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Stasi Zeiss Pentacon
The camera – basically a modified Praktica EE2 35 mm SLR 2 –
has a standard M42 thread (also known as Praktica-mount) which allows a wide
range of standard lenses to be used. In addition,
adapter rings were available
for use with special surveillance lenses and
high-end pinhole lenses.
The image on the right shows the GSK with an
f3.5 135 mm lens (SO-3.4)
that was developed especially for use in observations and covert
surveillance. Lenses with a different focal length were also available.
These lenses have an M36 mount, for which an M36/M42 adapter is used.
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The above configuration would normally be operated from inside a
concealment, such as a shoulder bag or a piece of furniture.
Depending on the circumstances and the expected distance to the
target, one of several lenses would be selected from the
Stasi's Special Optics (SO) range.
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In addition to the regular lenses from the SO-series, the Stasi
also used special pinhole lenses that were developed by
Carl Zeiss
in Jena (DDR). A pinhole lens requires just a tiny little hole –
typically 1 to 3 mm – to create a high-quality image,
without the risk of being detected.
The image on the right shows a GSK fitted with an
SO-3.5.1 pinhole lens,
two range extenders (2x and 2.5x) and an M36/M42 adapter
ring. For adjustment, a 90° viewfinder is fitted over the regular eyepiece.
It has to be removed once the camera lens is adjusted to avoid light-leakage.
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Development of the camera started in the early 1970s at the request of
Department 31 of the OTS of the Stasi, and was carried out by Pentacon
under Stasi project number 14101. The aim was to develop a universal low-noise
35 mm SLR camera that was suitable for covert photography [3].
A lot of research had already been done in the mid-1960s
at the East-German Science Academy in Berlin
— Deutsche Akademie der Wissenschaften (DAW) 3 —
for the development of a static
semi-transparent foil-based mirror 4 that could
replace the noisy mirror of a regular SLR camera [D][E].
The geräuscharme Spiegelreflex Kamera (GSK)
was given the model number SR 899, and went into
production in 1977 at the Pentacon production facility
Objekt 8
in Dresden-Niedersedlitz in the DDR (East-Germany). Although the
exact production quantity is unknown, it is estimated from the surviving
serial numbers that around 2000 units were manufactured [1][3].
➤ History of the GSK (off-site)
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GSK = Geräuscharme Spiegelreflex Kamera (low-noise reflex camera).
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Based on the design of the Praktica EE2.
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In 1972 renamed Akademie der Wissenschaften der DDR.
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Pioneered by Canon in the Pellix camera in 1965. ➤ Wikipedia
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Below is a quick overview of the features on the bare body of the GSK.
The camera is based on a standard Pentacon 35 mm SLR camera with a motor
winder bolted to the bottom. The camera has been modified to produce as little
noise as possible. For this reason the mirror has been replaced by a
semi-transparent foil
that does not flip out of the light path when taking pictures. To avoid light leaking from the viewfinder to the lens, the
viewfinder can be closed with a hinged flap.
The lens port has M42 thread, also known as Praktica-mount, for which a wide
variety of lenses was available at the time. For observations, the
Stasi had selected four lenses with a focal length of
35, 50, 75 and 135 mm respectively.
For covert surveillance, such as in hotel and conference rooms, the Stasi
used the SO-3.5.1 pinhole lens, that came with a
set of three range extenders.
The image above shows the GSK camera with the
SO-3.5.1 pinhole lens and all
three range extenders (2.5x, 2x and 1.5x) bitted between the lens and the
camera body. Note the presence of the M36/M42 adapter ring between the lens
assembly and the input port of the camera.
➤ More about the SO-3.5.1 pinhole lens
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Camera
SR-899 (GSK) 899 001
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The basic SR-899 camera consists of two integrated units:
a modified 35 mm camera – based on the design of the Praktica EE2
SLR – and a low-noise motor-drive.
The camera is unique in that the noisy mirror of the SLR is
replaced by a static semi-transparent foil, that is not flipped
out of the light path when shooting pictures.
