Many thanks to both Bernd and Bill. Just after posting my last (!) I found the
part referred to in the link - and blushed appropriately ;-)

Bill - it is a Starlight Express guider as used in the AO unit. The guide
camera is offset a short distance from the main camera chip. The AO unit now
works a treat - after correcting the manual errors!!!

With a visual display of the frame in Guide, it would be so much easier. I'll
study Bernd's comments.

Lawrence

>Re: Second CCD frame?
> Posted by: "Bill J Gray" pluto@... feliks314159
> Date: Wed Mar 5, 2008 1:50 pm ((PST))
>
>Hi Lawrence,
>
> If you have a "standard", off-the-shelf camera such
>as an SBIG or MegaTek camera, you can just select your
>type of camera. Guide already "knows" where the guider
>chip is for these cameras, and will show it right away.
>(Fortunately, this handles things for about 99% of the
>world. Not many people are building their own cameras
>with guiding chips! Those who do usually have to follow
>the link Bernd mentioned, or just read the comments at
>the bottom of the "ccds.nam" file.)
>
> If you _do_ have a commercial camera that's not already
>in Guide's list, please let me know, and I'll add it.
>
>-- Bill