1966 Kern DKM2

The Kern DKM2.
Figure 1: The Kern DKM2.
This theodolite arrived in my collection in 2015. It came from the collection of the land surveying department of the Hogeschool van Utrecht, but is now on long term loan in my collection. Previously a Kern E1 electronic theodolite entered the collection.

When Heinrich Wild left Wild Heerbrugg he joined Kern Aarau where he continued designing theodolites. The Kern DKM2 was meant to be the competitor of the Wild T2 and thus has similar specifications. The DKM2 shows features well known from Wild's original designs while working in Heerbrugg, but at the same time this instrument shows that his ideas kept on evolving while working at Kern in Aarau.

Old design features known from the Zeiss Th1 and archetype Wild T2 include:
  • The bead type visor for coarse aiming;
  • Smallest possible dimensions and weight (it is smaller than the period T2, see figure 11);
  • Convenient manipulation;
  • Insensitivity in respect of transport, rain and dust;
  • Combination of diametrically opposed parts of the circle, observed in one eyepiece;
  • Fully enclosed circles;
  • Micrometer for direct reading of the arithmetical mean;
  • Use of glass circles;
  • The anallactic telescope with internal focusing;
  • Coincidence vial;
  • Cylindrical main axis;
  • Dust-tight arrangement for foot screws.
In addition Heinrich Wild added a few new features:1
  • A single mirror to illuminate both circles (see figure 5);
  • Vertically placed knobs for the foot screws (see figure 6);
  • Double graduated circles (see figure 15);
  • Ball bearings of the vertical axis at maximum radius for more stability (see figure 14);
  • Anti reflection coating for sharper contrast.


The Kern DKM2 from the other side.
Figure 2: The Kern DKM2 from the other side.
The characters "DK" in DKM2 indicate that this is a Doppelkreis (double-circle) theodolite.2 Doppelkreis instruments are equipped with double graduated circles (see figure 15), where the surface on the inside of the circle is graduated coarsely and finely on the outside. By superimposing them on top of each other the former serves as a visual reference for the latter.

The character "M" in DKM2 indicates that this model is equipped with a micrometer.3 Like the Wild T2 the micrometer can be viewed through the micrometer reading telescope next to the main telescope of the instrument.

Accuracy4
The specimen showed here has centesimally divided circles. The diameter of them is 70 millimetres for the vertical circle and 75 millimetres for the horizontal one. They can be read directly to 2cc (0.0002 gon or 1" for the sexagesimal version) and estimated to 1cc (0.0001gon or 0.1" for the sexagesimal version).

The telescope has a 30 times magnification and a 45 millimetres diameter objective. It produces an inverted view. By default the DKM2 was equipped with single lines for both the vertical and horizontal cross-hairs. Customers could choose from eight different types of reticles, the specimen shown here has model G etching (the Zeiss Th1 type of reticle).5

The vials have an accuracy of 20" per 2 millimetres run. The one for the vertical circle is equipped with a coincidence reading system as may be expected from an instrument designed by Heinrich Wild.

The instrument weighs 3.6 kilograms, with an additional 1.8 kilograms for the container.

The instrument
This particular DKM2 once belonged to the Hogeschool Utrecht where it served educational purposes. Thanks to that it is in pristine condition. It came complete with its original container in which the the tools are still present (see figure 3, figure 9 and figure 10).

Notes

[1]: Kern Aarau, 'Doppelkreis-Theodolite', in: Kern & Co. Ag. Aarau, Schweiz: Prospekt DK 562, (Aarau, before 1964), pp.2-6.
[2]: idem, p.2.
[3]: idem, p.3.
[4]: idem, p.7.
[5]: idem, p.33.

If you have any questions and/or remarks please let me know.

The Kern DKM2 came in its original container.
Figure 3: The Kern DKM2 came in its original container.
 
The Kern Aarau logo and serial number. Above the logo the electrical connector can be seen.
Figure 4: The Kern Aarau logo and serial number. Above the logo the electrical connector can be seen.

The coincidence vial of the Kern DKM2.
Figure 5: The coincidence vial of the Kern DKM2.
 
The vertical oriented tribrach screw (left), the horizontal setting screw (right) and optical plumb.
Figure 6: The vertical oriented tribrach screw (left), the horizontal setting screw (right) and optical plumb.

The DKM's main vial. NV Handelsvereniging Hagen was the Rotterdam retailer.
Figure 7: The DKM's main vial. NV Handelsvereniging Hagen was the Rotterdam retailer.
 
On the inside of the vertical circle housing a bead type visor assists in coarse aiming.
Figure 8: On the inside of the vertical circle housing a bead type visor assists in coarse aiming.

The DKM2 on its original base. The two latches fold back to hold the instrument in place.
Figure 9: The DKM2 on its original base. The two latches fold back to hold the instrument in place.
 
The container still has the original tools and a leather chamois.
Figure 10: The container still has the original tools and a leather chamois.

The 1966 Kern DKM2 (left) compared to the 1962 Wild T2 in the collection.
Figure 11: The 1966 Kern DKM2 (left) compared to the 1962 Wild T2 in the collection.
 
The view through the telescope is inverted, the reticle is reminiscent of the Zeiss Th1.
Figure 12: The view through the telescope is inverted, the reticle is reminiscent of the Zeiss Th1.

The optical plumb of the DKM2 is a simple cross.
Figure 13: The optical plumb of the DKM2 is a simple cross.
 
The vertical axis of the DKM2, showing the ball bearing in red and circle in blue (added colouring).
Figure 14: The vertical axis of the DKM2, showing the ball bearing in red and circle in blue (added colouring).

A schematic diagram of the Doppelkreis (double circle) method of the DKM2 (added colouring).
Figure 15: A schematic diagram of the Doppelkreis (double circle) method of the DKM2 (added colouring).
 
The vertical circle (left/top) reading 100.5916gon, the horizontal circle reading 255.9607gon.
Figure 16: The vertical circle (left/top) reading 100.5916gon, the horizontal circle reading 255.9607gon.

Surveyor's crosses Geodetic Sextants Theodolites Total Stations Levels Standards Tools Firms
19th C. SDL 1919 K&E 1926 Zeiss RThII 1924 Zeiss Th1 1929 Wild T2 1937 Wild T3 (astronomic) 1939 Wild T3 (geodetic) 1943 CT&S Tavistock 1948 Wild T1 1952 Wild RDH 1956 Wild T0 1961 Wild T1A 1961 Wild MIL-ABLE T2 1962 Wild T2 1963 Wild RDS 1966 Kern DKM2 1969 Wild T2E 20th c. Askania Tu400 1990 Wild T2 mod