Pentacon Six System
How the Exakta
66 metering prism
Note how the front of the metering prism
of the front of the camera
and comes down to sit snugly against the
To see how to
operate this metering prism,
I am regularly asked questions about the
Exakta 66 metering
prism. Here are the answers.
Q1 Can I
use the Exakta
66 metering prism on the Pentacon Six?
No. It is not possible to mount the
Exakta 66 metering
prism onto a Pentacon Six body. This is because
the front of the
prism extends forward and down, and the strap lugs on
the Pentacon Six
body prevent it from being mounted.
It may possible to mount an Exakta 66
on a Pentacon Six, but it blocks the end of the camera
shutter-advance lever and so should not be used.
In my opinion it also looks a little odd and it brings
no gains, as inside the black plastic housing is an
Pentacon Six plain prism.
does the Exakta 66
metering prism work, then?
The Exakta 66 metering prism requires the
input of the
same three pieces of information as any other meter,
plus a fourth piece
of information in most cases.
1) First, it needs to know the
of the film. This is input by the user by
adjusting the ISO dial
on the top of the meter when loading the film into the
is thereafter not touched, unless a film with a
different sensitivity rating
2) Secondly, the prism needs to know
speed selected on the body. Here (and in points 3
and 4) the Exakta
66 is a great advance on the metering prisms for the
Pentacon Six and the
Kiev 60, as the shutter speed selected on the body is
transmitted via electric
contacts to the metering prism.
Note the seven gold-plated pins on the
underside of the
metering prism, on the left,
and the seven gold-plated contact points
on the camera
body, on the right.
These transmit the selected shutter
speed to the metering
circuit in the prism.
The metering prism will not give a
reading until it receives
shutter speed information from the camera body.
This is another reason
why it cannot work on a Pentacon Six, which does not
have the contacts
that provide this information.
3) Thirdly, the metering prism needs to
know the aperture
value selected on the lens. This, too, is
automatically input into
the metering prism, although not electrically. The
input system is
A in this image is pointing to
the raised cam
that is on a spring-loaded mount on the back of the
aperture ring of all
Schneider-Kreuznach lenses for the Exakta 66.
Arrow B is pointing to the
middle of the nine
contact points on the underside of the metering prism.
(In fact, there are more than nine, as
is explained below.)
As the lens aperture ring is rotated, the
cam (A, above)
presses in turn on one or two of the contact points on
the metering prism,
inputting the value of the aperture selected.
|Suppose we number the contact
points 1 to 9, as I
have done in the image to the right.
Depressing contact point 1
inputs the f/ stop value
f/2 to the meter. (I am not aware of any
f/2 lens for the Exakta
66, but if you get or make one, you will be
able to input the aperture
Depressing contact points 1 and
the value f/2.4 - the vertical line on the LCD
readout between f/2 and
f/2.8. (The same comment applies!)
Here are all of the
||Aperture value input
|1 & 2
|2 & 3
|3 & 4
|4 & 5
|5 & 6
|6 & 7
|7 & 8
|8 & 9
4) The fourth piece of information that
the metering prism
requires is the maximum aperture of the lens. This
is input via a
pin on the lens that depresses one of a series of
switches on the prism.
The default aperture is f/2.8. When none of these
switches is depressed,
the meter assumes that the maximum aperture of the lens
is f/2.8, which
is the case with the 80mm lenses (only), which is why
these lenses do not
need this extra pin.
|On this 60mm Curtagon lens, the
maximum aperture pin
is indicated with the arrow marked with the
letter P. It is behind
the cam that inputs the aperture that has been
selected - beneath it, when
the lens is mounted onto the camera.
If you now look back to the
previous picture, you will
see that the contact points that, by my
numbering system, are 1, 2, 8 and
9 are double the height of the
others. For each of these four
contact points there are two switches,
one above the other.
The top one is actuated by the rotating
aperture cam on the lens aperture
ring. The bottom one is actuated by the
maximum aperture pin that
is to be found on all lenses other than those
with a maximum aperture of
f/2.8, which is the default aperture, for
which no maximum aperture switch
The other maximum apertures in
the Schneider Exakta 66
lens range are:
||55mm Super-Angulon PCS
Perspective Control lens
|The Schneider 2Χ converter is
designed to work
with lenses of 150mm and longer, and with the
75-150mm Variogon zoom lens.
(The early publicity and the instruction manual,
which state that it can
be used with the 80mm lens, is wrong.) It
therefore has a rotating
ring that enables the user to input a maximum
aperture of f/4, f/4.5 or
It achieves this by using two
pins on different
parts of the ring. For most apertures,
only one pin is used, with
the unused pin being in a non-contact
position. For f/5.6, both
pins are used. The two pins are arrowed
in the image to the right.
On this converter, the top ring
as seen in this image operates
the maximum aperture pins, which are at the bottom.
chosen aperture ring, which is between them
(and is set at f/11 in
this photo) moves the cam to tell the meter
which aperture has been set
on the lens. (It doesnt actually
change anything on the lens;
the same aperture number must be
set on the lens and the converter!)
The maximum aperture switches
on the metering prism are
(bottom row of
The Exakta 66 bellows switch
the meter to stop-down metering.
