Topping-out ceremony for the VTF

In early November 2017, the main frame for the Visible Tunable Filter (VTF) was installed at the large laboratory in the Jacob-Burckhardt-Straße 1 (JB1). All optical components of the VTF will be mounted to this complex structure. The steel frame extends over two floors, has an overall height of 5 meters and weighs about 2 tons. After the completion of the VTF in Freiburg, the instrument will be dismounted, packed up, and shipped to the Daniel K. Inouye Solar Telescope (DKIST) on the Hawaiian island of Maui.

Members of the VTF team and other KIS members from the „JB1 building“ during the topping-out ceremony for the VTF main frame structure.

CAD model of the VTF main frame as installed in the JB1 lab. A break in the ceiling is connecting the basement and the ground floor room. The dark grey displayed parts in the basement are a partial copy of the DKIST Coude floor structure were the VTF will later be built in. In red the so called “main frame” is shown. The upper and lower parts of the VTF structure are attached to it. The main frame also interfaces to the Coude floor via adjustable flange plates (the so called “clamps”) and steel beams (green) that are attached to Coude floor main beams. The brownish part is largest and with about 700 kg heaviest single module. The light path is illustrated in yellow. The light enters the VTF form the right side. Above the little tripod, the imaging lens will be mounted.

Delivery of VTF frame parts in front of the Jacob-Burckhardt-Str. 1 where the VTF lab is located behind the illuminated windows in the ground floor.

With a truck-mounted crane the heavy parts were lifted in front of the main entrance. From there the parts needed to be pulled manually on specifically build transportation frames with rolls. On their way to the lab they had to pass three doors – some of them needed to be dismounted.

Within the lab the modules needed to be turned and lifted to the correct position and then screwed together. The parts needed to fit to the previously aligned interface parts.

Before the integration of the main frame: Members of the VTF team align the parts („Clamps“) that interface between the main frame flanges and the duplicated DKIST Coude floor structure. The alignment as done to an accuracy of about 1mm within the 3D space.

The finally installed VTF main frame in the upper part of the VTF lab.

Die fertig aufgebaute VTF Tragestruktur im unteren Teil des Labors. Die weißen Träger im Vordergrund gehören zum Nachbau des DKIST Labors.


In Hawaii, the VTF will be mou ted on the rotating instrument platform of the DKIST. Due to its size,

the VTF will penetrate the platform's steel construction and reach into the mezzanine region beneath the platform. To guarantee th at our instrument will fit at the foreseen position, we built an exact copy of the corresponding part of the DKIST laboratory for the lab in Freiburg.

The VTF main frame consists of four modules, connected by flange plates. The exact orientation was marked with alignment pins; this allows to rebuild the structure on Maui with very high precision. The central part of the frame (red in the 3D drawing) was machined after welding on a large milling machine, to guarantee that all interfaces have a precision of b etter than 0.1 mm. The steel frame as a whole deviates less than 2 mm from the theoretical dimensions - an excellent result.

The steel frame had been manufactured at the company Winterhalter und Maurer located in Malterdingen near Freiburg, based on the sp ecifications provided by the VTF team, the manufacturing process was closely monitored by VTF engineers. Already during the design, we had to take into account that the frame had to go through narrow doors and had to fit into the tight laboratory. At the J B1, the margins were indeed only a few millimeters.