➤ Read the manual
➤ Take a look at the foil-based mirror
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This 90° periscope could be attached to the eyepiece of the
viewfinder, to aid the adjustment of the camera under difficult
conditions, for example when the camera was installed inside a piece of
furniture or behind a wall or ceiling.
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To increase the maximum number of exposures — limited to 24 or 36 frames when
using regular 35 mm film — this cartridge could hold up to 17 metres of 35 mm
film, equivalent to 450 frames.
The unit replaces the camera's rear door
and is attached to the camera body by means of two spring-loaded clips.
The film transport is driven by a
cogwheel
at the edge of the motor winder.
Move over the image to see the combination.
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This unit replaced the rear door
of the GSK and allows time and date to be superimposed on the picture.
It is based on a converted digital watch
and has its own internal miniature flashlight, driven by the flash socket
on the camera.
Embedded in the film pressure plate is a
miniature lens
that projects the image from the watch directly onto the rear side of the film.
Move over the image to see the combination.
➤ Read the manual
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Note that the 17 m film cartridge and the Data back unit are
mutually exclusive. They can not be mounted on the camera body
simultaneously, as they each replace the rear door of the camera.
There was also a combined cartridge/back unit.
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Manual controller
899 006
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When taking pictures manually, the exposure button shown in the
image on the right must be connected directly to the camera. Each time
the red button is pressed, an image will be taken.
The device can also be connected to the Remote Control Unit (RCU),
in which case the grey knobs can be used to shoot a series
of pictures. In that case, the remote control unit must be connected
to the camera using an interconnection cable.
➤ Pinout of the plug
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Automatic controller
899 003
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For stand-alone (unmanned) observations, this external control unit could be
used to (remote) control the camera, for example for taking pictures at
configured intervals.
In the latter case, the camera would usually be fitted with the
the 17 metre film cartridge, so that it would not run out after
24 or 36 exposures.
The unit can read the camera's light meter and can set the exposure time.
➤ More information
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Power supply unit
899 005
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The GSK camera must be powered external by 9V DC source,
such as the battery of a car or the mains power supply unit (PSU) shown
in the image on the right. The PSU has a fixed cable at its secondary side,
that ends in a 5-pin male DIN socket with the
same pinout as the camera.
A simple 1:1 DIN 5-pin male/male cable can be used to connect
the PSU to the camera. A suitable cable was supplied with the kit.
➤ Wiring details
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For situations where no mains power was available, the camera (or the
remote control unit) could be powered by the external battery unit shown
in the image on the right.
The case accepts 6 D-size battery cells of 1.5V each, that are series connected
to provide the 9V for the camera.
Move over the image to look inside.
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Power is distributed between the various parts of the SR-899 (GSK)
system by means of 5-pin DIN 180° male/male cables of various length. The image
on the right shows the short version.
Note that only three pins of the 5-pin connector are used, and that a 2-wire
cable is sufficient for power distribution.
➤ Wiring layout
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Thermal radiation detector
T-1.1
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The GSK can be further expanded by adding thermal radiation detector
T-1.1, shown in the image on the right.
It can detect a person up to a distance of 200 m, and can be
used to trigger the camera automatically.
Coming soon
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For covert photography from within a (portable) concealment, the Stasi used
special lenses: the so-called SO-series, or Sonderoptik
(special optic). Each lens was identified by a name (e.g. SO-3.1) and/or a
Stasi project number (e.g. 14601).
The lenses were designed to be able to shoot pictures through a small hole
in a concealment. Each lens came with an
adjustable diaphragm that could
be placed in front of the lens. In addition, each lens came with a selection
of fixed-aperture discs
that could be mounted in front of the lens instead of the
adjustable diaphragm.
Note that the first three lenses (35, 50 and 75 mm) are so-called
front stop lenses [4] of which the (virtual) entrance pupil (EP) [5]
is located in front of the first lens element. The EP position coincides
with the physical position of the externally fitted diaphragm, the fixed
aperture and/or the hole in the concealment through which the subject under
surveillance is photographed.
