Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Aligning an AVX with a DSLR

  • Please log in to reply
13 replies to this topic

#1 proud clamper

proud clamper

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 26 Mar 2016
  • Loc: Reno, Nevada

Posted 24 April 2019 - 01:06 AM

Hello everyone.

I started into astroimaging several years ago but like many others I started too big, got frustrated and had to step back and take a sabbatical. I missed it terribly so I regrouped and 

I started up again, slowly this time. I obtained an iOptron Skyguider Pro and a WO ZS61 refractor with a WO field flattener and a Canon t3i fir imaging.  After about a year of practice and learning getting pretty good results I wanted to move up to something that would allow me longer exposures so I upgraded to an AVX mount and started using EOS Backyard. However I am a little confused, perplexed and downright nonplussed about the 2 star and ASPA. The posts I read all deal with using a polar scope and eyepiece. I am blessed with having a clear view of Polaris and since the Canon is live view I have been able to center Polaris in the crosshairs on the EOS Backyard program.  My question is, since the t3i is part of the imaging train, it should be seeing exactly what the Z61 is seeing correct? And if so, this would eliminate the need for a polar scope and/or eyepieces. I can just use the live view to do my star alignments. Am I missing something here?

Thanks in advance for all your help. 



#2 kyle528

kyle528

    Ranger 4

  • *****
  • Posts: 399
  • Joined: 02 Feb 2019
  • Loc: SE Ohio

Posted 24 April 2019 - 06:10 AM

Star alignments, yes, because it sees what the eyepiece would see. Polar alignment, no, because your polar scope MUST be aligned with right ascension in order to function as a polar scope. Now, using software for PA like sharpcap, you wouldn’t need the scope, but you need a camera it’s compatible with, I don’t believe dslr’s will work.


Sent from my iPhone using Tapatalk

Edited by kyle528, 24 April 2019 - 06:10 AM.

  • RedLionNJ likes this

#3 Jeff2011

Jeff2011

    Gemini

  • *****
  • Posts: 3494
  • Joined: 01 Jan 2013
  • Loc: Sugar Land, TX

Posted 24 April 2019 - 08:54 AM

ASPA (All Star Polar Alignment) is a built in hand controller polar alignment option that is done on a star away from Polaris.  If I remember they recommended a star near the meridian and celestial equator or something like that.  If you want to align on Polaris then use Polemaster.  SharpCap also has a great polar alignment tool. It won't work directly with your DSLR but you could use it with a guide camera or perhaps now their folder monitor option where it could pickup files from another capture program like Backyard EOS might work.



#4 the Elf

the Elf

    Surveyor 1

  • *****
  • Posts: 1595
  • Joined: 06 Sep 2017
  • Loc: Germany

Posted 24 April 2019 - 09:22 AM

ASPA is time consuming and accuracy is poor. According to the German AVX manual (translated by Baader Planetarium) you have to do a 3 star alignment followed by polar alignment and then turn off the mount and do a 3 star alignment again for a measurement of the polar error. Depending on how well you do this may take 20min to 1h. The accuracy is ok for guided imaging but no way for unguided.

If you don't want a polar scope, watch this at 34:42 https://www.youtube....h?v=zQB6UnrTEEM

This is drift alignment using the camera. It will also take an hour or so but yields a high accuracy. The important thing is to understand the difference between guided and unguided imaging:

- unguided: even a small polar error makes the stars drift a lot. Either you polar align using the drift method or you take very short subs

- guided: (talking about guiding both axes) the drift is gone, the position of the guide star is nailed. Now the polar error results in a very slow rotation of the field, in most cases not relevant even with 10min subs. ASPA is sufficient in this case. If you are not guiding use the drift method or a software like SharpCap. You will need to guide anyway, so get yourself a guidescope and a polarscope. With that combination the polar alignment is done in less than one minute.


  • Juno18 likes this

#5 StarmanDan

StarmanDan

    Aurora

  • *****
  • Posts: 4627
  • Joined: 27 Aug 2007
  • Loc: Where the stars at night are big and bright...

Posted 24 April 2019 - 07:31 PM

I use the DARV method for polar alignment using my DSLR.

https://www.cloudyni...bert-vice-r2760

APT has a nice feature that assists with this and once you get the hang if it, it goes rather quickly. I now use sharpcap and my guider camera and guide scope for polar alignment. Much faster and more accurate.

