Pentacon Six System
What image do
I get when I use a Pentacon Six lens
on my 35mm camera
or on my digital camera?
It can be difficult to understand in
advance what the effect is going to be when a Pentacon
Six lens is used on a 35mm camera, or even on a digital
camera with a sensor that is smaller than the "full
frame" 35mm size. Here is a typical question,
received in March 2016 from a visitor to this website:
Q: “ Hello
Thanks for providing this great resource with your
website! I have recently bought two Zeiss lenses with a
Pentacon Six mount: a Flektogon 50mm/f4 and a Biometar
80mm/f2.8 (both as "zebra" versions) and mounted them
via a "lensless", plain "mechanical" adapter to my Nikon
D810. What a joy to use them!
What I did not understand from the information on your
website: what exactly is the equivalent focal length
when mounted on a full frame camera? I had the
impression from your list on
that they would have a different angle of view, when
mounted on a 35mm camera. Optically, I do not get
a wider or narrower angle of view - the Flektogon 50mm
for example shows the exakt same field of view as my
normal 50mm Nikon lens. Where is my error of thinking?
Furthermore, I’d like to ask: the lens's calculation is
done to properly fill the medium format. Mounting it on
a full frame camera - will it produce better results
(better corner sharpness, less vignetting), because only
the central part of the lenses "projection" is used by
Thanks for your help
Here is the
reply that I sent him. I have added titles
for the purpose of this web page.
A: Hello J
Thank you for your e-mail.
Angle of view
and how much of the scene is covered
The purpose of my page of 35mm and medium format
equivalent focal lengths is to help people who are
familiar with what they see through a given lens on a
35mm camera to find out what lens they will need in
order to see (approximately) the same amount of the
scene before them on a medium format camera such as the
As you have discovered, a lens with a
focal length of 50mm still has the same focal length,
regardless what camera it is mounted on: its optical
characteristics obviously don't change.
The only thing that changes is the amount of the scene
before it that is included on the film (or sensor). So
to see on a 35mm camera the same the amount of the scene
that Flektogon records on the 6×6 frame,
you would need a lens with a focal length of a little
under 28mm on the 35mm camera. However, if you
mount the 50mm Pentacon Six Flektogon on the 35mm
camera, it is still a 50mm lens, so it will show the
same amount of the scene as a 50mm lens that had been
designed for the 35mm camera in the first place. In
fact, it has the inconvenience of being larger and
heavier than a 50mm lens that had been designed to cover
only the 24×36mm 35mm "full frame" format.
the focal length doesn't change, only the amount
of the scene that is in front of it that is
reproduced on the film, which is determined by
the size of the film:
smaller film area = smaller amount of original
So when the 50mm Flektogon is used on a
35mm-format camera, the image on the film (or
sensor) will the same same size and coverage as
an image shot with a 50mm lens that had been
designed for the 35mm camera.
The question is a different one:
If I know what the 50mm Flektogon shows me on my
what lens do I need on my 35mm camera, in order
to see the same amount of the scene?
Answer: a lens slightly wider than
28mm focal length
(as indicated on the chart referred to in the
we could ask a question in the opposite
I have a 28mm lens on my 35mm (full-frame)
What lens would give the same amount of the
scene on my Pentacon Six?
Answer: a 50mm lens such as the
Now to your other question, which concerns the
resolution of the image. With all lenses,
resolution reduces as one moves further away from the
centre of the image. In fact, all lenses project
an image that is, in absolute terms, larger than the
required format. However, resolution and brightness both
reduce as one gets further away from the centre of the
image, so they are designed to give adequate resolution
and (supposedly) no obvious reduction of brightness
(called "vignetting") within the intended
So the Flektogon should give a sharper and more
evenly-illuminated image on a 35mm camera than a 50mm
lens designed for a 35mm camera. Of course, this
all depends on the quality of the lens designed for the
You should of course get NO VIGNETTING AT ALL when using
the 50mm Flektogon on a 35mm camera, so it will be
better than many 50mm lenses that are designed for 35mm
cameras (where there often is visible vignetting).
As regards resolution, as images shot with a medium
format camera need to be enlarged a lot less than images
shot with a 35mm camera, some very expensive lenses
designed for a 35mm camera may well in theory have a
higher resolution than the 50mm Flektogon, although I
don't have any figures for this. However, because
of the greater degree of enlargement of the image
recorded on the film that is required with a 35mm
camera, the resolution of the resultant image
even if shot with a super-high-resolution lens on that
35mm camera will not be higher than the resolution of an
equivalent image that was shot with the Flektogon on a
More important, since the size of the
film surface is much smaller in the 35mm camera, factors
such as film grain are likely to make the image from the
35mm camera have MUCH LOWER RESOLUTION than the
resultant image from the Pentacon Six, because the chief
limiting factor with equipment of this quality is not
the lens but the resolution and grain structure of the
film itself. The gradation, for instance of skin
tones, is frequently also far smoother on a 6×6 image
than on a 35mm image.
Finally, when mounting the Flektogon or
any other medium format lens on a 35mm camera (or
smaller, such as a digital camera with an APS-C-sized
sensor), it is essential to ensure that the adapter is
absolutely matt-black inside, with no reflective
surfaces. The reason for this is that the medium format
lens covers a wider area of the original scene and
transmits a much larger overall image than a lens that
was designed for use on the 35mm camera. None of
the light from that "wasted" image must be allowed to
"bounce around" or reflect within the adapter, since if
it reaches the film, it will reduce the contrast and
quality of the result.
This problem is almost unheard-of, but, many years ago,
I did have a poorly-made adapter that was not matt black
inside, and when I tried out a 50mm Flektogon on a 35mm
Minolta SR-T 101, reflections occurring within the
adapter did reduce the contrast of the image in the
main use for medium format lenses on 35mm cameras
In my option, there are two the principal
uses for medium-format to 35mm adapters
- to enable photographers to use the
LONGER medium format lenses on their 35mm camera, and
in these circumstances the result is usually extremely
- to enable photographers to take
advantage of the larger size of the image projected by
the medium format lens, in order to use a tilt or
shift adapter to achieve other effects in their
image. (See introduction to shift and tilt
lenses, starting here.)
A problem with some digital sensors
Another problem can occur when using with
digital cameras wide-angle lenses that have been
designed for film cameras, due to the design of
sensor protector in some digital cameras, which
may have a honeycomb-like structure (like a series of
pencils bundled together and stood on end). This
requires the image-forming cone of light that enters the
image area to be almost the shape of a canned drink,
i.e., with nearly parallel sides. Wide-angle
lenses by definition have to bring in the rays of light
that form the image at a much greater angle, a real
cone-shape. The result can be some vignetting in
full-frame digital cameras when using lenses that have
been designed for full-frame film cameras, even when
those lenses do not vignette when used with film.
I hope that this is helpful.
With best wishes
"Mr Pentacon Six"
A related question that I have also just
received is this one:
Q: “ Hallo,
Thank you very much for bringing to your website so
much valuable info regarding Pentacon-Six System.
My idea is to use (with aproppriate adapter) one of
those P-Six lenses on my Nikon D300 (APS-C
Matrix). I am wondering what the 'crop factor'
would be when using P-Six lens on DX camera.
It is 1,52 for FX lenses when using them on DX. The
middle format lenses which are P-Six fit bigger matrix
format than FX.
Could you please give me a hint ?
A: Hello M
Thank you for your e-mail. As you will see from
the above explanation, a 50mm Pentacon Six lens is still
a 50mm lens when it is mounted on a 35mm full-frame
camera, and of course it is still a 50mm lens when it is
mounted on a camera with an APS-C-sized sensor or
The idea that manufacturers had when introducing
the concept of "crop factor" was to tell
potential customers who were familiar with full
frame 35mm cameras what the image would be like
if lenses from those cameras were used on their
new camera that had a much smaller frame size or
Since the smaller frame or sensor is cutting
off, or cropping, the edges of the
image, you will only see a smaller portion of
the scene being photographed.
If you have a mental image of the coverage of a
lens with a focal length of 50mm on a 35mm
camera, if you put that lens on your APS-C
camera, it will only record the central area of
How much will it record?
The "crop factor" tells you. In
this example if we multiply the 50mm by 1.52, we
get the number 76.
So the image that your APS-C film or sensor will
record will be the same as what you would have
got on a full-frame 35mm camera if you had used
a 76mm lens.
Manufacturers have (with few and very minor
exceptions) never tried to explain a
"medium-format to APS-C crop factor", because
there was not amongst most consumers a public
that was familiar with the coverage of different
focal lengths on medium format cameras.
So a 50mm lens is a 50mm lens.
On a medium format camera it will show a certain
amount of the scene before it.
On a 35mm "full-frame" camera it will show a lot
less (we might say a little more than half the
width, and a little less than
half the height).
On an APS-C camera it will show less still.
I hope that this will make the whole
matter a little easier to understand.
"Mr Pentacon Six"
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© TRA First published: March 2016