➤ Original product description
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SO-3.1, or project 14601, was a f2.8/35 mm 60° P-Flektogon lens with M36 mount.
It was fitted to the GSK by means of a M36/M42 adapter.
Supplied with adjustable and fixed diaphragms.
This lens is a so-called front stop lens in which the (virtual) entrance
pupil is located in front of the first lens element. This means that the image
is not cropped by the externally fitted aperture.
➤ Lens specification
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This lens is made of Thorium glass and produces radioactive radiation
with a strength of ~ 3µS/h.
This is ~ 30 times the background radiation.
SO-3.2, or project 14603, was a f2.8/50 mm 45° Biotar lens with M36 mount.
It was fitted to the GSK by means of a M36/M42 adapter.
Supplied with adjustable and fixed diaphragms.
This lens is a so-called front stop lens in which the (virtual) entrance
pupil is located in front of the first lens element. This means that the image
is not cropped by the externally fitted aperture.
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This lens is made of Thorium glass and produces radioactive radiation
with a strength of ~ 6µS/h.
This is ~ 60 times the background radiation.
SO-3.3, or project 14604, was a f3.5/75 mm 32° Tessar lens with M36 mount.
It was fitted to the GSK by means of a M36/M42 adapter.
Supplied with adjustable and fixed diaphragms.
This lens is a so-called front stop lens in which the (virtual) entrance
pupil is located in front of the first lens element. This means that the image
is not cropped by the externally fitted aperture.
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SO-3.4, or project 14605, was a f3.5/135 mm 18.5° Sonnar lens with M36 mount.
It was fitted to the GSK by means of a M36/M42 adapter.
Supplied with adjustable and fixed diaphragms.
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This adapter allows lenses with M36 thread to be mounted to a camera
with M42 thread, such as the GSK. M42 thread was widely used on Praktica
and Pentacon cameras in the 1970s and 80s.
M42 thread (Praktica mount) is still widely used today, and M42-adapters
are available for most modern cameras.
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For covert surveillance, such as in hotel and conference rooms, the Stasi
used the SO-3.5.1 pinhole lens,
developed by Carl Zeiss Jena.
This lens has M28 thread, for which an adapter to the camera's M42 thread
was supplied. As the lens has a fixed focal length, a set of range extenders
was supplied with the kit, providing enlargements of 1.5, 2 and 2.5 respectively.
➤ More information
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The GSK camera is based on the design of the Praktica EE2 35 mm SLR.
The enclosure (body) is very similar and a manual (mechanical) shutter release
knob is still available at the front. Bolted to the
bottom of the body is a relatively large motor winder, which forms a major part
of the design.
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Apart from a motor-driven winding mechanism, it also contains an electronic
shutter-release mechanism that is driven by an electromagnet (solenoid).
It is powered by an external 9V DC source that is connected to the
5-pin DIN socket at the side. The shutter can be released externally
by a hand unit or by an automatic control unit,
connected to the grey 7-pin socket.
One of the most innovative features of the GSK is the replacement
of the moving mirror by a semi-transparent foil. 1 Part of the light
is deflected to the viewfinder, whilst the rest reaches the film.
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For this reason, the mirror (i.e. the foil) no longer has to be flipped out of
the light path when taking a picture, like with most other SLRs.
As a result, the camera is much quieter than a regular SLR.
The image above shows the foil – placed under a 45° angle – as seen
through the lens port. Both the shutter (behind the foil) and the eyepiece
(above the foil) are visible simultaneously.
Due to the complex, compact and fragile nature of the motor winder,
we have decided not to take detailed pictures of the interior.
Instead we are showing several images that were taken by Detlev Vreisleben
when reparing a similar unit [1].
