Sextant mirrors
There are a total of three different horizon mirrors for our sextants:
- Traditional split-view mirror
- Full-view mirror
- Clear-view mirror
The type of horizon mirror is partly already predefined in our sextant models, as e.g. a Schüler double prism cannot be used with a split-view mirror.
Traditional split-view mirror
It all started with the split-view mirror, which is why we also speak of a traditional split-view mirror. This mirror is fully mirrored on one half.
Advantage:
- A maximum brightness of the horizon view for twilight observations
- The edge of the mirror simplifies the vertical orientation of the sextant
Disadvantage:
- Star and horizon are separated
- The measurement is only possible if the direction to the star is kept exact
- "Swinging the arc" to find the base point on the horizon is difficult.
Full-view mirror
The full-view mirror is fully half-silvered and thus semi-transparent.
You can look halfway through the mirror in horizon direction and the other half of the viewing beam is mirrored in index direction.
Advantage:
- The star can easily be kept in the field of view in turbulent seas.
- Star and horizon are always in view at the same time
- The observation is simplified
Disadvantage:
- The brightness of the horizon image is reduced due to the semi-transparent mirror that can make twilight observations more difficult
Clear-view mirror:
The clear-view mirror was developed by Cassens & Plath. The central vertical part of the mirror is half-silvered and thus semi-transparent.
The sides are not mirrored and offer a clear view of the horizon.
Advantage:
- Clear view of the horizon
- Star and horizon are simultaneously in view in the centre
- Good light conditions at sea by day and night
- Combines the advantages of the traditional split-view and full-view mirrors
- Observations are simplified
