From: "Tim" <tjp314@pacbell.net>

Date: February 15, 2008 9:31:34 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: Off Axis Guider Rig

Milton:

I find these kinds of pictorials very helpful.  I don't have a

Celestron OAG, but I do have a Lumicon Easy Guider.  I don't like the

way it has to be locked down - with a tiny set screw bearing on the

threads on the back of the OTA, so I don't use it much.  I've tended

to prefer Guide scopes, but these can be tricky to mount securely

enough to eliminate flexure.

-Tim.

--- In Astro_IIDC@yahoogroups.com, "Milton Aupperle" <milton@...> wrote:

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