I just purchased a used STLX 11002 with self-guiding FW. I also purchased separately a new AO-X. The problem I am having is that with the AO-X attached, I am getting very elongated stars. When I remove the AO unit, I do not have this issue. Can any suggest a solution to this?
We'll need a lot more information to help you figure this out. First of all, does the elongation occur if the AO unit is not in operation? Can you provide a raw, unprocessed FITS image showing the problem?
Yes, the problem occurs when I am in focus mode. I am wondering whether the AO unit is running somehow even though I wasn’t guiding at the time. I will re-attach it and take some images when I am next out there. Thank you Doug!
Blinking is normal. If you want to be certain the AO unit isn't running... unplug it. If you still have an image problem then detach the AO and inspect its window.
I unplugged everything and exercised the AO unit. All appeared ok. I re-attached it and tried a focus image and I got the same elongated stars. I am uploading a 10 second image so can see what I get. It does not appear as bad on the west side of the mount but is still there.
This doesn't look like an AO problem. It looks like the mount is drifting rapidly in declination. (North appears to be at left in your image.) Over the course of a 10 second exposure, your stars are moving 11 pixels. Doing an all-sky solve came up with: All Sky Search Found Plate Center RA 04h 10m 55s, Dec 26° 31' 35" Focal Length 2915.3 mm, Scale 0.637 "/Pixel That 11 pixels at 0.637"/Pixel translates to about 7 arc-seconds. Sidereal rate is 15 arc-seconds per second. So it looks like it's drifting at 1/20th sidereal rate. That might be plausible if you're using a tracking interface cable that's wired backwards, because that tends to short out one of the N/S wires. If you are using a tracking interface cable, try unplugging it.
Brian, you have missed something really important. File... Settings... Site and Optics. You need to set up the Latitude/Longitude/Altitude of your site, and you need to put in the optical parameters. Keep in mind for the self-guiding filter wheel, it has a 0.7x focal reducer. Right now, they are all ZERO, so it won't guide or run the AO properly. FOCALLEN = 0.0000000000000000 /Focal length of telescope in mm APTDIA = 0.0000000000000000 /Aperture diameter of telescope in mm APTAREA = 0.0000000000000000 /Aperture area of telescope in mm^2 SITELAT = '00 00 00' / Latitude of the imaging location SITELONG = '00 00 00' / Longitude of the imaging location
Colin, Thanks for that information. I think I figured out the elongated star problem. Even after properly T-pointing, I was still getting the problem. It wasn't drift, I think the problem is that my backfocus is off. I had to order some new extenders because the ones that came with the RCOS 12.5" scope I bought do not have all of the extenders so I am off a bit when the AO unit is attached. I will play with again once I get the proper extenders and Precise parts is also making me an adapter for the camera. Thanks for all the input!
I finally figured out that the problem I was having was fan vibration! I tried turning off the fan and my stars were perfectly round! I am thinking of replacing the fan although I could not see, feel or hear anything wrong with it. I changed the fan setting from auto to 30% in the AO settings and this seems to work ok. Is there any harm in maintaining a 30% fan speed?
Wow, good catch. The fan vibration is probably at just the right frequency to excite some mechanical resonance in your telescope or mount. It should be fine with the lower fan speed, as long as you don't crank the cooler power to maximum. Just don't try to achieve the maximum possible delta-T.
