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    Astra IIIb: First Impressions
    From: Sean C
    Date: 2014 Mar 11, 13:10 -0700

    Had a chance yesterday to play around with my new Astra IIIb, my first metal sextant. Here's how it went:

    First, I was anxious to see if the shipping process had knocked anything out of alignment. The sextant was packed well enough, but I used to work for UPS and I know what goes on at shipping facilities. :o First order of business was to see if the index mirror was perpendicular. I used the caps from two "Koh-i-noor" technical pens as cylinders for the test. As far as I could tell, the top edges aligned perfectly. Next was supposed to be side error, but in my excitement I totally forgot about that. :) So, on to index error. I aligned one limb and then the other, subtracted the lesser and split the difference for an index error of 1!8 on the arc. As a sanity check, I set the micrometer drum to 0° 01!8 and saw that the images overlapped well enough, even without having checked side error. (There was just a sliver on either edge where there was no overlap.) I chose not to adjust out the index error for now.

    Next up: a few preliminary Sun sights before local noon to get a feel for the instrument. This thing is significantly heavier than my Davis! Arm fatigue will actually be a consideration now. But wow, what a nice, sharp and stable image! I don't see the edges of the mirror frames like I did with the Davis, I like that. The micrometer drum is quite a bit stiffer than my Davis. I'm not sure how I feel about that yet. I was comfortable with the amount of resistance my Davis offered. But I'm sure I'll get used to it. Overall, I'm extremely satisfied with the Astra's performance

    Here are the results from my first Sun sights:

    5 observations. Images were completely overlapped as opposed to using the limbs. I used my Davis artificial horizon as I had not yet had the time to determine the correction for the bubble horizon. After applying all corrections, the intercepts were: +1!7, +1!2, +1!9, +1!0 and +1!8. Not bad, IMHO!

    Unfortunately, the clouds didn't cooperate when LAN came around, so no noon sight just yet. I messed around with the bubble horizon a little and...holy moley this thing is tricky. Not impossible, but it will take some practice. I don't think I'll be able to use it too much for noon sights as I easily lose the hairline against the sun shades. Hopefully I'll get to do some testing during PM twilight today.

    I am so happy I got this sextant! Now...I begin saving for a chronometer! ;)

    -Sean C.
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