Hasselblad V and Credo/Phase One back - focus considerations?

[kofa-king]

Hello all,

This is my first post here in this wonderful group that has served me plenty of help over the years! I searched around but couldn't find lucid information regarding my questions.

I have a Hasselblad V system and am looking to mount a V-mount digital back to the camera and breathe some new life into it. As many of us know, in order to get the correct framing, a viewfinder mask must be installed *below* the focusing screen as per the manufacturer instructions (see Credo documentation here: https://manuals.directutor.com/mami...00300a-179960-user-manual/index.html?page=123)

My question is: would this affect critical focus if you are changing the distance between the mirror and the bottom of the focusing screen? Can the viewfinder mask be installed *on top* of the focusing screen successfully? What have others done in the past?

Thanks for your help!

 

[FloatingLens]

I had the same reservations, but eventually I figured this out: the cutout masks that are supposed to be installed beneath the focussing screen do not change the screen distance. This is because the Hasselblad screens protrude by a fraction of a millimetre in the four corners whereas the mask has those four edges slanted.

(disclaimer: Phase One info... I assume same principle applies for your mask)

 

[kofa-king]

Wow, this is a really good point. I hadn't even considered that! Thank you for this helpful information.

 

[Hasslebad]

I put the plastic phase one mask on top of my ground glass. It felt really tight when I stuck it underneath. I probably didn’t install it right underneath so instead of risking misalignment, I used 3M double-sided tape and installed it on top of the glass. The waist level viewfinder closes over the mask fine. The only issue is that it gets dirty and to clean the glass well, I do have to occasionally remove the plastic mask.

 

[jng]

As noted above, the Phase One masks have the corners trimmed off so they don't alter the height of the focusing screen. The thing you need to check on is whether the focusing path (a function of mirror alignment and focusing screen height) is properly calibrated relative to the sensor plane. "Creep" of mirror alignment generally occurs with use, requiring periodic checking and maintenance over time.

John

 

[Godfrey]

I use the Hasselblad CFVII 50c digital back on my Hasselblad 500CM bodies. For best focusing performance and accurate framing, I bought Hasselblad H-3042264 focusing screens for the 500CM bodies. These have a better, higher contrast surface on which to focus, a very accurate rangefinder split-prism focusing aid, and the format framing lines for the digital back scribed onto them. They're just as useful for shooting with when I switch to an A12 or A16 film back as well. (For A16 film back, just extend imaginary format diagonal lines to the screen edge for the proper framing, and use the whole screen for A12.)

I find this solution far, far better than fitting masks. It is, of course, rather a bit more costly.

G

 

[jng]

Note that the Hasselblad screen mentioned by @Godfrey would be fine for framing the Credo 50 (33x44mm sensor) but won't help you with the Credo 60 or Credo 80 (40x54mm sensor). The latter will require either a focusing mask or one of the gridded Hasselblad screens (don't recall the part number off-hand) where the outer lines are pretty close to marking the 645 format.

John

 

[Godfrey]

If you need precise format lines, I agree. But if you use the same trick I use with the above screen to visualize 645 framing, you can use the same screen. It all depends on how precisely you need to frame with an explicitly defined edge.

G