We sell what we
know, not everything
The Astra IIIB
has somewhat revolutionized celestial navigation.
Never before has such a high quality, accurate metal
sextant been available at such a low price. Over
21,000 sextants of this model have been sold in the
US alone in the past 23 years; far more than any
other serious sextant. Its popularity has spread
throughout the rest of the world as well, making it
the the most recognized (and supported) sextant
worldwide.
Its low price,
excellent optics, and choice of horizon mirrors and
other accessories makes it the perfect selection for
beginners. Yet, we know several professional
navigators who prefer the ASTRA IIIB merely because
they can leave their expensive models at home
without sacrificing noticeable accuracy. The Astra
IIIB is made by the Changzhou Celestaire Instrument
Co. in China, with whom Celestaire is
joint-ventured, and it is produced in accordance
with our specific quality guidelines.
Construction Details
The frame is
made from lightweight aluminum alloy which resists
corrosion. Aluminum alloy is not new to sextant
construction. It has long been used by many
manufacturers for lightweight versions of their
heavier brass or bronze sextants in order to reduce
arm fatigue and unsteadiness among infrequent users.
The sextant is electrically lighted by an LED on the
arc and drum.
The Astra IIIB
is considered by many to be the easiest sextant to
use. Its light weight and excellent balance makes it
a pleasure to hold and makes sights easier to take
under dynamic weather and sea conditions. Even
reading the sextant is easier under low light
conditions by having white degree marks against a
black background as opposed to scribe marks on a
brass arc.
The index
mirror is rectangular in shape and is the same size
as used more expensive sextants. This shape allows
more aspect of the mirror to be available for high
angle sights. This means the sextant does not have
to be held as steady for them. An index mirror
upgrade kit is available for older models having
smaller, round, index mirrors. It comes mounted in a
rectangular frame and has instructions for easy
installation.
We are
impressed with the degree to which each component of
the sextant is tested. For example, each mirror and
shade glass is tested for perfect flatness by the
Fresnel diffraction pattern method. The sextants are
assembled and tested in a clean, professional,
environment. Random units have been tested by us and
several professional navigators, with results that
rival the most expensive German and Japanese models.
Features
The ability to
quickly and economically change the type of horizon
mirror is an attraction of this sextant to many
navigators. This is because whole horizon mirrors
are generally preferred by beginners who later may
wish to change to a traditional mirror as
proficiency is attained (see "Selecting
A Marine Sextant").
Maintainability is appreciated by schools and other
groups who because of heavy usage need inexpensive
replacement parts due to the threat of student
mishandling.
Included and Optional Equipment
The sextant
has LED lighting of the arc and drum powered by two
standard size AA batteries (not included) which
install in the handle. It comes in a varnished
wooden case, with instruction book, certificate of
accuracy, and adjusting wrench. Case external
dimensions are 6.5 x 13 x 11 inches. It includes a
3.5x40 monocular telescope as standard equipment.
Optional
accessories include a 7x35 prism telescope, a
slip-on rubber eyecup for use while wearing glasses,
and a zero-magnification sight tube. Changing
mirrors is done quickly by means of two easily
manipulated screws.
SPECIFICATIONS
Arc |
-5° + 130°, radius 153mm |
Accuracy |
± 20", throughout the
arc |
Micrometer Drum |
1' scale, vernier to
0.1' |
Horizon Mirror |
51mm diameter |
Index Mirrors |
56x42mm |
Shades |
4 index - 3 horizon |
Weight |
2 lbs., 10 oz |
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