Alan,
I use a mirror AH exclusively
and have experienced the same issue you mention. In every case it
has turned out that the sextant was off vertical so the path of the sun's
reflection in the AH did not cross my field of view. Some exploratory
"rocking" is often needed. It is also helpful to
take a guess at the altitude and pre-set the angle of the index arm to
twice this guess. That allows you to rock without having to combine
rocking with turning the micrometer drum. Even if your guess
is just close, it may bring the glow of the sun's reflection into view,
allowing you to 'dial it in'.
Just some general mirror
AH advice; you must have a very accurate level to get good results.
The string levels you mention are not nearly accurate enough. They
are probably in the neighborhood of several tens of minutes and you need
fractions of a single minute. There have been many posts about
this issue. In addition, you may need to add some extra filtering
in front of the horizon glass to decrease the sun's brilliance.
The normal horizon shades are not intended too look directly at a reflection
of the sun. There are films for this purpose, again mentioned in
previous posts.
Good hunting, Randy
Randall F Morrow PT
Kern County - Bakersfield
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I have two of the things, one being the Davis AH, people
here are likely familiar with this device.
I also have a home made AH, first surface mirror, 10"
x 10", on a levelable base. I level the assembly using a couple of
string levels and reasonably fine leveling screws 120 degrees apart.
This afternoon, I'm in the Pittsburgh area, I did a couple
of sun shots with the Davis AH sitting on the ground. IE was 1.8 Min On
Arc. Measured angles were 90 D 48 Min, and 90 D 25 Min, without correction.
Time was around 1430, Eastern Daylight Savings Time. Nothing further wad
done, that is the sights were not reduced.
I next brought the mirror AH out for an airing. Setting
is on the ground, leveling the unit, I saw reflected sun, but could not
find sextant sun, that would be the sun that moves when the index arm is
swung.
I next tried setting the mirror ah on an elevated surface,
using an ironing board, which is about 40" high. After leveling the
assembly, I tried a sun shot, rocking the sextant while swinging the index
arm. Reflected sun was visible, but alas could not find the sextant sun.
I assume that I'm doing something wrong, but cannot figure
out what that might be. Anyone here got any bright ideas or suggestions?
Thanks in advance for same.
Alan
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