dhickey

On 10/07/2023 at 00:05, jaydeepappas said:

Thank you to everyone who has replied so far. You all have given me a lot to think about and some new ways to approach this problem.

Since the issue doesn't show up when using narrowband filters I am currently shooting the crescent nebula, so that has been taking most of my time lately. It's nice to take a break from troubleshooting and actually start getting some more data again.

 

This is something I am considering, although I am skeptical since I received a new scope from the same company which had the same issue. Unless they are sending out all of these telescopes with incorrectly blackened focusers, which I doubt. But maybe my specific equipment has some weird interaction with this focuser in general. I am going to attempt more accessible troubleshooting steps before I resort to flocking the focuser interior.

I actually haven't tried this, but it is a quick and easy way to rule something out. I will give it a go!

This is perplexing to me. Since I have been shooting the crescent nebula, I haven't had any issues with artifacts using NB filters. I have no problems with calibration and my master lights turn out great. I have not changed any settings in WBPP since moving from LRGB to SHO. Is it possible to run a DBE or ABE on your resulting calibrated frame? I suspect that the ring is still there in your calibrated image but won't really show until a background extraction is done on it. At least this is what I've experienced so far.

This is some great advice, taking the images at different angles and using pixelmath to verify the movement of the focuser. Something I did not think of, and a pretty conclusive way to rule out focuser movement. When I received the scope I had to remove the CAA because the vignetting was moving around my images so much depending on the angle my imaging train was. After removing the CAA I could tell in my flat frames that the vignetting was still moving a bit, and tightening the focuser screws seemed to have fixed that. However I did not run any of the test flats through pixelmath - I was just verifying the movement in the flats with my eyes. Which is definitely not as accurate as pixelmath

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