After a number of false starts (instructions are scant on the subject of using Hasselblad backs on third party cameras) and trial and error I got the combination working reliably. The key issue in my mind was how do deal with the color casts across the frame that you expect when shooting non-retro focus wides digitally. This image illustrates the problem (f8 shifted 10 mm in the direction of the left side of the frame):
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Nasty isn't it.
On another thread where I first raised this issue I learned that FlexColor includes the ability to shoot a white reference frame - FlexColor applies corrections to subsequent frames based on the reference frame. Phocus 1.0 does not include this feature - this is an absolute must for the next release. In FlexColor shooting tethered you shoot the reference frame (I use an Expodisk), identify it as a reference frame; FlexColor uploads it to the back and subsequent frames are properly corrected. This too took some trial and error - the reference frame seems to work best if exposed to the middle grays. The most common mistake I made was not turning this adjustment off when shooting a new reference frame - otherwise the adjustment is corrected with the last adjustment leading to very weird results. You can use this feature shooting untethered, making the corrections when you import the images to FlexColor, but you need to tether the camera to activate the feature (think of the camera as a gigantic dongle).
So here is the white reference frame for the above image:
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And here's the image as corrected by FlexColor:
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Even on the web you see one of the advantages of the Hasselblad - absolutely lovely color straight out of the box.
Note to Hasselblad: Please, please include this feature in the next release of Phocus.