From: "Milton Aupperle" <milton@outcastsoft.com>
Date: February 13, 2008 12:52:11 PM MST
To: Astro_IIDC@yahoogroups.com
Subject: Off Axis Guider Rig
Hi Folks;
I posted two images to the "Other" files folder.
The first:
http://groups.yahoo.com/group/Astro_IIDC/files/Other/OAGSetUpParts.jpg
shows what my Celestron Off Axis Guider (OAG) set up looks like and
the labeled parts for it. I have a tendency to forget how it was
assembled and that bit me big time on the one good clear night of
seeing we had over x-mas from a dark site. I got no images because I
could not get the two cameras in focus at the same time and with this
image and parts list, that won't happen again. Trying to get 2 cameras
para focal at -25°C with a wind chill to -40°C is not really how I
wanted to spend new years eve.
The pick off prism on the OAG can be tilt adjusted which give me a
"donut" field of view that is between 18 to 39 minutes or arc in
radius from the image target. That give a good range for finding a
suitable guide star, which is typically in the Mag 6 to 9 range.
One of the nice things about this setup is that the 2" Filter ring
holder is behind the Off Axis Guider, which means the guide Camera has
no light lost for the LPR or IR filters I use. And if I decide to
switch to an R G B filter wheel with imaging camera, the Guider will
still be in front of it, so no light lost due to filters.
And lastly here is a "live action" snap shot of what it looks like in
practice taken February 8, 2008 :
http://groups.yahoo.com/group/Astro_IIDC/files/Other/TrackingM46FullScreen.jpg
Turbulence was horrible that night with the Mag 5 guide star jumping
+/- 3 pixels all over the place. We had wind gusts to 50 kmph which
didn't help either, but it always recovered when it got "hit" with a
gust. And with M46 only 20 degrees above the horizon I was shooting
though some pretty murky light polluted skies too.
Hope that helps someone..
Milton Aupperle