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I've been having what is becoming a frustrating experience with large RA spikes. I've lost track of how many nights that I've focused on just getting guiding under control, maybe 5 or so. I've switched my setup from my APO to my SCT for galaxy season, so there's a bunch of recent changes, but all of the equipment was used before and performed pretty well. This exact setup has performed performed around 1.1 to 0.7 RMS, and this was before multistar-phd2. Right now I'm having a hard time keeping it below 2.0 RMS. There are some huge spikes (10 .. 14 or so) happening somewhat regularly, but not on a precisely regular schedule. Here's some examples of the time gaps between the spikes: 197s, 247,? 412, 485. The setup is an EdgeHD8 with a 0.7 focal reducer and an OAG. 178MC camera for guiding. I'm thinking of switching to the guide scope just to see what I can find. If everything is great there, then maybe there's some sort of flexure in the OAG image train.? I've gone through things carefully, making sure my PA is good, balance is good, wires are not snagging etc. Help!!! This is not the infamous 76 second spike is it??? It's such a strange spike, maybe there's something going weird with the camera? I'm going to try and guide with the main camera just to see what I see.? Help!
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Dear Jamie,
Let's try to chase the cause...a couple of simple things to try:
1. Balance the mount in RA and DEC.
2. Now unbalance the RA: Wrap a rope or cord around the RA axis so the string drops to the East, and hang a weight on that.? Say 1 to 2 pounds should do it.
3. Try imaging and look for the same glitches.
If this remedies the glitch problem, the root cause is likely something in the RA drive... gear mesh gap.? There are several gaps that are built in.? The transfer gears have a gap (if you have a tucked motor system), and the worm to ring gear has a gap.? The hanging weight torque ensures the axis cannot shift during tracking and autoguilding.??
4. If this does not do the trick, please switch from your SCT to a refractor just to test if the cause is really the mount.? If the refractor imaging shows no glitches, it's possible one of the mirror holders in the SCT is loose.? Or the dovetail plate is not tight, etc.??
It's always hard to chase these glitches down.? Reflective optics are prone to loose optical elements.? ??
All the best,
Michael?
(I'm in Sunnyvale this week, not too far from you...if you want to get together, let me know).
[Edited Message Follows]
I've been having what is becoming a frustrating experience with large RA spikes. I've lost track of how many nights that I've focused on just getting guiding under control, maybe 5 or so. I've switched my setup from my APO to my SCT for galaxy season, so there's a bunch of recent changes, but all of the equipment was used before and performed pretty well. This exact setup has performed performed around 1.1 to 0.7 RMS, and this was before multistar-phd2. Right now I'm having a hard time keeping it below 2.0 RMS. There are some huge spikes (10 .. 14 or so) happening somewhat regularly, but not on a precisely regular schedule. Here's some examples of the time gaps between the spikes: 197s, 247,? 412, 485. The setup is an EdgeHD8 with a 0.7 focal reducer and an OAG. 178MC camera for guiding. I'm thinking of switching to the guide scope just to see what I can find. If everything is great there, then maybe there's some sort of flexure in the OAG image train.? I've gone through things carefully, making sure my PA is good, balance is good, wires are not snagging etc. Help!!!
This is not the infamous 76 second spike is it???
It's such a strange spike, maybe there's something going weird with the camera? I'm going to try and guide with the main camera just to see what I see.?
Help!
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Michael, you are awesome!?
So I've already switched my guiding to use the main camera, a ZWO ASI 1600MM Pro, from the guide camera, which is a 178MC. So far things are looking much better, but I'm going to give it some time to make sure that the spike does not show up. When I was looking at the star profile in PHD2 on the previous (bad) runs, I would see the star do a huge jump in one frame, and my gut feeling was that the camera somehow decided to deliver a bad image, the very next frame was back into a fairly normal position. I also have a ZWO 120MM USB2 version and it will occasionally give a half image, or an image that is positioned wrong in the frame. This somehow reminded me of this, but again, it's some detective work, and lot's of guessing going on. One thing of note is that it 100% happens in RA, not DEC, so my guess with the camera might be completely wrong...?
I'll let this play out for a while, and if I start to see the spikes again, I'll follow your advice.?
-- OK, so I'm still seeing some spikes showing up. They don't look as high, maybe 9 instead of 13, but that might just be some math with the focal length and pixel size going on in the PHD2 test profile that I made for the 1600. There is absolutely still a spike. I believe that this only happens with the scope hanging to the west, and weights to the east. I'll have to re-arange and try.?
We should absolutely get together sometime soon, regardless of this issue -- We're following some pretty strict covid rules though, so we keep to ourselves for now, but if things work out we may start loosening up in the next month or so.?
It's getting late, so I'll have to continue with this the next night.?
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OK, one more before I turn in. This is with the scope on the East side instead of the West. I'm not sure what to make of it really. It's pretty bad for one, keeping above 2 RMS. The huge spikes are gone, and replaced with some large jumping around all over. -- Not really sure what to think about this. I'll try some of your ideas next night.? Jamie
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Jamie
Screen captures aren't helpful for this kind of thing. if you can upload your guidelog that would be great
OK, one more before I turn in. This is with the scope on the East side instead of the West. I'm not sure what to make of it really. It's pretty bad for one, keeping above 2 RMS. The huge spikes are gone, and replaced with some large jumping around all over. -- Not really sure what to think about this. I'll try some of your ideas next night.?
Jamie
-- Brian?
Brian Valente portfolio
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I'll do that now. My plan for tonight is to switch to the guide camera where everything was working fine a couple weeks ago, before the recent rains.?
Jamie
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Here it is.?
I believe that from 19273 seconds onward the scope was on the East side, and before that point it was on the west.?
Jamie
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Jamie is your pixel scale really 0.34"?
the calibration looks really wonky too (or as a result)
Here it is.?
I believe that from 19273 seconds onward the scope was on the East side, and before that point it was on the west.?
Jamie
-- Brian?
Brian Valente portfolio
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Yes, using my 178 it should be 0.35 when using the OAG. I have binned it in the past but found that it didn't seem to help, so I just leave it native.?
Using my 1600 it should be 0.55 according to https://astronomy.tools/calculators/ccd_suitability, it should be 0.55 because of the 0.7 reducer.
?
I put in a focal length of 1471 in the PHD2 wizard. Which is not exactly the spec for the scope with the 0.7 reducer (1422). I did this because the solver complained that my calculated focal length was actually?1471, not?1422, so the image scale is slightly different than what astronomy.tools reports.?? I think that I calibrated a few times as I was trying things out, so there should be several in there. Jamie
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PHD recommended min limit for image scale is 0.5" so i would?bin 2 at a minimum
all of your calibrations are problematic?
here's a typical example
the calibration run should be 25 pix across 12 steps, which is shown in the outside circle of the target here:
you can see you have only one step in the circle
if i zoom way out i can see the rest of your calibration, which looks okay, but the step size is way too big
So i don't know what your settings are, but i recommend you bin 2 the guiding and start with a fresh equipment profile
this doesn't directly address your question, but i think having a solid foundation is an important first step here
Yes, using my 178 it should be 0.35 when using the 178. I have binned it in the past but found that it didn't seem to help, so I just leave it native.?
Using my 1600 it should be 0.55 according to , it should be 0.55 because of the 0.7 reducer.
?
I put in a focal length of 1471 in the PHD2 wizard. Which is not exactly the spec for the scope with the 0.7 reducer (1422). I did this because the solver complained that my calculated focal length was actually?1471, not?1422, so the image scale is slightly different than what astronomy.tools reports.??
I think that I calibrated a few times as I was trying things out, so there should be several in there.
Jamie
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-- Brian?
Brian Valente portfolio
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Thanks, you're right, I don't have very good calibration. I'll do that next time I'm out. But I don't think that it's related to the issue that I'm seeing. I generally use similar settings for the calibration, and I've had very reliable, and good guiding in the past. This spike is new, I don't think that I've ever seen it before. Tonight I'll be trying things out using the guide scope instead of the OAG. If the issue is still there, then I can eliminate possible issues with the SCT like mirror flop or some sort of looseness. If that fixes it, then there might be something going on with the SCT, or image train on the SCT.?
Jamie
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Yes, as I mentioned this doesn't directly address your bumps, but I think it's important to make sure everything else is working correctly
Another thing that would help is a longer unguided run like 30-45 min (guiding assistant or disable guide output)
If there's a problem in the mount, it will show there as well
might also doublecheck?PEC status and and TVC values
you have an SCT? ahhhh :)
Thanks, you're right, I don't have very good calibration. I'll do that next time I'm out. But I don't think that it's related to the issue that I'm seeing. I generally use similar settings for the calibration, and I've very reliable, and good guiding in the past. This spike is new, I don't think that I've ever seen it before. Tonight I'll be trying things out using the guide scope instead of the OAG. If the issue is still there, then I can eliminate possible issues with the SCT like mirror flop or some sort of looseness. If that fixes it, then there might be something going on with the SCT, or image train on the SCT.?
Jamie
-- Brian?
Brian Valente portfolio
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From the calibration graphs, it's not just the RA that has steps that are too large but the DEC calibration steps are almost all backlash clearance (the ones labeled B).? There are just a few small steps South, then North finally acts half way normal.
So, major DEC backlash problems during the calibration at least.? The large RA steps indicate there's something wrong in the settings, and PHD2 will therefore use a gain that's way off.? That could explain it.
Now, if I could only fix my own guiding problems...
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Henk
the backlash calibration looks fine to me? southern movement is not part of the calibration
you're right they are both too big
On Fri, Apr 2, 2021 at 12:53 PM Henk Aling < haling@...> wrote: From the calibration graphs, it's not just the RA that has steps that are too large but the DEC calibration steps are almost all backlash clearance (the ones labeled B).? There are just a few small steps South, then North finally acts half way normal.
So, major DEC backlash problems during the calibration at least.? The large RA steps indicate there's something wrong in the settings, and PHD2 will therefore use a gain that's way off.? That could explain it.
Now, if I could only fix my own guiding problems...
-- Brian?
Brian Valente portfolio
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Sorry
i should?have said
The DEC axis calibration?looks fine?
On Fri, Apr 2, 2021 at 12:57 PM Brian Valente via <bvalente= [email protected]> wrote: Henk
the backlash calibration looks fine to me? southern movement is not part of the calibration
you're right they are both too big
On Fri, Apr 2, 2021 at 12:53 PM Henk Aling < haling@...> wrote: From the calibration graphs, it's not just the RA that has steps that are too large but the DEC calibration steps are almost all backlash clearance (the ones labeled B).? There are just a few small steps South, then North finally acts half way normal.
So, major DEC backlash problems during the calibration at least.? The large RA steps indicate there's something wrong in the settings, and PHD2 will therefore use a gain that's way off.? That could explain it.
Now, if I could only fix my own guiding problems...
--
Brian?
Brian Valente portfolio
-- Brian?
Brian Valente portfolio
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I made a habit of making large steps for calibration sometime ago, and I honestly can't remember exactly why I did that... I think that PHD was complaining that my steps were too small, so I just increased them. I'll try and dial it in better tonight, but honestly I don't see how the calibration can account for the spikes, and that's my biggest issue.?
Jamie
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Hi Brian, that's not the same graph that you showed earlier.? Never mind though, I am just a disturbance trying to learn how to debug calibration problems.
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?hmmm
well the prior one i showed was pretty much the same, but maybe you didn't see the second image on that post
What calibration problems are you having?
On Fri, Apr 2, 2021 at 2:13 PM Henk Aling < haling@...> wrote: Hi Brian, that's not the same graph that you showed earlier.? Never mind though, I am just a disturbance trying to learn how to debug calibration problems.
-- Brian?
Brian Valente portfolio
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haha well i'll say it one more time?
"this doesn't directly address your question, but i think having a solid foundation is an important first step here"
Fixing symptoms with unknown?causes is always a process of elimination right? if we knew what it was, we'd just jump to the fix. But 99% of the effort is isolating the cause. So it makes sense to me that we want to make sure everything else is operating correctly, and eliminate one thing at a time
that's also why I mentioned the previous steps of doing an unguided run. if it shows up in the unguided results, we know it's the mount. if it's not we know it's not the mount, or at least not the mount by itself
i like your idea of testing without the SCT
I made a habit of making large steps for calibration sometime ago, and I honestly can't remember exactly why I did that... I think that PHD was complaining that my steps were too small, so I just increased them. I'll try and dial it in better tonight, but honestly I don't see how the calibration can account for the spikes, and that's my biggest issue.?
Jamie
-- Brian?
Brian Valente portfolio
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What calibration problems are you having?
I want to get to 0.5" RMS total but 1.2 is the closest I got, with the 12".? I'm looking at mechanical problems first.? The DIY spring loaded worms seem to work but I will check again, need to check the effect of tightening the clutches too.? I have equal errors in DEC and RA so it could just be poor seeing.? I will find out more tonight with the 6", just guiding no imaging.? Until it works.
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Jamie Amendolagine
Michael Herman