20th c. Askania Tu400 theodolite

The Askania Tu400 theodolite
Figure 1: The Askania Tu400 theodolite
This Askania Tu400 theodolite was part of a large donation to my collection together with a 1962 Wild T2, a 1969 Wild T2E theodolite, a 1951 Wild N2 level, a 1960s Jenoptik Koni 007 level, a 1960s Zeiss Opton Ni 2 level, a 1956 geodetic sextant, and various accessories.

Provenance
The above mentioned group of instruments once was part of the set of instruments used by the field organisation TGTW of the Survey Department (Meetkundige Dienst, 'MD' in short) of Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and the Environment, responsible for the design, construction, management and maintenance of the main infrastructure facilities in the Netherlands).

The registration number "AS1" (see figure 15) indicates that this was the first (and perhaps only?) Askania Tu400 bought by that department.

The field organisation TGTW was closed in the early 2000s and in 2008 the instruments were donated to my collection.

Development
The Tu40 is an instrument with glass circles and an optical reading mechanism, clearly influenced by the instruments of Heinrich Wild like the ThI he developed for Carl Zeiss and the archetype T2 he developed later within his own firm.

The link with Carl Zeiss is obvious as the base of instruments like the Carl Zeiss Th42 is interchangeable with the Askania tribrach thanks to their DIN 18719 stub and socket joint (see figure 13 and figure 14). The carrying dome shows similarities to the ones used by Wild Heerbrugg (see figure 4), although the one from Askania is considerably wider at 190mm outer diameter (measured halfway up the dome).

The Tu400 was first advertised in the Netherlands at the end of 1956 as the "Theodolieten Model 1956" (earlier advertisements only show levels and non-automatic theodolites). It could be ordered with an astronomical (inverted view) or geodetic (erect view) telescope and with either sexagesimal or centesimal divided circles.1

The Askania Tu400 from the other side.
Figure 2: The Askania Tu400 from the other side.
Accuracy
According to the 1956 advertisement it could be read to a single arc second or 0.0002 gon and estimated one digit further. The 1957 Askania brochure listed the Tu400 as an instrument for triangulation, traversing and field astronomy (see figure 17).2 In 1967 a degree version of the the Askania Tu400 was listed as the K&E KE-2(e) 'One-Second Theodolite' in the Keuffel and Esser catalogue (see figure 18).2 That both instruments are the same is confirmed by Deumlich in his Instrumentenkunde der Vermessungstechniek (1972), p. 134.

On the instrument in my collection both the 90mm horizontal and 70mm vertical circles are divided in gon (400 divisions in a full circle) and - as indicated in the catalogue and brochure - can be read down to 0.0002gon (about 1 arc second, see figure 10) and estimated one further decimal. The instrument has a pendulum type compensator for the vertical circle (see figure 19).

Notes

[1]: Advertisement in: Tijdschrift voor Kadaster en Landmeetkunde, 72e jaargang, nr. 6, (1956), after p.408.
[2]: Many thanks to John Vossepoel for sending me these pages.

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

The Askania logo and serial number.
Figure 3: The Askania logo and serial number.
 
The Tu400 with its container and sun shade.
Figure 4: The Tu400 with its container and sun shade.

Coarse aiming is done with a visor and bead.
Figure 5: Coarse aiming is done with a visor and bead.
 
The Tu400 came with its original sunshade.
Figure 6: The Tu400 came with its original sunshade.

Adjusting the horizontal circle is done using this push-rotating button with safety release.
Figure 7: Adjusting the horizontal circle is done using this push-rotating button with safety release.
 
The optical plummet consists of a double concentric draw tube.
Figure 8: The optical plummet consists of a double concentric draw tube.

Illumination of both circles is done using a single rotating mirror.
Figure 9: Illumination of both circles is done using a single rotating mirror.
 
Left the horizontal circle reads 384.1277g. Right the vertical circle reads 284.4042g.
Figure 10: Left the horizontal circle reads 384.1277g. Right the vertical circle reads 284.4042g.

The inverted view through the telescope reveals four stadia hairs and a central cross.
Figure 11: The inverted view through the telescope reveals four stadia hairs and a central cross.
 
The optical plummet has a double circle reticle.
Figure 12: The optical plummet has a double circle reticle.

The tribrach connects to the yoke with a Zeiss type stub.
Figure 13: The tribrach connects to the yoke with a Zeiss type stub.
 
Electricity for artificial lighting is passed to the yoke by a sliding contact.
Figure 14: Electricity for artificial lighting is passed to the yoke by a sliding contact.

The two layers of the tribrach have braces to avoid rotation.
Figure 15: The two layers of the tribrach have braces to avoid rotation.
 
The horizontal 20"/2mm vial of the Askania Tu400.
Figure 16: The horizontal 20"/2mm vial of the Askania Tu400.

The Askania brochure.
Figure 17: The Askania brochure.
 
The K&E brochure showing the Askania Tu400.
Figure 18: The K&E brochure showing the Askania Tu400.

A 1958 ad showing the Tu400 compensator.
Figure 19: A 1958 ad showing the Tu400 compensator.
 
The logo remained unchanged (inset) over the years and is still used on their watches.
Figure 20: The logo remained unchanged (inset) over the years and is still used on their watches.

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 1963/76 Wild T2 - DI3S 1963 Wild RDS 1966 Kern DKM2 1969 Wild T2E 1976/79 Wild T2 mod - DI4 1990 Wild T2 mod - Di1000 20th c. Askania Tu400