advice on autoguiding

Hi

After having limited success with an unguided CGE mount I now want to try and upgrade to autoguiding. To help with this I have ordered a WO Megrez 72 from Ian King and a mini dovetail/ guide rings from ADM to use as a guidescope and widefield imager with my Canon 450D.
What is the a good autoguider system? I have a DFK 21 camera. Can I use this with one of the free autoguiding software packages available? Will I need one of the GPUSB adapters? Please excuse the dumb question but I have no idea about autoguiding.

John

John - I have very limited knowledge of autoguiding - I don't do it myself. But having seen many articles/posts etc the main gotchas seem to be:

1. Flexure - your guidescope needs to be very firmly attached the main scope (not sure what your main OTA is). Bear in mind that what you *think* is firmly mounted may not be so...
2. Image scale (arcsec per pixel) - the guidescope and imager need to be "matched" - not sure what the rule of thumb is for guiding. For the main scope, two times your typical FWHM is the general guide. I might be wrong, but that more than likely applies to the guidescope too.
3. Cabling will be an issue especially with a GEM - make sure all cables can clear the mount especially if you'll be leaving the scope unattended. Tie-wraps are usually good enough.
4. Guide Software settings - assuming all other issues are sorted and the software is correct for your system, I think the next issue is how aggressively the software controls or corrects the mount.

As I said, I have limited knowledge. Others here will be able to chime in with far more detail than I but the items above should give you a guide as to where your research should be directed. Perhaps goggling "autoguiding" might help...

Cheers and HTH

Dave

Hi John,

On top of what Dave said I'd add a couple of things.

As the DFK 21 does not have a dedicated autoguiding output you will need some way of getting the guiding commands from your autoguiding software of choice to the mount. You basically have two options.

1. GPUSB - This will do the job just fine.
2. The standard CGE serial (RS232) cable. You can autoguide through this too using the ASCOM driver)

GPUSB has the advantage of that commands are acted on more quickly.

I suggest using PHD Guiding as its free and easy to use. Once you have the scope and camera connected (via your cable of choice) it really is just a matter of clicking the start button. PHD goes off and figures out all the calibration stuff and then begins autoguiding immediately. It's usually pretty foolproof. You can tinker with some of the agressiveness settings later to tweak the guiding. As a general piece of advice keep the axes of your guiding CCD more or less lined up with the RA and DEC axes of your scope. This means less calculations for your guiding software and also guiding corrections are often in one axis only rather than two at the same time.

I use a QHY5 guider as it provides a dedicated autoguider output avoiding the need for stuff like GPUSB or the RS232 cable for guiding at all. (standard ST4 type guiding cable just goes straight from camera to mount)

As DaveMc said, do not underestimate the flexure issue, be careful of having too many fittings between the guidescope and camera. e.g. a star diagonol is not a good idea. Use a solid straight-through adaptor if you must to reach focus.

Thanks Guys.
Has anyone succcessfully used a DFK camera for autoguiding before. I couldn't find anything on the forums.