guiding question

[rikyuu]

I should soon have a Meade DSI to play with to start taking some longer exposure images. Having not done accurate polar aligment as yet, that will be my first thing to practice and I hope to use WCS to help with that.

Then, continuing along this slippery road to financial ruin , I expect to become interested in guiding and so here come the questions!!

From my small understanding of guiding using a guide scope, I believe the idea is to use it to make small corrections to the RA and DEC positions when the guide star drifts. Am I correct in thinking then, that the guide star has to be viewed at a higher magnification than the imaging scope so that any drift is apparent in the guide scope, long before the image is affected?

If this is correct, and the imaging camera and guiding camera have similar size CCDs, then I presume that the guiding scope would have to be a much longer focal length, or use a 3x barlow for greater magnificaiton. Do people get away with using small refractor guide scopes on a long focal length SCT because the imaging camera has a large CCD, hence relatively wide FOV compared to the guide camera?

Thanks!

[Psychobilly]

In the past and for manual guiding your assumptions are correct ...for modern autoguiding systems the software calculates the centroid of the star to a fraction of a pixel so you can get away with using a shorter focal length guide scope...

Billy..

[blinky]

I have guided my 1.2m focal length Newt with a ZS66 @ 550mm (I think) and it worked a treat!

[barkis]

Yep!, times have surely changed. I used to guide at 3x the focal length of the imaging scope. What a pain.

It was a real challenge, which was why my Lunar to DSO ratio was about 200:1. :laughing2:

Ron.

[Psychobilly]

I still like to guide my Reduced STR with the 8" as I am too lazy to properly drift align....but did guide the 8" at F10 with the STR the other night

Billy...

[beamish]

I have guided my 1.2m focal length Newt with a ZS66 @ 550mm (I think) and it worked a treat!

Snap ! ( on those rare cloudless occasions)

[rikyuu]

Thanks all, glad I got the first bit right. Manual guiding does sound a bit of a pain although a few minutes wouldn't be too bad. I would have to use the 10" Newt as a guide scope (bit of an overkill) and get a short focus refractor for imaging.....which moves me nicely on to autoguiding!

I think I have the basics for this, but my mount is a simple EQ6 and my guide camera would be the Mintron video camera (via a USB capture device to the laptop).

Is there a nice bit of (preferably free or cheap) autoguiding software, that would take the input from a guiding video camera via USB and output RA and DEC adjustments via the parallel port? I can easily make up an adapter for the parallel port pins, to control the RA and DEC buttons on the EQ6 handset via some optoisolators. Would the 2x speed of the EQ6 be slow enough for the adjustments required?

....think I've found the answer with "guidedog". Looks promising....now to modifiy the hand controller.

Thanks again