The Pentacon Six System
Is it possible to modify Pentacon
so that they can be used on
the Pentax 6×7?
There are two difficulties with modifying Pentacon Six lenses to Pentax
Firstly, the image diagonal of the Pentax 6×7 is obviously
significantly larger than the image circle of the Pentacon Six:
The diagonal of Pentacon Six (56m × 56mm) is fractionally under 79.2mm.
The diagonal of Pentax 6×7 (55mm × 70mm) is 89mm.
Any lens that one hopes to use on the larger format must have an image
circle large enough to cover the diagonal without noticeable vignetting
or fall-off in resolution. (Obviously, the image projected onto the
film gate for any Pentacon Six lens has to have a diameter significantly
greater than 79mm, as with any lens there is a fall-off in resolution and
brightness towards the edge of the image (see the section on shift
& tilt lenses). Likewise, the image circle of any lens
used on the Pentax 6×7 must be significantly larger than 89mm.
It might be good to start with lenses that have been adapted for use shifted
on the Pentacon Six, as it will be clear that they will have a significantly
larger-than-normal image circle with acceptable definition and absence
of vignetting. I have read that the 55mm Arsat shift lens generates
image circle of diameter of about 105 mm at f/4.5 (wide open) and about
110 mm at f/22.
I have read of Pentacon Six lenses adapted for use on the Pentax 6×7,
but these must have been one-offs, never commercially in serial production.
I also doubt very much that it would be possible to retain auto aperture
operation. A vendor in Kiev advertised one of the shift lenses
in a Pentax 6×7 mount, with no auto aperture and a very high starting
price on eBay (I seem to recall US$2,000). In that auction it did
However, the second difficulty is harder to crack. This is the
distance – the distance between the rear flange of the lens that mates
with the front of the camera and the film plane. The register distance
of the Pentacon Six is 74.1mm, and it is clear that if one wishes to mount
a Pentacon Six lens on a 35mm camera body that might have a register distance
of, say, 45mm, there will be space between the rear flange of the lens
and the front of the 35mm body, to insert an adapter. This is not
the case with the Pentax 6×7, for which I am told that the register
distance is 84.95mm. If this is correct, then the Pentacon Six lens
would need to be recessed over 10mm (not far short of half an inch!) within
the throat of the Pentax 6×7, if one wanted to obtain infinity focus.
If it is possible to cut significantly more than this length off
the back of the Pentacon Six lens (to allow space also for the adapter),
then using the lens on the Pentax 6×7 may be possible. But
most Pentacon Six lenses have one or more elements within the final 10mm
of their length.
So such lenses may be usable as macro lenses on the Pentax
6×7 – where the bellows extension will also increase the projected
image circle – , but could not be used for normal photography with infinity
David Cross in England e-mailed me in March 2006 that he has
converted some Pentacon Six lenses for a Pentax 6×7. Here is
some of what he says:
“So far I have adapted the Pentacon 300/4, the CZJ Sonnar 300/4
(which slips nicely into an outer bayonet extension tube with minimal machining)
and a zebra finish Sonnar 180/2.8; this particular lens had a rear element
assembly/baffle in two parts so required no machining off the length of
the baffle-I have another sample of this lens which would require machining
here. These adaptations have no stop-down linkage - not something
I feel is too much of a problem in use.
David has kindly agreed to let me give his e-mail address, so that visitors
to this website with questions about adapting Pentacon Six lenses to the
Pentax 6×7 can contact him directly. Here it is: email@example.com
(Copy and paste this into the address line of your e-mail software; this
is not a live link.)
“Feel free to pass on any enquiries on this subject to me.”
I have also recently read a report of a professional photographer working
with a Pentax 6×7 with a modified Pentacon 500mm f/5.6 lens.
This is a great manual lens (with pre-set aperture ring, which speeds up
The opposite question has also been asked: “Is it possible to use
Pentax 6×7 lenses on the Pentacon Six?” To see a consideration
of this, click here.