To do this they depress two
switches on the prism, using
two pins. The two switches are Switch
position 1 (by my numbering
system): top and bottom
The original Exakta 66
extension tubes (not the Pentacon
Six equivalent tubes) have a little lever that
also depresses the same
two switches: Switch position 1 top and
lenses from other manufacturers with the Exakta
66 metering prism
Q3 I have an
Exakta 66 body.
Can I use the Exakta 66 metering prism on it with non
The short answer is no, unless you modify
And most non Schneider lenses cannot be suitably
The Exakta 66 metering prism only gives
a Schneider lens is mounted on the body. This
depresses an electrical
contact on the underside of the front of the prism to
tell it which aperture
has been chosen. A second pin on lenses with a
maximum aperture other
than f/2.8 inputs the aperture value to the metering
circuit in the prism.
Q4 Could I
not add the necessary
pins to a lens to activate the contacts in the prism?
It might be possible to modify lenses by
adding a pin
that would depress the maximum aperture contact and a
cam on the aperture
ring that would depress the correct selected aperture
contact, but there
are two problems with this:
Most lenses have the aperture ring too far
make the design of such a cam easy.
Many lenses rotate the aperture ring in
direction to the Schneider lenses.
which lenses might
The Schneider-Kreuznach lenses for the
Exakta 66 have
the largest aperture size (the smallest number)
at the far left
of the aperture ring, viewed from above. Carl
Zeiss Jena lenses have
the largest aperture at the far right of the aperture
ring, viewed from
above, so rotation is in the opposite direction.
The 80mm Schneider-Kreuznach Xenotar MF
for the Exakta
66, on the left,
and a late example of the 80mm Carl
Zeiss Jena Biometar
for the Pentacon Six, on the right
Note the opposite direction of rotation
of the aperture
ring (the bottom ring in this view).
As the aperture ring on the Schneider
lens is rotated,
a cam on it depresses contacts on the Exakta 66 metering
prism to input
the aperture value selected. Even if the aperture
ring on a Carl
Zeiss Jena lens were fitted with a suitable cam, it
would input the wrong
values (at all apertures except potentially one).
As regards the Arsenal lenses from the
FSU, there is no
standardisation as to the direction of travel of the
aperture ring: some
rotate the aperture in one direction, and some in the
other, so some might
in theory be adaptable and others not. The 65mm
Mir 38B, the 80mm
Arsat and Volna standard lenses, the 120mm Vega, the
250mm f/5.6 Arsat
or Telear and the rare 45mm Mir-69 have the same
direction of travel as
the Carl Zeiss Jena lenses, so could not be adapted.
Others, such as the 45mm Mir-26, the
150mm Kaleinar and
the 250mm f/3.5 Jupiter, have the aperture ring rotating
in the same direction
as the Schneider Exakta 66 lenses, but on these three
lenses the aperture
ring is near the front of the lens, forward of the
focussing ring, whereas
it needs to be at the back of the lens if it is to
connect to the metering
prism, so they cannot be adapted either.
Q6 Could I
modify a lens
from another manufacturer?
Well it would need to fulfil the following
1) Have a Pentacon Six lens mount
2) Have an automatic aperture pin
is no point in even trying to adapt for use with the
Exakta 66 metering
prism, whose default setting is for open (or full)
3) Have an aperture ring that
rotates in the correct
direction (with largest apertures on the left, viewed
4) Have the aperture ring at the
back of the lens
5) Have an aperture ring of the same
as the aperture rings on all the Schneider E66 lenses
6) Have the same physical spacing on
ring between the different aperture settings.
Bear in mind that the physical distance
travelled by the
aperture ring on Arsenal lenses is not standardised:
some travel further
than others to change the aperture by one stop,
depending on the diameter
of the lens. Therefore wrong values would be input
at most settings,
even if everything else was right.
If you managed to achieve all the above,
then you would
be ready to try to meet the final two requirements:
7) Install a pin that would input
the maximum aperture
of the lens to the metering prism (unless it were f/2.8,
in which case,
no pin would be required). Tom Page did this for
me with the 40mm
Curtagon, details of which you can see, starting here.
8) Install a cam that will input the
aperture value into the meter.
In practice, I only achieved my
modification by inserting
the optical assembly of the 40mm Curtagon into the empty
lens chassis of
an 80mm Exakta 66 lens that I sacrificed for the
Q7 Can I
trick the meter
It is possible to trick
the meter by
using two straightened-out paper clips or other similar
objects to depress
the correct contacts, but one needs two hands to do
this, plus a hand to
hold the camera, unless it is on a tripod, and one needs
to move to the
front of the camera in order to see the contacts, so it
is not possible
to look through the viewfinder at the same time.
Even though all of this can be achieved
in a laboratory
situation, it is not practical for actual taking of
photographs in a real-life
situation, and is impossible to achieve with a hand-held
Therefore it is as good as useless. It is for this
reason that I
say that the Exakta 66 metering prism only works with
the correct Schneider
lenses designed for use with this camera.
To go to introduction to the cameras,
To go back to the introduction to the
prisms, click here.
To choose other options, click below.
© TRA First published: July 2011
Revised: May 2020