The 40 mm CF Distagon is a good lens, but as any wide angle a bit less in the corners and near the edges.
Still good though.
But whether it will cover 6x7 ... ?
The 50 mm Distagons are not too bad either. Not as good as longer focal length lenses, but still o.k.
But if a 50 mm, let it be the FLE version, either with or without shutter. And the CF/CFi FLE is better than the F/FE lens. Lighter too (i find that an issue with the f/2.8). So the CF/CFi would be the better choice.
Again, i don't know whether they will cover 6x7.
I do agree with other answers though: why not use the Pentax lens?
Just to muddy the water a bit more: I have it on good authority that the very large 40 for the Hasselblad is a bit turkeyish; lots of flare and stuff, and not terribly sharp., The newer one, much smaller seems good. I saw one sold for somewhere close to $4000 an Ebay. I am old and stupid but not crazy.
I have a 40mm Distagon for the Rollei SLX/600x series, which is reputed to be the same optics. It's PLENTY sharp, although it is quite sensitive to flare.
Originally Posted by RJS
I spent around ~$900-950 for mine via ebay.