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

EQ6R pro Tracking issues or just poor polar alignment?

mount
  • Please log in to reply
5 replies to this topic

#1 DAVX

DAVX

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 03 Apr 2020

Posted 06 April 2020 - 06:04 PM

Hello friends!  Im David from Chile

 

Like 1 month ago i bought an EQ6R Pro mount, and because the low amount of good subs that i get with it, im thinking that my mount is not ok. 

 

My equipment:

 

EQ6R pro

ES ED102 APO FCD100

Canon 600D

Deep Cycle Battery 33Ah (to power the mount and camera)

Perfectly balanced

NO autoguide system yet...

Sharpcap polar align

 

Let me explain, in a normal night i try to get like 200 to 300 subs of 60s of exposure, but just 50 to 70 of them are usable, with an "ok" tracking accuracy, i know that this mount can track "ok" for like 1 to 3 minutes without guiding but, seems impossible to me to get exposures any longer than 60s. 

 

Saturday night i try to do some captures to see the tracking accuracy of my mount, so i test five different exposures two times each at 60s, 90s, 120s, 150s, and 180s. (i did a polar align with sharpcap, and get like 2" error)

 

these are the results (you can zoom it to see the details): https://ibb.co/WpMh9G6

 

As you can see, the tracking at each exposure time was not consistent, some pictures have better tracking than the next one at same exposures, and some are like if the mount was tracking ok, and suddenly make a jump and keep tracking ok again (like the first at 120s and the second at 180s), if this drift was only by poor polar alignment I think that the star trail has to be in all the frames and look like a perfect line, not like my pictures.

 

what do you think???

 is only a poor polar align issue?? or something is bad with my mount??

 

thanks in advacne for your answers!

 

im, not a native speaker so my English may be not so good sorry for that.

 

 



#2 jdupton

jdupton

    Mercury-Atlas

  • *****
  • Posts: 2,516
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 06 April 2020 - 06:40 PM

David (DAVX),

 

   Since you say you were not guiding, I will assume that the camera is oriented such that East / West is the vertical direction. Does that match what you think?

 

   Under that assumption, I would say this is likely from one of two causes or both:

  • Periodic Error (PE) in the drive train. This is often fairly normal and expected to one degree or another with mounts.
     
  • Telescope balance is too good. You should try to achieve slightly East-Heavy balancing.

    You might want to repeat this test and make the telescope slightly off-balance in the RA (East / West) axis. Whichever part of the scope is on the east side of the mount, make it slightly (but not by a lot) heavier. Example, If you are pointing East with the telescope, the refractor will be on the West side of the mount and the counterweights on the East side. You want to balance so that the counterweight side is slightly heavier. When the refractor is pointing to the West, it will be on the East side of the mount and the counterweights on the West. In this case, balance so that the counterweights are a little lighter than the refractor.

   The PE will naturally cause the mount to have periods during which it drifts east and other periods when it drifts west. On average, it will track at the proper sidereal rate but slight periodic differences in tracking rate will make it "see-saw" back and forth causing trails in the RA directions of the image.

 

   When the mount is balanced too well, it can be "nudged and fall" as it tracks. All mounts have some amount of backlash in their drive gears. This is completely normal for most mounts. The tiniest of gaps in gear mesh means that the mount can "rock" back and forth minutely in either the RA or Dec Axes. When tracking, the motor attempts to push the mount steadily to the West.

 

   If it is balanced too well or if it is balanced slightly to the West, you can have the situation where the motor takes up the slack in the gears and begins to push the mount West. With the tiny gap, this may cause the mount to "Fall" to the West coming to a stop when the gears mesh again. Now however, it has moved too far and must wait for the motor to push drive nothing until it closes the gap in the gear mesh. Then the process starts over again.

 

   This slight nudge from the motor causing the mount to fall West until the motor catches up and starts the cycle again will show up as slight barbell shapes in the trailed stars very similar to some of yours. One end is tracking, the middle is the falling stage and the end is more tracking.

 

   To me, I expect your mount is working as expected. Once you start guiding to counteract an PE and balance the system slightly to East-Heavy, you should see much improved images.

 

 

John


Edited by jdupton, 06 April 2020 - 06:40 PM.

  • GeneT likes this

#3 JPKellysr

JPKellysr

    Viking 1

  • *****
  • Posts: 509
  • Joined: 26 Feb 2015
  • Loc: Genoa, Nevada, USA

Posted 06 April 2020 - 07:39 PM

Poor polar alignment many causes dec errors. Perhaps that info will help.



#4 DAVX

DAVX

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 03 Apr 2020

Posted 08 April 2020 - 02:22 PM

Thanks so much for your replies.

 

As soon as i can i will take my mount outside and try all your recomendations. and test it again!!

 

Thanks!!



#5 JPKellysr

JPKellysr

    Viking 1

  • *****
  • Posts: 509
  • Joined: 26 Feb 2015
  • Loc: Genoa, Nevada, USA

Posted 08 April 2020 - 08:24 PM

Get the QHY or iOptron  polar cameras. You will have amazing good polar alignment.



#6 Tapio

Tapio

    Mercury-Atlas

  • -----
  • Posts: 2,791
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 08 April 2020 - 08:34 PM

1 minute exposure with that mount and that focal length is not bad without autoguiding.
I think you should not worry more about better polar alignment.
If you want longer exposures consistently just get autoguiding working.
It's no big deal.


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





Also tagged with one or more of these keywords: mount



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics