dhickey

I was researching something else when this thread showed up in Google. I don't know if you have since solved the issue, but I had something very similar with my AT115EDT that I recently resolved. In my case, the equipment is the AT115EDT, MoonLite focuser, ASI294MM with 1.25" AstroDon filters, the AT2FF field flattener (I have the reducer too but haven't used it in a while), and a Pegasus Falcon rotator. I saw the exact same ring as in your original post. Long story short, after meticulously checking each part of the imaging train the culprit was the focuser. Specifically, the adapter that threads into the 68mm drawtube on the MoonLite and adapts it down to 42mm threads. It's a flat black surface, but applying flocking material from ScopeStuff eliminated the large ring in the images. When I looked down the imaging train with the camera removed, I didn't initially see any reflections, but if I moved my eye slightly off-center, I could see it. The flocking on that adapter eliminated it both visually looking in from where the camera is as well as in the images. It was only present in the LRGB frames, the narrowband were fine. I'm guessing because I'm under very light polluted skies (Bortle 7/8). Along similar lines, I had an earlier issue where I saw arcs in the corners, so it looked like a very large reflection that was clipping the edge of the sensor. That one turned out to be the filters. AstroDon 1.25" filters, and again, the inside of the mounting ring was black but looked a little shiny on the LRGB ones. I cut a thin piece of flocking material and carefully applied to the inside of the mounting ring. The next time I imaged, those artifacts in the corners were gone. Dave

Agree, I don't think it's backlash as that should present at the peak when the direction is changed from north to south. Pulse guiding. Calibrating and using the GA near the equator/meridian (as close as I can due to tree obstructions anyway). It seems most likely it is stiction. I opened the mount up over the weekend and the Dec worm-end was way too tight, which has been corrected. No ground up bugs, metal shavings, or other debris was seen. The grease had very thick globs on one side of the Dec worm. There was some dried grease on the RA bearings. After reassembly and testing I still see the problem show up. The interesting part is that guiding works very well (~0.5" rms), plate solves work fine, etc. I tried swapping to a lighter OTA (70mm SV70T) and saw the problem there as well, so it doesn't seem to be related to weight. Dave

Michael, I will do that, thanks. Dave

I have an Atlas Pro mount that is 4 years old, the last two of which it has lived on a pier in the backyard covered by a Telegizmos 365 cover. Last week I put my AT130EDT back onto it and started seeing some odd declination behavior. See the attached screenshot from the PHD2 Guiding Assistant. Has anyone seen (and solved) this problem before? I saw a thread on Cloudy Nights that was inconclusive about a similar issue and most of the responses centered around backlash. The Dec backlash has been adjusted and is fairly small (~150ms) and as the graph shows, the south motion goes along fine until it suddenly doesn't, which does not seem to indicate backlash as a cause. I have checked the Dec balance and tried both perfectly balanced and slightly out of balance with very similar results each time. The attached graph was done with the scope pointed nearly at the zenith although I have tried other orientations as well. I had one run where it moved fine all the way to completion, but the next looked similar to this. I haven't been able to correlate it to anything reliably yet. The AT130EDT with the filter wheel, OAG, and camera comes in at 26lbs. Although that's 59% of the advertised 44lb capacity, I have not seen this behavior in the past two years of using this scope and mount. For power, it is being driven by a Powerwerx AC/DC supply at 14.1v, which is what I've used also for about two years. Slews are fine, everything sounds fine. I tried a short imaging run to see how it would manifest itself and after a few dithers the Dec will go off into never-neverland and take several minutes to be brought back. I took the side panel off to take a look at the belts to make sure they weren't loose or dry-rotting - the tension on both RA and Dec felt good and they appeared to be in good condition. Since the weather has halted any further troubleshooting for the next several days... any ideas? Thanks, Dave