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Any ideas as to the cause of this pattern in the photo ?

Acquisition
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Michael Urvina avatar
Michael Urvina avatar

BlinkScreen.png

Autorun_Log_2026-07-10_223317.txt

PHD2_GuideLog_2026-07-10_222857.txt

Hello fellow astrophotographers,

I am hoping that one of you might know what is causing this unusual cross stitch pattern.

Over the past 2 nights, during the last hour or so of an autorun, I get some FIT files that look like this one. I had 47 perfect images in sequence, with sharp stars, then several of these shuffled throughout good frames. All of this happening during the last 25 or so shots during both nights.

The way the pattern is precisely repeated makes me think it’s probably mechanical, like a slipping belt or binding gear. However, I loosened the tension on both DEC and RA gears months ago. I followed the instruction of several well known astrophotographer YouTubers when doing this procedure to remove the stiffness in certain parts of the mounts rotation.

I do dither every photo and guiding over the last 2 nights was good with a RMS of .4 -.5 when last checked. Obviously something was off during the capture of the distorted photos but the problem was never present in any of the frames I took just two weeks ago.

Some things I’ve already checked or tried are :

-checked ASI AIR logs for any anomalies or errors like “lost star”

-updated all firmware

-recently replaced the motherboard in my EQ6r mount…dont get me started

-checked belt tightness on both drive motors

-recently inspected and or replaced wires and cables

-observed for any possibilities of snags while rotating

- mount rotation is smooth with and without a load

-because it’s fairly hot now, I’ve also been breaking everything down and taking it into the house after photographing so its not sitting outside in the heat.

I failed to find a comparable photo or like issue after searching many astrophotography sites. And because I don’t have enough experience to identify the issue based on what I see in the photo, I will ask for help or suggestions from the forum. I really don’t want to do a rebuild of the mount but I guess that may be necessary if I can’t find a root cause not mechanically related.

Thank you for your time.

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Brian Puhl avatar
Brian Puhl avatar

If you can, drop a guide log in here. I’m not so sure this is a mount issue, as the pattern is just too clean. It honestly looks like PHD was trying to calibrate, but you wouldn’t have seen a full box like that, only two legs. Certainly a weird one, but the oscillation is just too clean. I can’t put my finger on it. I’m not too familiar with how AsiAir operates in regards to guide logs, but it sounds like you were able to look at it.

📷 image.pngimage.png

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Michael Urvina avatar
Michael Urvina avatar

Brian Puhl · Jul 11, 2026, 11:26 PM

If you can, drop a guide log in here. I’m not so sure this is a mount issue, as the pattern is just too clean. It honestly looks like PHD was trying to calibrate, but you wouldn’t have seen a full box like that, only two legs. Certainly a weird one, but the oscillation is just too clean. I can’t put my finger on it. I’m not too familiar with how AsiAir operates in regards to guide logs, but it sounds like you were able to look at it.

Brian, thank you for responding.

I have added the PHD2 guide logs as well as the autorun logs. I wasn’t aware of the existence of the autorun logs at first but unless I’m missing something they also appear uneventful.

Maybe they will be of more use to you.

Thanks again

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Michael Urvina avatar
Michael Urvina avatar

Forgive the oversight but I now see that settling failed on some files after dithering. I hadn’t noticed that before. I’m assuming that would explain the pattern if the exposure resumed during a dither ?

I haven’t changed those setting in years but I guess the firmware update may have adjusted something. If not, what kinds of things could cause that type of failure ?

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Brian Puhl avatar
Brian Puhl avatar

Michael Urvina · Jul 12, 2026, 02:43 PM

Brian Puhl · Jul 11, 2026, 11:26 PM

If you can, drop a guide log in here. I’m not so sure this is a mount issue, as the pattern is just too clean. It honestly looks like PHD was trying to calibrate, but you wouldn’t have seen a full box like that, only two legs. Certainly a weird one, but the oscillation is just too clean. I can’t put my finger on it. I’m not too familiar with how AsiAir operates in regards to guide logs, but it sounds like you were able to look at it.

Brian, thank you for responding.

I have added the PHD2 guide logs as well as the autorun logs. I wasn’t aware of the existence of the autorun logs at first but unless I’m missing something they also appear uneventful.

