The stereoscopic rangefinder OEM-2 (first trial of english edition)

Literature: NVA Service Instruction A256/1/327 - OEM-2  - Description and Use.

The Carl Zeiss Jena OEM-2  is an optical rangefinder which works by stereoscopic principle with moveable sights.
OEM-2 is the abbreviation for "Optisches Entfernungs Messgeraet Nº2". It served with the Artillery-observers of the army of the former communistic German Democratic Republic, NVA (Nationale Volks Armee).
Therefore it reflects the latest development of stereocopic rangefinders made by Carl Zeiss in Jena.
A characteristic of this construction is the biaxial sightkollimator,  which makes the sight staying adjusted in cases of athmospheric influences like partial warmings of the housing by sun, which may cause changes of the angle of the mirrors or prisms.

This way of construction generally marks the way, Carl Zeiss Jena made their stereoscopic rangefinders.  It finally enabled the construction of rangefinders like EM-61 or EMK-04 at all, with its special problems that consisted of inaccuracies of the central joint.
Development time of the OEM was approximately from 1969 to 1976.

It was made for
- Artillery observation
- determination of linear and polar coordinates of targets or hits.
- determination of range and horizontal and vertical angles.

Notice: The artilleristic circle of eastern army systems is devided by 6000 units (1/6000
 "Mil-Strich") instead of 1/6400 like it is used in NATO countries. There is no compatibility.

Mounted on a special elevator-device, OEM-2 was used directly at the mobile artillery observation point SPW 60 PB, (picture shows not the observer´s vehicle but a command version. The observation vehicle is equipped with a turret and a 14,5 mm KPWT heavy machinegun . Its outer appearence doesn´t differ from the "normal" BTR-60 - it is just an example)  a special version of the famous russian 8X8 armed personnel carrier "BTR 60".
Therefore OEM-2 can be compared with a 30 cm high periscope.

In normal use it was mounted on a strong tripod out of the vehicle.

Now have a look at some pictures:
 

An OEM-2 in its transport- and storage case. In the upper half case we recognize the pigeonholes in which small supplies are stored. This store was called "EWZ-Satz" - which means spare- tool and supply-part kit. On the left hand: (from top) batterycase for 5 NiCd accumulators or 4 normal alkaline-cells size D. In case of using alkaline batteries, take the dummy, which is located in the little tin-box under the batterycase. Right next to the batterycase and tin-box we can see the cables with different joints, fitting  different devices like power supply, batterycase and rangefinder. The lower pigeonhole on the left includes the power supply LG-OEM2 (Lade- und Fremdeinspeisegeraet). This powersupply enables the use of 220 V AC; 24 V DC and 12 V DC, you can find on tanks ;-) , trucks and cars. Output is 6 V DC with 300 mA constant, which enables batterycharging with the powersupply. On the right hand: Here we find cleansing and decontamination utilities, such as empty bottles, which were to be filled with decontamination agents in case of war - which fortunately did not take place. The grey flat bag in the middle contains a little book which includes the diary of use and maintenance intervals. Here you can get information if your OEM has already been used or not. Additionally the conditions of desiccant cartridges are documented here. In the lower case right next on the right-hand side of the OEM we see a double face canvas hood to protect the OEM from direct sun or rain. You can turn the white inside out to get winter-camouflage

 

OEM-2 tripod with inserted telescope-legs. The black rubber-handles are to be used for fine-horizontation.

Some technical data:

Weight of OEM-2: 27,5 kg;

Weight of tripod: 9,6 kg;

Weight of transport- and storage Case (with all supplies included): 32,5 kg.

Former salesprice, the NVA had to pay: 138.000,-- M (I have heared of - but I haven´t seen this information yet)

Required current: 6 V DC  (Polung unbedingt beachten).

OEM-2 side of okulars and switchpanel

Above the right ocular we can see the dark round UV-filter for infrared-reconnaissance. It can be switched on by using the little lever to the right of the ocular. It is an infrared-sensitive screen, which shows a pale brown light if it is hit by IR-rays of the spectral area military IR-devices use. You can easily test it with your TV-remote control. At the lower side of the optical base we can see the buttons for highth- correcture of the sights. On the right of the T-like-stucture of the OEM-body  the measure-wheel is located.  The knob on its top triggers the electrically powered pendula of the sight in case of beeing pushed. The knob under the right arm which is marked from 1 to 6 is to change the amlitude of pendula. The little two grey, round structures directly on top of the switchpanel are containers which can be removed by pulling them straight to the top. They should include cleansing equipment and a little spare-lamp. On the right hand of "the U"  we can see the buttons to zero the display of the mechanical X-Y-coordinate calculator. It counts the "hm" (hundred meter).  The little black knob inbetween is the socket for the illumination lamp. Any movement of the OEM (turns, variation of sights or changes of vertical angle) will automatically be registered by the calculator´s gear. This is something like  "high-mechanic"! No danger of beeing disturbed by NEMP (nuclear electromagnetic pulse). The lens on the ground is to see the horizontal angle in military angle units 1/6000.

OEM-2 optical base objective´s side. All little windows for daylight-illumination of sights are opened - also the little window for the wide-angle objective. The left objective is hidden behind the grey-filter to darken the view-field to higher the contrast between the object and the sights during daylight-observation. In dawn and darkness you may close the windows and work with the electrical illumination.