Hi Marty:
I’m curious to know if you have an American transit or a theodolite. The
standard American transit was a fine rugged instrument with horizontal and
vertical vernier scales for reading (turning) and measuring
horizontal and vertical angles. Europeans developed more accurate and
somewhat less rugged theodolites which generally could record/measure with
greater precision and accuracy. Optics were better. Gurley is one American
manufacturer of transits put out of business by the Japanese and the Swiss.
My recollection is the best you can measure a vertical angle with a
transit, without doubling or more the measurement, is 0.5 minute of arc ( and
you go blind trying to read with the pocket magnifier) .
If you have a theodolite, you should be able to measure to within 5 or 10
seconds of arc . I used my theodolite to measure Hs for the moon, any time of
the day. At near dusk, precompute Vega,Venus, Sirius, Deneb, Jupiter,
etc. With the magnification, these will jump out at you “like a “
flashlight”. Be careful to precisely set and level the instrument, and
don’t “hang” on the scope or put yours hands on the legs. Compare your results
with sextant results. Measure dip and use the measured dip with your
calculations.
You will get many questions from onlookers. Kids will want to look.
Regards,
Bruce
Sent: Saturday, January 17, 2015 12:51 PM
Subject: [NavList] Any tips for using a transit for celestial shots
on land?
Somehow I wound up with three engineer's transits, that I have been taking
celestial shots with, night and day. So far I have been unable to see any stars
or planets during the day. Any tips would help.
A few things I have found.
I use two adjustable neutral density camera filters adapted to the front of
the transit scope for sun shots. It works great since you can fine tune the
amount of shading from 2x to 400x. They can be had very cheaply on eBay.
Since you can't see the black crosshairs at night, I find that a keychain LED
light shown in the front of the scope, illuminates the hairs and the star is
still visible.
It's tough to get the stars into the field of view of the 26x scope, so I
fashioned some crude rifle sights on the scope and that helps greatly.
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