Problem with TPPA in NINA

Timothy Prospero:
Hello, I see form the image that the stars are out of focus or have a lot of halos and gradient. this is not very good for Astap tp work. Can you retro to get better focus ? Youbcan alsonuse your main camera and main scope with TPPA, there isna reason why are you using the Guide scope?

Thanks a lot Timothy!

Yes I think that is out of focus, but yesterday i couldn't get a better focus, I'll try to improve that next time (today I hope).

I used the guide scope because I have planned to try the autoguide with PHD2, so I prepare the equipment for that. I'll try to do the TPPA with the main scope next time and then, if I am successful, move the camera to the guide scope to do the autoguide. Its better to do with the main scope? Sincerely, it makes more sense to do with that but i dont know if there are any reason more.

Clear skies!

Linwood Ferguson:
Assuming you plan to image with the main scope you should definitely polar align with the main scope, as the guide scope is never perfectly aligned with the main scope, and often can be quite far off.

I agree that it is better to use the main scope, it will have better resolution. However, where the guide scope is pointing shouldn't make a difference from a polar alignment perspective, since all you are doing is finding the center of rotation and aligning it with the celestial pole. The center of the circle will be the same regardless where the guide scope is pointing.

Linwood Ferguson:
Hmmm... I think you are right.  I had not thought that through completely, the plate solves are obviously off, but the rotation center is the same I think.  Had not considered that.

Yes - and indeed this is the reason why equatorial mounts work at all! It doesn't matter where you point in DEC, the center of rotation is always the NCP as along as you are polar aligned.

Linwood Ferguson:
Yeah, though where I get confused is that there is a field rotation that can get introduced guiding if the guide scope is unaligned

This deviates from the OP's problem, but it is still worth mentioning. The apparent rate of movement of stars in the sky is affected by atmospheric refraction and is hence slightly different depending on where in the sky your scope is pointing. That's why your guide scope and main scope have to point to the same place (or close). If they are markedly far apart, corrections will be inaccurate.

I should add that in order to have accurate & repeatable results using TPPA, you absolutely need to be in focus. I found that running a focus run before using TPPA makes the difference between having a good result, and having a garbage result. Poor focus can also affect ASTAP when doing a slew and center when using NINA. Because of this, I always do an initial slew to my target, followed by a focus run, and then a slew and center in order to really nail the target. Otherwise, I have found that I can be significantly off target which necessitates starting all over again and that is exactly what you don’t want to do when you are doing  any level of automated imaging.

CS,
Bruce

Alfredo Beltrán:
I also have the ASI462MC and, given its high sensitivity in the infrared, it needs a UV/IR (luminance) filter to achieve perfect focus.

I use an Astronomik L2 1.25” with this camera for guiding.

When I use the TPPA routine for aligning, I always use the main camera, through the main scope.

Thanks Alfredo for your advice. I'll keep in my mind for when i decide to improve my equipment.

Do you recommend that filter to do solar system photo too?

I would disagree that TPPA isn’t meant to be precise. I find it very precise giving you the ability to get your alignment error down to less than 10 arc seconds if you care to. I believe it also takes into account atmospheric refraction in order to be more precise. For the purposes of guided imaging, it’s unnecessary to be that precise, and depending on the equipment you’re using, having some amount of polar alignment error can actually help your guiding.  By causing your Dec corrections to be consistently from the same direction, a polar alignment error of an arc minute or so can help if you have backlash in the Dec axis of your mount. If on the other hand, you have a high precision mount with negligible backlash in the Dec axis, you can use TPPA to get the error down to where there is pretty much no drift in the Dec axis.

CS,
Bruce

Or talk to the author, pretty sure Stefan has said it.  

But there is really no such thing as completely accurate polar alignment.  I recall using TSX's "Accurate polar alignment" option, and at the end it would give you about 5 (vague memory how many) different options for your choice:  Refractive pole, actual pole, minimize DEC drift, minimize total drift, minimize rotation. There was a bit over an arc minute difference in these, and the presumption that each served a different purpose.

I've often asked when you should use refracted pole vs actual pole, for example (which is available in TPPA).  Someone told me "use refracted pole near the pole, use actual for the rest of the sky".  I do not know if that's correct guidance or not, but I am not at all sure the proper answer is to always correct for refraction. 

I used to have a screen shot of TSX's choices, but cannot find it.  Quite interesting for those in search of the one right answer.

Linwood Ferguson:

I would disagree that TPPA isn’t meant to be precise. I find it very precise giving you the ability to get your alignment error down to less than 10 arc seconds if you care to. I believe it also takes into account atmospheric refraction in order to be more precise. For the purposes of guided imaging, it’s unnecessary to be that precise, and depending on the equipment you’re using, having some amount of polar alignment error can actually help your guiding.  By causing your Dec corrections to be consistently from the same direction, a polar alignment error of an arc minute or so can help if you have backlash in the Dec axis of your mount. If on the other hand, you have a high precision mount with negligible backlash in the Dec axis, you can use TPPA to get the error down to where there is pretty much no drift in the Dec axis.

CS,
Bruce

Or talk to the author, pretty sure Stefan has said it.  

