|The widest rectilinear
lens for 6 × 6 SLR Medium Format cameras of which I am
aware has a focal length of 40mm. “Rectilinear”
means that straight lines in the original subject are
still straight on film.
What about the 30mm Distagon, Zodiak and Arsat lenses?
With these lenses, most straight lines in the original subject are not reproduced on the film as straight lines. For this reason, the 30mm Carl Zeiss Distagon for the Hasselblad is excluded, as it is a “Fish-Eye” lens that renderes straight lines that do not go through the centre of the image as curved or bowed. So are the equivalent lenses in Pentacon Six mount, the excellent 30mm Arsenal Zodiak and the equivalent MC ARSAT. More information on these lenses can be seen, starting here. For examples of the distortion, see here. For certain subjects, these lenses are superb, and one does occasionally see images produced with a fish-eye lens in printed news media. It can be ideal for interior shots where there is no other way of including a large amount of the subject. But fish-eye lenses are not designed for everyday general photography and not for exterior architectural shots.
What about the 38mm Biogon?
There is another alternative: the superb 38mm Carl Zeiss Biogon, which is just a little wider than the 40mm lens. But this lens does not have a retrofocus design. In retrofocus lenses, the space between the back of the lens and the film (or sensor) plane is greater than the focal length, which allows space for the mirror that is required in SLR cameras. “SLR” means “Single Lens Reflex”, and the rationale behind that name is explained here. However, the choice of this name is not obvious for cameras that can take many different lenses, and in fact the German name is more revealing: “Spiegelreflex”, which means “Mirror reflex”.
Zenza Bronica 40mm Zenzanon-S lens
A major challenger in the Medium Format
SLR market was the Zenza Bronica company of Japan, who
produced a series of high-quality cameras in 6 × 7, 6 ×
6 and 6 × 4.5 format over a period of more than 40
years, starting in 1959. Lenses for their cameras
were originally supplied by the Japan Optical Industries
Co. Ltd. (Nikon Corporation), with other lenses from
Carl Zeiss Jena, Schneider-Kreuznach and Norita,
according to the Wikipedia
article (consulted on 1.1.19), and in later years
Bronica manufactured lenses itself.
Bronica’s 6 × 6 cameras in later years (apparently 1980-2003) were known as the “SQ” series. A 40mm lens was in the line-up. As far as I understand it (and I am not a Bronica expert), these cameras did not have a focal plane shutter. Instead, each lens had its own, built-in leaf shutter (known as Zentralverschluss in German). These shutters were made by Seiko. Now, having a lens with a leaf shutter is not a problem for a camera with its own focal plane shutter, provided there is some easy way of keeping the leaf shutter open.
An extremely skilled camera technician in Holland, Jaap de Zee, took a 40mm Zenzanon-S lens and modified it for use on the Pentacon Six. He totally removed the Seiko shutter and – much more importantly! – built a mount that maintained fully-automatic aperture control by the lever in the Pentacon Six throat! He also maintained the operation of the aperture stop-down lever on the lens, essential for checking depth of field and for stop-down metering (my preferred method).
I do not generally report on one-off modifications of lenses, but one of the big advantages of cameras with focal plane shutters is the ease with which older and larger-format lenses can be used with the camera. To modify a recent, medium format lens is definitely not easy, because of the limited space available. This skilled technician has, however, succeeded superbly.
We note that both of these lenses have a maximum aperture of f/4 and a minimum aperture of f/22.
Converting a great
lens from one great camera to another
A great lens starts with
detailed optical calculations of the shape of each
glass element and its position in relation to all of
the other elements. These elements then need to
be manufactured extremely accurately and mounted in a
barrel that will hold them securely in exactly the
right positions. But that is not all. For
high quality cameras, a modern lens must incorporate a
focussing mechanism, along with an external focussing
ring, a scale and distances that can be controlled and
read by the user. And it needs an aperture or
diaphragm: an opening the diameter of which can be
varied to control the amount of light entering the
camera and the depth of the in-focus area – again with
an external ring (the aperture ring) that can be
controlled and read by the user. Then a camera
mount is needed.
Jaap tells me that the biggest challenge of the conversion from Bronica mount to Pentacon Six mount was to get the diaphragm working automatically.
And here is the finished conversion!
What about the image quality?
Well done, Jaap!
How should one store and transport such exceptional lenses? Here is one possible solution:
There is no need for any anxiety about
this; the lenses for Bronica cameras have a high
reputation, earned from their reliable performance in
the hands of professionals over many decades. And
the Dutch technician who modified this lens for use with
cameras that have the Pentacon Six mount did an
excellent job. Infinity focus is spot-on. I
always use the focussing screen for focussing, so I have
not checked the accuracy of the other distance markings
on the lens. However, these have not been changed,
and if infinity is right, they will be right, too.
In September 2018 I posted one picture
from this lens on the page that introduces shift lenses
(here) – in order to
compare angles of view and the effect of using a shift
lens. (This lens is not in a shift mount.)
Here we shall look at some more pictures, all of them
taken with my usual Pentacon Six camera.
First, two images taken with seconds of
It is clear that the angle of view is virtually identical with these two lenses. From the markings in the gravel, it looks as though I tilted the tripod head up slightly before the Zenzanon picture, and also there is a tiny bit less of the path on the left and a tiny bit more of right-hand building visible, no doubt also from a slight horizontal movement of the tripod head when changing over the lenses.
There is a tiny amount of vignetting (darkening of the corners) with the Curtagon lens – although you more or less have to be looking for it in order to see it. It could easily be corrected in software, but on this website we like to show things as they really are, before any corrections or improvements. So the Zenzanon looks fractionally better than the Curtagon in this regard.
Let us see two more images shot on the same day at Leeds Castle in Kent.
At a massive degree of enlargement on my large computer monitor, I can see a tiny amount of colour fringeing (chromatic aberrations) in the corners with images from both lenses. However, this is at a level that is not observable at normal degrees of enlargement or from normal viewing distances. It is well within the range that is correctable with minimal tweaks in software, but that is not something that we are here doing. The Zenzanon is sharper in the top right corner than the Curtagon.
As is typical for an English summer’s day, even one as lovely as this one, there are some clouds in the sky – even though none of them appear in these two images! – and as they move, so do the shadows that they cast. Thus in the Curtagon panoramic shot, the sun is on the bridge but the leaves in the foreground are in shadow, while in the Zenzanon photo the sun is on the leaves in the foreground and on the church in the distance, but not on the bridge. Nethertheless, we do obtain a reasonable impression of these two lenses, and either of the images is equally acceptable.
For a further test image shot with the 40mm Zenzanon lens, see here.
More images shot with the 40mm Curtagon can be seen here.
To go back to the beginning of the lens tests, click below and
then choose the focal length that you want to read about.
Back to beginning of lens tests
© TRA January 2019 Revised: June 2021