NavList:

   

Reply

> Bill, you mentioned that you were using your Astra IIIb on a tripod.  Can
> you explain your setup?  We had discussed tripods last year on the list.  I
> found an old camera tripod, but never got around to working out the
> attachments.

No problem Jim.  In fact just sent it to an off-list request from Australia.

I use this setup for calibration purposes only, where something better than
a almost-steady hand, a gut feeling, and a prayer are required.  I am
using photo gear I have around and a few other items I use in the studio.
JPEGs of hardware attached as a few pictures are worth a thousand words.

Ingredients:

Husky Tripod

Bogen (Manfrotto) Super Clamp #035, list $33 (street $24)
NOTE:  This clamp can also be used with Ram-Mount's line of products to
mount a GPS, Palm Pilot etc. almost anywhere on a boat. bike etc.

Lowel Interlink, list $30 (street $22)

Lowel Stud, list $15 (2 may come with the Interlink, I am not certain.)

Crafsman (Sears) #3984 Universal Protractor, $10 (This is a round dial with
a gravity needle in it.  I think model number has changeg over the decades.
Appears to be used by framers for roof pitch) Any small level that makes
contact with the sextant frame and clears the arc would work.

Empire Polycast Post Level  (A couple of bucks at Menards, Lowes, Builders
Square etc.  Modified by gluing cardboard on the inside surface for uniform
contact with tripod tube)


Method:

Set up tripod to aprrox. eye level with approx. 9" of center column raised.
Do not fully extend upper leg adjustments.  Leave 3" or so for later
adjustment.

Lowel stud has a female tripod thread on one end.  FIRMLY thread this on the
tripod-head camera-mounting male bolt.

Attach Interlink to stud from tripod head.

Attach Super Clamp to horizontal stud.

NOTE.  Most tripod heads have two adjustments.  One for lens up/down
(vertical) and one for leveling camera to horizon (horizontal).  Roughly
align the Super Clamp so once the sextant handle is clamped in it you can
raise of lower the angle of the scope with the vertical head adjustment, and
get it plumb with the horizontal head adjustment.

Plant tripod in desired location with one leg facing the primary azimuth,
leaving the reaming two to the sides of the observer.

Attach post level to tripod column so one side is parallel to the forward
leg direction (towards azimuth), the other parallel to a plane described by
the feet of the two lateral legs.

Adjust a lateral leg to get level on its plane/axis.  Adjust the forward leg
to get level on its plane/axis.  Repeat once or twice as needed until column
is vertical on any axis.

Mount sextant handle in Super Clamp (jaws are padded), experimenting to get
best contact with least pressure on the handle from the clamp.

Using stud knobs, adjust orientation of sextant body so it is
aligned/parallel to the head's vertical axis adjustment.

Using head horizontal adjustment and universal protractor, adjust until body
of sextant is perfectly vertical.

There you have it.  In theory, if everything is aligned, you can pan left or
right without changing elevation, and change elevation without getting the
sextant out of plumb.  In theory, practice matches theory.  In practice it
does not.  When panning and/or changing scope elevation more than a smidge,
double check with the universal protractor to determine the sextant has
remained plumb.

Hope that helps,

Bill

Sources, or just Google "Bogen Super Clamp" or "Lowel Interlink."

http://www.ggvideo.com/low_clamps.htm

http://www.bogenimaging.us/product/templates/templates.php3?sectionid=221&it
emid=344

File:

File:

File:

File:

   

Reply