×

INDI Library v1.7.9 Released (23 Jun 2019)

INDI Library v1.7.9 is mostly a maintenance release to fix a few bugs in several drivers.

polar alignment moved????

Replied by knro on topic polar alignment moved????

Andrew, that's great! Thanks for the confirmation!
Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info
2 months 2 days ago #38262

Please Log in or Create an account to join the conversation.

  • Posts: 93
  • Thank you received: 17

Replied by fmozza on topic polar alignment moved????

I see a variance of around an arc minute or so between polar alignment measurements. Back-of-the-envelope calculations suggest that the variance is within the errors of mid-range mounts. (I'm using a CEM60 and it works very well for the loads I put on it.) It's not going to be perfect, and we shouldn't be obsessed with these measurements. With a 120mm refractor f7.5 imaging scope and an 80mm f4 guide scope, I've achieved 35" RMS on my CEM60 which is better than I expected. I can't get quite as good with a C11 + the same guidescope on the mount, but mount dynamics are quite a bit different for the C11 load - PHD2 reports I'm between 0.5 and 0.8 arcseconds RMS with the C11 which is pretty good.

Recent guidance from the PHD2 folks suggest you should not strive for a perfect polar mount as that can contribute to oscillation in DEC, and instead, a bit of polar misalignment helps to steady DEC . The amount of misalignment depends on the length of sub-exposure and plate scale which determines the amount of rotation you will see in the image. PHD2 tends to settle down at a couple of arcminutes off NCP, but that is likely because I polar align the image axis, not the guide scope which is not perfectly aligned with the image scope.

Bottom line is the EKOS polar alignment works very well,

PHD2 Best Practices is an excellent read, and work really well with EKOS/INDI.

jmh
The following user(s) said Thank You: pentaxian23
Last edit: 2 months 2 days ago by fmozza.
2 months 2 days ago #38271

Please Log in or Create an account to join the conversation.

  • Posts: 422
  • Karma: 3
  • Thank you received: 61

Replied by pentaxian23 on topic polar alignment moved????

fmozza wrote: I see a variance of around an arc minute or so between polar alignment measurements. Back-of-the-envelope calculations suggest that the variance is within the errors of mid-range mounts. (I'm using a CEM60 and it works very well for the loads I put on it.) It's not going to be perfect, and we shouldn't be obsessed with these measurements. With a 120mm refractor f7.5 imaging scope and an 80mm f4 guide scope, I've achieved 35" RMS on my CEM60 which is better than I expected. I can't get quite as good with a C11 + the same guidescope on the mount, but mount dynamics are quite a bit different for the C11 load - PHD2 reports I'm between 0.5 and 0.8 arcseconds RMS with the C11 which is pretty good.

Recent guidance from the PHD2 folks suggest you should not strive for a perfect polar mount as that can contribute to oscillation in DEC, and instead, a bit of polar misalignment helps to steady DEC . The amount of misalignment depends on the length of sub-exposure and plate scale which determines the amount of rotation you will see in the image. PHD2 tends to settle down at a couple of arcminutes off NCP, but that is likely because I polar align the image axis, not the guide scope which is not perfectly aligned with the image scope.

Bottom line is the EKOS polar alignment works very well,

PHD2 Best Practices is an excellent read, and work really well with EKOS/INDI.

jmh


Interesting. I noticed Trevor on AstroBackyard gets pretty good guiding but he only does polar alignment with a polar scope, so he would probably have a couple of arcmins of error. Maybe the guide scope PA can be avoided on mobile setups.
2 months 1 day ago #38294

Please Log in or Create an account to join the conversation.

  • Posts: 1578
  • Karma: 5
  • Thank you received: 134

Replied by Gonzothegreat on topic polar alignment moved????

So in a nutshell, if you are guiding you do not need A perfect alignment, but if you're not guiding you actually do need near perfect to be able to do long exposures.
I was able to reach 5 min un-guided the other day without any apparent star trails. And After I got the guiding on "track", 10 min exposure.
Kstars Mac osx
Odroid C1 running indiserver (kept up-to-date with apt-get update/upgrade)
HEQ5 pro / QHY5 / Atik 314L+
2 months 1 day ago #38295

Please Log in or Create an account to join the conversation.

  • Posts: 422
  • Karma: 3
  • Thank you received: 61

Replied by pentaxian23 on topic polar alignment moved????

Gonzothegreat wrote: So in a nutshell, if you are guiding you do not need A perfect alignment, but if you're not guiding you actually do need near perfect to be able to do long exposures.
I was able to reach 5 min un-guided the other day without any apparent star trails. And After I got the guiding on "track", 10 min exposure.


Good point, and it reminds me I should be more careful in what I way. Slightly off PA may help guiding but the longer the exposure, the more important the PA is. Even with good guiding, longer exposures will result in image rotation about the guide star if the PA is not very good.
2 months 1 day ago #38296

Please Log in or Create an account to join the conversation.

  • Posts: 1578
  • Karma: 5
  • Thank you received: 134

Replied by Gonzothegreat on topic polar alignment moved????

When I say "you do not need A perfect alignment", I do not mean by that a rubbish PA. It has to be as good as it gets without loosing sleep over it sorts of speak ;)...
Kstars Mac osx
Odroid C1 running indiserver (kept up-to-date with apt-get update/upgrade)
HEQ5 pro / QHY5 / Atik 314L+
2 months 1 day ago #38297

Please Log in or Create an account to join the conversation.

  • Posts: 93
  • Thank you received: 17

Replied by fmozza on topic polar alignment moved????

Gonzothegreat wrote: When I say "you do not need A perfect alignment", I do not mean by that a rubbish PA. It has to be as good as it gets without loosing sleep over it sorts of speak ;)...


Yes. You want to be reasonably close. The attached chart is the best results I've had with PHD2 on my CEM60 and I was about an arcminute off. Looking at the scatter plot, you can see that RA was worse than DEC (but still very good at 0.31").

There are websites that will compute the amount of rotation you will get for a given alignment and image plate scale, so you can get an estimate of how close you need to be for a given exposure length.

Regards,

jmh
The following user(s) said Thank You: Gonzothegreat, pentaxian23, wvreeven
Last edit: 2 months 1 day ago by fmozza.
2 months 1 day ago #38317
Attachments:

Please Log in or Create an account to join the conversation.

  • Posts: 842
  • Karma: 6
  • Thank you received: 223

Replied by wvreeven on topic polar alignment moved????

Now the big question of course is: what RMS does Gonzo get now his polar alignment error increased from 12” to over 1’?
ASI1600MM-Pro Cooled and filter wheel with a SkyWatcher Esprit 80 ED on a SkyWatcher HEQ5-Pro

ASI1600MM-Pro Cooled and filter wheel with an 8" TS Ritchey-Chrétien on a SkyWatcher EQ6-R
2 months 1 day ago #38322

Please Log in or Create an account to join the conversation.

  • Posts: 1578
  • Karma: 5
  • Thank you received: 134

Replied by Gonzothegreat on topic polar alignment moved????

Not sure when the next clear night will be, not looking good at the moment.
Tempted to really get this PHD2 working for me.
Kstars Mac osx
Odroid C1 running indiserver (kept up-to-date with apt-get update/upgrade)
HEQ5 pro / QHY5 / Atik 314L+
2 months 1 day ago #38327

Please Log in or Create an account to join the conversation.

Time to create page: 0.701 seconds