you Jeffrey, I'll email them to see what's up.