CASSENS & PLATH BOBBY SCHENK Sextant Handhabung Seite 20

Instructions
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Design
Index shade
glasses
Horizon mirror
Mirror adjustment
screw
Horizon shade
glasses
Limbus, arc,
graduated scale
Drum with
minute scale
At its lower end the sextant frame carries the arc or limbus with a graduation from -5° to +125°. An
angle of more that 90° can be used to check an unusual horizon dip. The alidade or index arm is
pivoted to the frame by means of a specially designed bearing that grants a minimum of slack.
Attached to the upper end of the index arm is the index mirror. The lower end of the index arm
supports the graduated drum with knurled knob and tangent screw, the vernier, the lever and the
index mark to read off full degrees. The drum has scale units of 1`. Decimal minutes may be read
from a vernier scale.
The telescope is detachable, and is fixed by a knurled screw to the body of the sextant.
The eyepiece is rotatable for focussing. The 4 x 40 mm optical system grants sufficient brightness
for twilight observations as well as enough magnification for coastal horizontal angle
measurements.
The horizon mirror is mounted in front of the telescope. In front of this a set of 3 differently tinted
horizon glasses (circular) is installed to dim the sun´s reflection on the water surface. A set of 4
differently tinted index shade glasses (rectangular) is located between horizon and index mirror.
These shade glasses are for light dimming of the doubly reflected celestial body (sun). In order to
ensure equal brightness of both images -especially during sun observation- the tinted glasses are
all of systematically graduated transparency and can be moved into the path of light singly or in
any required combination from either set of filters. All shade glasses stop transmission of non
visible light so that no harmful effects will be caused when looking into the sun through these
shade glasses.
The reverse side of the frame carries the handle with batteries for illumination and the legs.
The full-vision mirror extends the field of vision along the horizon by 95 % compared to the
traditional mirror, and, depending on the wavelength of the light, meets with the needs of the
human eye concerning the light reflection/transmission ratio.
The traditional split view horizon mirror, on the other hand, allows direct, not attenuated horizon
view. This can be advantageous under poor visual conditions like in twilight. The vertical
silver/transparency limit makes the vertical finding at observation easier.
BOBBY SCHENK Sextant
Index mirror
Mirror adjustment
screw
Telescope
Telescope
focussing
Sextant frame
Alidade, Index
arm
Lever