Maybe they will be of more use to you.

Thanks again

Thanks! I glanced at the logs, and the events are easy to correlate. I can with a certain degree of confidence say this is not a mechanical issue. Both RA and DEC axes are repeating the same exact pattern. Since they are mechanically two different systems, we can rule that out. Also, they both diverge the same exact amount every time. Typically when you see divergences like this, it would be an external force like wind, or something bumping the mount. Again however, it’s just too perfect, exactly the same every time.

Glancing at the performance of your mount up until the problems happen, mechanically it looks fine. I think your backlash is adjusted properly and I don’t see any problems.

What does stand out however is all these problems occurred after a fresh calibration in PHD. It appears you have your mount set to recalibrate after flip. A bit unncessary in my opinion. Either way, none of these problems occurred until after flip and recalibrate. So we have two clues here: Recalibration and side of pier changes. Unfortunately both happened at the same time, so I can’t rule out one over the other.

I won’t lie, this is a good one. I’m not exactly sure whats going on. The excursions are 125 seconds each time, which is too fast to be a guide reaction or binding, cable drag. I think this is a glitch of sorts. I would start by resetting your PHD settings and starting fresh (again I don’t know how this works in an ASIAir). I believe you said you’ve probably already done this, as well as cables. Those two would be my first place to start.

Really thinking about it, I’m wondering if there’s something going on with your guide camera, maybe even the ASIAir itself. I think you’ll need to sit down with the mount one evening and try to reproduce this. If the fault continues, try running the system with a laptop, or a different ASIAir maybe. I’m going to show this to some friends and see if they have any feedback.

📷 image.pngimage.png

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Brian Puhl avatar
Brian Puhl avatar

Michael Urvina · Jul 12, 2026, 03:31 PM

Forgive the oversight but I now see that settling failed on some files after dithering. I hadn’t noticed that before. I’m assuming that would explain the pattern if the exposure resumed during a dither ?

I haven’t changed those setting in years but I guess the firmware update may have adjusted something. If not, what kinds of things could cause that type of failure ?

Guide logs suggest this is irrelevant to dither.

Michael Urvina avatar
Michael Urvina avatar

Brian Puhl · Jul 12, 2026, 03:37 PM

Thanks! I glanced at the logs, and the events are easy to correlate. I can with a certain degree of confidence say this is not a mechanical issue. Both RA and DEC axes are repeating the same exact pattern. Since they are mechanically two different systems, we can rule that out. Also, they both diverge the same exact amount every time. Typically when you see divergences like this, it would be an external force like wind, or something bumping the mount. Again however, it’s just too perfect, exactly the same every time.

Glancing at the performance of your mount up until the problems happen, mechanically it looks fine. I think your backlash is adjusted properly and I don’t see any problems.

What does stand out however is all these problems occurred after a fresh calibration in PHD. It appears you have your mount set to recalibrate after flip. A bit unncessary in my opinion. Either way, none of these problems occurred until after flip and recalibrate. So we have two clues here: Recalibration and side of pier changes. Unfortunately both happened at the same time, so I can’t rule out one over the other.

I won’t lie, this is a good one. I’m not exactly sure whats going on. The excursions are 125 seconds each time, which is too fast to be a guide reaction or binding, cable drag. I think this is a glitch of sorts. I would start by resetting your PHD settings and starting fresh (again I don’t know how this works in an ASIAir). I believe you said you’ve probably already done this, as well as cables. Those two would be my first place to start.

Really thinking about it, I’m wondering if there’s something going on with your guide camera, maybe even the ASIAir itself. I think you’ll need to sit down with the mount one evening and try to reproduce this. If the fault continues, try running the system with a laptop, or a different ASIAir maybe. I’m going to show this to some friends and see if they have any feedback.

📷 image.pngimage.png

Thank you so much for your willingness to use your time to help me with my problem.

Most of this stuff is above my paygrade so having someone with your knowledge is appreciated.

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Brian Puhl avatar
Brian Puhl avatar

Michael Urvina · Jul 12, 2026, 05:01 PM

Thank you so much for your willingness to use your time to help me with my problem.

Most of this stuff is above my paygrade so having someone with your knowledge is appreciated.

Please keep us posted! I’m very interested in the cause of this. I really think it’s a software glitch though.