But there is really no such thing as completely accurate polar alignment.  I recall using TSX's "Accurate polar alignment" option, and at the end it would give you about 5 (vague memory how many) different options for your choice:  Refractive pole, actual pole, minimize DEC drift, minimize total drift, minimize rotation. There was a bit over an arc minute difference in these, and the presumption that each served a different purpose.

I've often asked when you should use refracted pole vs actual pole, for example (which is available in TPPA).  Someone told me "use refracted pole near the pole, use actual for the rest of the sky".  I do not know if that's correct guidance or not, but I am not at all sure the proper answer is to always correct for refraction. 

I used to have a screen shot of TSX's choices, but cannot find it.  Quite interesting for those in search of the one right answer.

I agree with everything that you've said. I'm an MX+ owner, & I rarely do a T-Point model at this point, finding for myself that I have excellent results with PEC enabled & a good polar alignment. I realize that there are a number of accepted different options/methods for judging the accuracy of polar alignment. This is beyond the scope of relating a basic understanding of using available tools to get an appropriate/adequate polar alignment for a given equipment setup. I can say though that if I run TPPA, and adjust it so that there's about a 1 arc minute error, I will have dec drift in a particular direction if I turn off my guiding. If  I run TPPA, and adjust it down to a total of close to 10 arc seconds total error, & turn off my guiding, I have no discernible dec drift over a few minutes time. Practically speaking, to me that's what a perfect polar alignment means. Since my MX+ has very little dec backlash, that's what I often go with. If I'm using my Atlas Pro mount, having some drift is best, so I shoot for an arc minute of error when polar aligning & that works well for that setup.

CS,
Bruce

I agree with others on focus, use primary scope.  But also would like to add that you need to make sure your focal length is correct.  Been there, done the wrong focal length.

Indeed, I would say plate solving failures reported on NINA's discord mostly come to either improper setup of ASTAP (wrong or no database) or wrong focal length. This can be especially true in a few cases: 

• People with barlow or reducers: You must put in the total, final, net effective focal length considering all modifiers
• Camera lenses often are labeled a specific focal length but in fact at infinity are something quite different
• A related issue is people using the "crop" focal length, they will read some idiotic manufacturer quoting "35mm equivalent" or such and use that -- you want the real optical focal length.


• Zoom camera lenses - you have to change focal length if you change the zoom, each time, every time.

One thing people can do is take a good clear image with lots of stars and save it, and run ASTAP manually, hit the sigma button and go to the pixel math 2 tab and it shows the effective focal length. You should use that in NINA, it is "right" even if you think it is not what it should be.

This is really true for all non-blind plate solvers not just ASTAP (and  you do not want a blind solver really for NINA, since they take a long time). 

Also, ASTAP changes somewhat rapidly, and it is a good idea to keep it at least fairly current: https://www.hnsky.org/astap.htm

Hello everyone!
Yesterday I made my first attempt at polar alignment with the Three Point Polar Alignment plugin using my NEQ 3-2 mount with motors (no go-to) and the ZWO462MC PRO camera with the ZWO 30/120 guide tube. With this equipment I had to use the manual method.

I had previously configured the ASTAP application with the D50 catalogue, but during the process I had problems solving both the first 3 recognition images and the images it takes in a loop showing my alignment error. The problem is that not always ASTAP can solve the photo, trying it in a loop until I move a bit more de AR axis.

This problem increases the time it takes to get the first three detection images, but I manage to get them by moving the AR axis a little more after several attempts. However, in the error correction phase this problem makes it impossible for me to correct this error as I have to move the sleeves around to get the image and this changes the error.

I am including a screenshot in case anyone sees an error, and so you can judge the quality of the photo. I always try to show more than 30 stars with photos of about 10 seconds exposure. This test was taken from my balcony and there is a lot of light pollution, so maybe that is the problem...



I can give you any other information you need.

Thank you very very much!

Hey!

Ahmad here, and I totally feel your frustrations with polar alignment. I've dabbled with similar setups in the past and faced some similar challenges. The ZWO462MC PRO is a solid camera, and the NEQ 3-2 is a robust mount. However, polar alignment can be a tricky process, especially in light-polluted areas.

Based on your description, a few things come to mind:

Light Pollution: This can be a significant factor when you're trying to get a clear image for alignment. Even with a 10-second exposure, the light pollution might be washing out some of the fainter stars that ASTAP needs to solve the image.

Image Clarity: It might be worth checking if the images you're capturing are clear and not blurred due to any focus or movement issues. A blurred or slightly out-of-focus image might give ASTAP a hard time solving.

ASTAP Settings: Ensure you've set the correct parameters in ASTAP for your equipment and observing conditions. A misconfigured parameter might result in failed image solving.

Star Saturation: Overexposing the brighter stars might create issues. Try to ensure that the stars aren't overexposed in your images.

Mount Movement: Any movement, even slight, can affect the alignment process. Ensure the mount is stable, and there's no play or backlash causing the movement.

Looking at a screenshot would definitely help, but I'm afraid I can't directly view images through this platform. However, I'd suggest comparing your images to solved ones available online or in ASTAP forums to gauge if there's a significant difference in quality.

Polar alignment can indeed be a time-consuming process initially, but with practice, it gets more manageable. I hope you find these suggestions helpful, and wishing you clear skies ahead!