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Pentacon was not the first to use a static semi-transparent foil instead
of the moving mirror. In 1965, Canon introduced the Canon Pellix which
had the same feature. ➤ Wikipedia
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The output of the power PSU is available on a 5-pin 180° female DIN connector
at the end of a fixed cable. Below is the pinout when looking into the connector.
This is the same as the pinout of the 5-pin 180° DIN socket on the side of the
camera. A suitable 5-pin DIN male-male cable was supplied with the kit.
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- 0V (connected to 2)
- 0V (connected to 1)
- not connected
- +9V DC
- 17m cartridge end 1
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The GSK can be controlled remotely via the grey 7-pin female receptacle
at the side of the camera (just below the 5-pin DIN socket). This connector
– an RFT NS104 – accepts an NS105 male plug. The female socket has the following
pinout when looking into the socket on the camera:
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- Single exposure (connect to 7)
- Light meter output (1)
- Light meter ouput (2)
- +4.5V for light meter (input)
- Shutter open
- Shutter close
- Single exposure (connect to 1)
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In the simplest configuration, the handheld controller can be connected
directly to the camera, in which case only the red button can be used to
take a picture. Below is the pinout of the 7-pin male plug at the end of the
controller's cable, when looking into the plug.
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- Common
- n.c.
- n.c.
- Series exposure (connect to 1) 1
- n.c.
- n.c.
- Single exposure (connect to 1)
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Type SLR Purpose Surveillance, espionage, daylight, IR photography Manufacturer Pentacon Country DDR (East Germany) User Stasi (MfS) Format 24 x 36 mm Mirror Fixed, semi-transparent foil (low noise) Advance Low-noise motor drive Film Standard 35 mm Mount M42 (Praktica) Quantity 2000 units (est.) Power 9V DC
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SO = Sonderoptik (special optics).
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Distance between the rear end of the lens and the film (or image sensor).
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- Attaché briefcase
- Travel suitcase
- Shoulder bag
- Handbag
- Shopping bag
- etc.
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It is currently unknown how many GSK cameras were manufactured, but from the
surviving serial numbers, it is estimated that around 2000 units were made [1].
The serial numbers of the early prototypes (approx. 50 unit) were of the format
50xx, whilst production cameras were given 6xxx and 7xxx serial numbers.
Below is a non-exhaustive list of known serial numbers:
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5248· eBay (November 2021) 5561 eBay (November 2021) 6537· eBay (November 2021) 6877· Crypto Museum (Netherlands) 7002 Private collector (Germany) 7039 Highest serial number seen so far [1]
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A dot behind the serial number (e.g. 6877·) indicates that the device
was originally supplied with a control unit (Steuergerät)
with the same serial number.
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The GSK camera is known by the following names:
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- GSK
- Geräuscharme Spiegelreflex Kamera (low-noise reflex camera)
- SR 899
- 14101
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GSK
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Geräuscharme Spiegelreflex Kamera
{German) Low-noise reflex camera
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JO
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Justieroptik
German) Adjustment optics
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SO
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Sonderoptik
(German) Special optics
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Document kindly provided by Detlev Vreisleben [1].
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Document kindly provided by Detlev Vreisleben [1].
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Document obtained from BStU [2] and kindly supplied
by Detlev Vreisleben [1].
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Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes
der ehemaligen Deutschen Demokratischen Republik
(DDR) —
Federal Commissioner for the Records of the
State Security Service
of the former German Democratic Republic (GDR) —
officially abbreviated to BStU.
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Document obtained from BStU [2] and kindly supplied
by Detlev Vreisleben [1].
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© Crypto Museum. Created: Tuesday 16 November 2021. Last changed: Tuesday, 18 July 2023 - 07:54 CET.
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![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/027/thumbnail.jpg "image # 303727/027")
![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/028/thumbnail.jpg "image # 303727/028")
![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/026/thumbnail.jpg "image # 303727/026")
![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/027/full.jpg)
![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/028/full.jpg)
![Interior - motor drive unit - Copyright Detlev Vreisleben [1]](img/303727/026/full.jpg)
