How many times before I start imaging, should I run the polar alignment? I usually do once. I try to get it under 1'. I will then notice my guiding is off, so I will move my mount to the home position, run the 3PPA again, only to see it is off.
Why the discrepancy between alignments? Do I need to run it multiple times? Sorry for the beginner question.
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For me, it is important that the alignment from the home position is well below 0.4. If the setting takes longer, I go back to Home and start again. So it can happen that I start it 3-5 times until it fits.
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Hi Keith, Assuming you are using your primary imaging camera to perform the polar alignment, I would recommend to repeat the procedure at least 2 times. I found out that in my case that holds true and Guiding is much better. Sometimes, I even end up with 3 attempts if I am not happy with consistency. The difference in polar alignment error may come from flexure in your setup (not sure what exactly might cause it) Also I have to note here, that there is no such thing as perfect polar alignment. Even when nina reports that I am aligned with error  0 arcsec, I take this number with a grain of salt. Next time, try to repeat 3PPA two times for better consistency and see if that helps your Guiding.
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I am no expert on this topic, but have been using the NINA 3 point alignment now for a while. I too, find that I have to do it at least 2 or 3 times before I get it correct. At some point if I let it run too long, it gives me a message that it recommends that I start over. The more I use it, the better I get at figuring out how it is supposed to work. I am finding it much better than the polar scopes that I had been using. It takes longer, but the PA seems much better. Good luck and clear skies!
Mark
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I think you are confusing the Polar alignment and target tracking using PHD2. Usually you should align your mount to the Polaris star every several months.
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Once, unless the message pops up in the tppa routine that says i started a long ways away from the pole. If that happens, I get get it sorta close before restarting and doing a second run.
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Perhaps the post above is assuming the mount is on a pier, not a tripod. My tripod is often on grass and may settle into the ground over several minutes after placement. After setup I check it again before beginning an imaging session. About half the time it has moved enough to be corrected. If the session is a long one (2+ hours), I may check it again if guiding has slowly worsened. This is almost never a problem on concrete.
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I would recommend using sharpcap for polar alignment.
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D. Jung:
I would recommend using sharpcap for polar alignment. *** I used it too. It costs 15 pounds a year. But I think PHD2 allows to align Polar too. So I will not renew my SharpCap account this year.***
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I use PHD2 guiding assistant to “grade” my polar alignment. If PHD2 guiding assistant shows a polar alignment within 5 arcminutes, I get fine performance. I am really happy if it is less than 2 arcminutes. If it over 5 arcminutes I’ll re-accomplish the TPPA
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I use PHD2 guiding assistant to “grade” my polar alignment. If PHD2 guiding assistant shows a polar alignment within 5 arcminutes, I get fine performance. I am really happy if it is less than 2 arcminutes. If it over 5 arcminutes I’ll re-accomplish the TPPA *** Through SharpCap I get 10 arc sec aprox.***
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Kai Linde:
For me, it is important that the alignment from the home position is well below 0.4. If the setting takes longer, I go back to Home and start again. So it can happen that I start it 3-5 times until it fits. Ditto, I definitely try to get the initial total error to be .4 ~ .3 arc sec or better. Then I immediately repeat the polar to confirm that the new value is close (expect some variation). If you are starting off with 1 sec total error, you are likely going to have guiding issues - I mean PhD total error in the .7+ sec total error range. With a good initial polar alignment you should be able to get the PhD total error down below .7 arc sec. If you are seeing your polar alignment get worse after a short time, I would check tripod leg tightness, balance (critical) and levelness. Try lowering the tripod height as well. My experience with PA changing during a session has pointed to mount stability issues as the likely cause.
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You shouldn't have to repeat your PA at all if it's within a few arc/min your guiding should be fine. If you are finding that PA is changing then you likely have a lack of stability somewhere. Something could be flexing with changing orientation or your whole rig could be shifting if you have the sharp tripod points on soft ground. If that's the case, put a concrete paver under each leg. That should solve the problem nicely. Also keep in mind that often times, if you see a change in your guiding it's because of the seeing, not because the PA degrading. I use a fairly heavy EQ6R-Pro on its tripod. The rig sits on a brick paved area and is very stable. I do a PA about once a year.
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If you are guiding you do not need to be too precious about PA accuracy. Robin Glover did a detailed analysis that showed that less than 4 arcmins of PA accuracy is fine for guided work for a wide range of directions and exposures.
I’ve found NINA TPPA to work very well and tonight, when ipolar did a rare USB foul up, I ran TPPA once to a claimed error of about 30” and then proceeded to image Jupiter with Sharpcap using ROI tracking. I have been imaging for 90mins now and there is very little drift of the ROI across the sensor.
I think that people should look elsewhere for guiding error causes. Doing a good PHD2 calibration at low DEC is a good thing to make sure you have included. Soft ground can certainly be a problem and I’ve found scaffolding base plates very good. Basic balance is also important as it make sure all the nuts and bolts are tight.
I’ll repeat the first point: super accurate PA is neither necessarily nor sufficient for good guiding. One time I kicked my mount after PA and PHD2 said I was at 10’ error. I ran the session anyway and it guided fine, though the corrections on the PHD2 graphs were BIG, but errors remained low.
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I've used TPPA for four years now and have experienced similar problems. I usually end up redoing it 3-4 times but I haven't done a PA for a couple of years now. I upgraded from a guided rig on a tripod (Tak120, EQ6R) to a TEC140 on a 10Micron GM1000 mount, which has dual encoders, so I don't guide any longer. I've found that if I'm within 5-6', I'm good. Anything more and field rotation becomes an issue. Otherwise, I don't worry about it.
Paul
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I use the 3-point polar alignment plugin in NINA and if I am setting a scope up after moving the tripod I will run the alignment twice which consistently gets my setup to within 1-2 arcmin.
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Yo te recomiendo también SharpCap, es barato y muy rápido, sigue hasta que te lo califique "Excelent" o al menos "Good", son dos minutos y tendrás una alineación perfecta, similar a la precisión que se obtiene con Polemastar
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If you are experiencing a change in PA, you have some element not fixed or not stable, as already remarked by @George Tzellos and @Tony Gondola |
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Manu Oliva:
I use PHD2 guiding assistant to “grade” my polar alignment. If PHD2 guiding assistant shows a polar alignment within 5 arcminutes, I get fine performance. I am really happy if it is less than 2 arcminutes. If it over 5 arcminutes I’ll re-accomplish the TPPA
*** Through SharpCap I get 10 arc sec aprox.*** Does phd2 guiding assistant confirm this?
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SharpCap shows 10 arcsec when I align Polaris star. PHD2 shows a guiding error of less than 0.50 arcsec.
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I use a polemaster to get precise polar alignment of my mount. Takes minutes.
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Manu Oliva:
SharpCap shows 10 arcsec when I align Polaris star. PHD2 shows a guiding error of less than 0.50 arcsec. I think you misunderstand TiffsandAstro's question. When you run the guiding assistant in PHD2 it gives you your PA accuracy as part of the data analysis. That's the number he's asking about, not your average RMS guide error.
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Manu Oliva:
This is a hacked obsolete ZWO ASI 034MC camera used as Polamaster in a G11 Losmandy mount. It is used to align this mount to the Polaris star through SharpCap app. That's pretty genius. Well played.
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For me it depends on the mount, where I'm located and the OTA that sits on it. I have two permanent piers in Phoenix (PierTech PT2 with a NYX-101 Mount and a PT3 with an AP1600AE) and one in Overgaard (Planewave L-350). On permanent piers I tend to do a PA about once a month. I can usually tell when it is time as I always start my NINA sessions with a point to a low target in the east just to check focus, pointing accuracy and guiding. On both mounts I like to use a pole master camera and sharpcap as that always tends to give me a faster and more accurate PA. I look to get my total PA error under 1' and I call it good. When the initial pointing error starts to get close to 30' I take note and then redo my PA. Trying to judge PA error from guiding alone is difficult because there are many other factors involved such as local weather (wind), seeing, random clouds, airplanes, etc. Lots of things can affect guiding in addition to your setup and guide settings. On portable setups like my Redcat (on a AM5 with AA+ and carbon tripod), Vixen ED103S (NYX-101 on Berlebach Uni 18) or LX200 (EQ6R-Pro) I can usually let it stay for 2-3 days and then I have to redo it. These mounts I will use either ASI Air (Redcat) or NINA with the main camera (Vixen or LX200).
I have found that if my guiding is set up well, meaning I have good calibration for the setup, I've run Guiding Assistant and I have verified my guiding is well, I get good results with even a mediocre PA. Again the initial pointing error tends to be a better clue to me that my PA is about to be toast more than anything else. YMMV
Phil
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