#6 kathyastro

kathyastro

    Viking 1

  • *****
  • Posts: 558
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 24 April 2019 - 08:02 PM

Hello everyone.

I started into astroimaging several years ago but like many others I started too big, got frustrated and had to step back and take a sabbatical. I missed it terribly so I regrouped and 

I started up again, slowly this time. I obtained an iOptron Skyguider Pro and a WO ZS61 refractor with a WO field flattener and a Canon t3i fir imaging.  After about a year of practice and learning getting pretty good results I wanted to move up to something that would allow me longer exposures so I upgraded to an AVX mount and started using EOS Backyard. However I am a little confused, perplexed and downright nonplussed about the 2 star and ASPA. The posts I read all deal with using a polar scope and eyepiece. I am blessed with having a clear view of Polaris and since the Canon is live view I have been able to center Polaris in the crosshairs on the EOS Backyard program.  My question is, since the t3i is part of the imaging train, it should be seeing exactly what the Z61 is seeing correct? And if so, this would eliminate the need for a polar scope and/or eyepieces. I can just use the live view to do my star alignments. Am I missing something here?

Thanks in advance for all your help. 

Learn to use a polar scope.  ASPA and equivalent software routines have their place, but apparently do not do any better than a polar scope does.  The polar scope is fast and easy once you learn to use it.  It is also quite accurate enough tof 1-minute subs at 800mm focal length.


  • TelescopeGreg and Juno18 like this

#7 TelescopeGreg

TelescopeGreg

    Viking 1

  • -----
  • Posts: 899
  • Joined: 16 Jul 2018
  • Loc: Auburn, California, USA

Posted 24 April 2019 - 10:38 PM

Learn to use a polar scope.  ASPA and equivalent software routines have their place, but apparently do not do any better than a polar scope does.  The polar scope is fast and easy once you learn to use it.  It is also quite accurate enough tof 1-minute subs at 800mm focal length.

+1

 

Get the polar scope and one of the many free smartphone apps (I use PolarisView) that tell you where Polaris should be on the circle.  Mechanically put Polaris in that spot, and you have your polar alignment done.  Don't bother with trying to interpret where the constellations are in the polar scope's reticule.  That's pretty much useless.  I often have to remove (unscrew) the polar scope in order to get the mount aimed close enough to have it with the scope's field of view, then put it back in and go from there.

 

Once the mount is polar aligned, I do a "quick align" on the hand controller after verifying the date and time.  There's a menu item to enable the realtime clock; the default from the factory is OFF.  Doing the quick align starts the rotisserie running, so you're not fighting moving stars during the star alignment.  Makes things a lot less stressful!

 

Then I pick a bright star about half way up in the sky and halfway back on, say, the west side of the scope, and use a sky mapping app (I use SkEye on the phone) to figure out (or verify my guess) what star it is.  Tell the hand controller to go there, and then use the hand controller arrow keys to put that star dead center in the middle of the eyepiece.  I use a "reticule eyepiece", but using the DSLR's Live View can work too.  I also have a much better time getting the chosen star to be within the field of view of the eyepiece by using a Telrad finder (easier than using the magnifying one that comes with the scope) to get the scope close first.  The keys Motor Speed, 7 put the scope in a high rate to get it there, then Motor Speed, 4 to fine tune it within the eyepiece.  When it's centered, push Back a few times to get back to the main menu, then Align, Enter, Enter, and Align (I think that's the sequence) to capture that star as an Alignment star.  Do the same procedure with another star on the other side (east, in this example).  Now do it again for a 3rd star (you can be on the same side as the last alignment star), but this time instead of Align and enter, push Align, then the Scroll Down (9) key to select Calibration instead of Alignment, and follow that through.  Then flip back over to the other side and do it again for a second calibration star.  That usually gets the scope calibrated well enough that an arbitrary GoTo operation will put your target pretty close to center of the eyepiece.

 

That last section was a big mystery to me initially, as folks were telling me to "do a 3- or 4-star alignment", but only two alignment stars are allowed.  The others aren't alignment stars, but calibration stars.  Sheesh...

