Cassens & Plath Sextant HORIZON ULTRA black, Full-view mirror

‌The HORIZON ULTRA is a specialist for solar observations with its polarised shadow lenses and the double prism pupil.

You can choose between a rough case and a wooden case. You can also have your sextant engraved with your name on request.

Please note: The artificial horizon does not fit into the rough case together with the sextant. Here we recommend the wooden case, in which an additional holder is attached.

Sextant frame and construction

The frame is made from a 5.5 kg brass plate, which is milled to produce a frame weighing approx. 0.6 kg. Once the milling work is complete, the frame is heated in a furnace, straightened, ground and engraved. The individual components are then assembled. Once completed, the sextant consists of over 100 individual parts, most of which are manufactured in-house. All components are assembled and adjusted by hand. Each sextant is tested after manufacture and a quality certificate is issued.

Full-view mirror

The sextant is equipped with a full-view mirror. It is half-silvered and therefore semi-transparent, which means that half of the mirror can be used to look in the direction of the horizon, while the other half reflects the line of sight in the direction of the index.

This has the advantage that the celestial body can be kept in view more easily even in rough seas and that the celestial body and the horizon are always in view at the same time. This simplifies measurement. The partially transparent mirror coating slightly reduces the brightness of the horizon image, which can make observations at dusk more difficult.

Schüler double prism

The Schüler double prism is only installed as standard in the HORIZON ULTRA. It is located in front of the shadow glasses in the horizon direction. Can only be used in combination with a full-view mirror. The glass is specially ground to block out the vertical area in the centre of the horizon sighting beam. This is advantageous for solar observations for two reasons: This eliminates sun reflections on the water surface and prevents measurement errors caused by glare. In addition, any tilt of the sextant can be clearly recognised as a step in the horizon.

Polarisation shadow glasses

In addition to the Schüler double prism, the polarisation shadow glasses are also only installed in the HORIZON ULTRA. One lens is located in the horizon direction and one in the index direction. The polarisation shadow glasses allow the brightness of the celestial body to be adjusted continuously by turning the lens. This means that no extra shadow glasses need to be added or removed during observation, making it easier to keep the celestial body in the field of view.

Combined kimm depth and index adjustment

The HORIZON ULTRA sextant has a combined depth of view and index adjustment on the drum screw. There is an extra scale on the drum screw where the index error can be corrected, so you do not have to take the error into account in further calculations. You can also correct the index error on the horizon mirror. Note: The kimm depth adjustment must be carried out before the index correction. The kimm depth adjustment allows the eye level to be preset independently of the index error and does not need to be taken into account in further calculations. In practice, however, the kimm depth is rarely adjusted. The left scale is for kimm depth adjustment and the right scale is for correcting the index error.