|
Hi Michael:
I don't have much experience with a
barndoor tracker, having made one (roughly) and almost immediately moved on to a
driven mount. However, I would guess that unless you have machine tools
available, the marine plywood will be much more suitable. Aluminum (aluminium)
requires metal working tools (or junking the saw blade after using a
wood-cutting blade) and is HARD work if you're cutting by hand. Acrylic plastic
(Perspex) is brittle and requires care to avoid splitting, especially when
drilling (use drill bits with 122 degree tips).
For the drive rod, any 1/4-20 all-thread or
a very long 1/4-20 bolt will do; accuracy of the bolt is not a factor because
the error inherent in the mount and drive will exceed any error in the bolt.
For the camera, I wonder why you want to
start out with a 6x7 size? THe Pentax is a superb camera but it's VERY heavy and
will be that much harder to move smoothly with your mount. A 35 mm camera will
do a nice job and most are much lighter (and cheaper) than the Pentax. If
you do go with the Pentax, I would recommend loupe, placed directly on the
focussing screen and focussed on the fresnel lines on the screen as a focussing
aid. Use at least 8x power and it should do the job.
Tripod and heads: the Manfrotto should do
the job; not sure about your specific model. Use the geared head so that you
have 3 dimensions of movement. Remember that you will want the barndoor
mounted directly on the head so that you can polar align it. You can use the
fluid head (or a simple ball head) to couple the camera to the barndoor and
permit easy pointing at the area of sky of interest.
Positioning the camera on the mount: See
the pointers in Dickinson & Dyer's Backyard Astronomer's Guide or check out
the internet articles on construction. Doubt if it's much of an
issue....
Hope this helps...
Bert
|