 

Now, if you've done all this with some precision, you're all set to go.  You can add two more calibration stars if you want.  I sometimes do that with a star near my target, just for a little more precision if the target is one I can't see exactly in the eyepiece or in a quick image with the camera.  I usually use that last calibration star with a Bahtinov mask to focus the camera, then slew to the target and start snapping images.

 

Good luck!



#8 proud clamper

proud clamper

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 26 Mar 2016
  • Loc: Reno, Nevada

Posted 25 April 2019 - 12:22 AM

Thanks everyone for your responses. It is a great feeling to know there is always someone there to lend you a hand. I hope in time I will be able to pass it forward.


  • wrnchhead likes this

#9 the Elf

the Elf

    Surveyor 1

  • *****
  • Posts: 1595
  • Joined: 06 Sep 2017
  • Loc: Germany

Posted 25 April 2019 - 03:33 PM

No need for an app. Use your eyes! Find polaris and kochab. Kochab is the second brightest star in ursus minor, beta UMI. It happens by chance that polaris - NCP - kochab are in a straight line. The polar scopes gives you an upside down view. Look at the sky. Say you see Kochab at the 2 o'clock position when polaris is the center (10pm this time of year). Put polaris at that position in the polar scope. Done. Very easy.


  • proud clamper likes this

#10 wrnchhead

wrnchhead

    Viking 1

  • *****
  • Posts: 884
  • Joined: 28 Aug 2017
  • Loc: NE Kansas

Posted 25 April 2019 - 03:49 PM

I have been using the painful ASPA on my AVX, (the full 2+4, power down and 2+4 again) and it does indeed take about an hour. From my yard it's especially difficult because I have to pick where to put my scope for a target, avoiding trees, lights etc. Then invariably the alignment stars are all (it has to be a conspiracy) behind tree branches.

 

I searched polemaster and here I landed. Would gladly pay the $200ish to have a simpler polar alignment procedure. My polar scope +phone apps does get me close, but since I'm new to imaging, I try to do every step 100%. 

 

I have not used sharpcap or the routines in PHD yet. WIth so much learning to do I haven't experimented with being smarter than the software. 



#11 kathyastro

kathyastro

    Viking 1

  • *****
  • Posts: 558
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 25 April 2019 - 04:50 PM

 

My polar scope +phone apps does get me close, but since I'm new to imaging, I try to do every step 100%. 

 

Your polar scope should do better than "close".  With it alone (and the app to tell you where Polaris should be), your alignment should be good enough for 1-minute unguided subs.  It shouldn't take more than a couple of minutes. 

 

If you want better alignment than that, drift alignment is the way to go.


Edited by kathyastro, 25 April 2019 - 04:51 PM.

  • wrnchhead likes this

#12 wrnchhead

wrnchhead

    Viking 1

  • *****
  • Posts: 884
  • Joined: 28 Aug 2017
  • Loc: NE Kansas

Posted 25 April 2019 - 04:58 PM

Ok great, I will look into drift aligning and feel a little relief that my workload is not so high, thank you Kathy!

#13 Juno18

Juno18

    Explorer 1

  • *****
  • Posts: 72
  • Joined: 07 Dec 2018
  • Loc: Long Beach, Mississippi, USA

Posted 25 April 2019 - 05:08 PM

The polar scope works well. As does Sharpcap. I get it close with the polar scope (1 minute) at dusk, then when it’s dark, I use Sharpcap (5 minutes). 

If your AVX is anything like mine (and a bunch of other people), there is a ton of DEC backlash. 

As long as you are guiding with with a bunch of backlash, the PHD folks recommend getting PA close (degraded by up to 5 arc min) and guide DEC in one direction (N or S). Works pretty well.

 

 Thanks,

Jim


Edited by Juno18, 25 April 2019 - 05:09 PM.


#14 wrnchhead

wrnchhead

    Viking 1

  • *****
  • Posts: 884
  • Joined: 28 Aug 2017
  • Loc: NE Kansas

Posted 25 April 2019 - 05:36 PM

Last weekend went back through my AVX's mechanicals and the guiding last night was averaving 1.5 arcsec, which had me ecstatic. I have half the money squirreled away for the eq6r, cannot wait. (Please tell me to not get the ASI1600mm first! haha) 

 

Clamper, thank you for letting me get a couple questions answered in your thread, not my intention to take it over. 


  • Juno18 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics