Re: [APML]: barndoor tracker question

[DROWESMI@aol.com]

Jim Fedina wrote:

>Is it that the barndoor drive stays pointing at the NCP and you
>turn the camera only? I'm trying to think of how that theory would work
>as I am writing this.

Jim:

You've got the picture.  Leave the barndoor tracker accurately pointed at the
NCP and move the camera to your subject.  I do this with a ball joint that I
picked up for cheap at a used camera store.  I mounted the ball joint on the
moving board and the camera screws right into the head of the ball joint (I
can't get access to the whole sky with this but it's good enough.)  I got some
nice shots with this arrangement using a 200 mm lens at f/4 with 5 minute
exposures.  The trick is to very accurately polar align which isn't easy.  See
the archives for polar alignment help with this mount.  If you want to quickly
align this gizmo, first accurately mount a finder scope so that it points
along the polar axis.  In the field you then adjust the alt-az arrangement so
that the finder points to the NCP.  My set-up looks like it came right out of
a Rube Goldberg (sp?) drawing.  What fun!

I found that some fiddling with this setup is required.  Not all your shots
are going to turn out well.  Try shorter and longer exposure times and see
what happens. 

Dave Rowe
Torrance, CA