Jump to content


Photo

CGEM GoTo accuracy

  • Please log in to reply
24 replies to this topic

#1 Taylor

Taylor

    Viking 1

  • *****
  • Posts: 828
  • Joined: 10 Jul 2005
  • Loc: Owasso, OK

Posted 23 July 2009 - 03:48 AM

For you CGEM owners out there, what is the GoTo accuracy of your mount? And what is the alignment process you have to go through in order to achieve that level of accuracy?
I have been previously spoiled rotten with a Nexstar GPS 8" scope which had the most simple, accurate GoTos I've ever had the pleasure of using, and that was with two alignment stars.

Just curious if I could expect the same performance from the CGEM.

#2 waassaabee

waassaabee

    Fly Me to the Moon

  • *****
  • Posts: 5132
  • Joined: 26 Nov 2007
  • Loc: Central California Coast

Posted 23 July 2009 - 07:04 AM

The AllStar Polar Alignment routine is very accurate. Level the mount (close is good enough), center Polaris in the boresight, choose (or use the recommended) 2 alignment stars on either side of the meridian, then (up to) 4 calibration stars on the opposite side of the meridian. This will give you very good GoTo's for viewing. But then you can use the AllStar Polar Alignment feature which has you slew to any star and center. The mount then slews to where it thinks that star should be with correct Polar Alignment and you adjust the alt/az on the mount to center your star. Now the mount is Polar Aligned for astrophotography. It is highly recommended that you then do another 2+4 replacing your original alignment and calibration stars. BINGO, Marine sniper accurate GoTo's until you move your mount... Add on an autoguider and you are in business for long exposures.
I start my alignments as soon as I can see Polaris (twilight), and always have some wait time before I start imaging my first target. Very happy customer!

#3 QueueCT

QueueCT

    Vostok 1

  • -----
  • Posts: 152
  • Joined: 25 Jun 2008

Posted 23 July 2009 - 07:14 AM

I agree. I use the same method as Gary and get spot on GoTos. Honestly, I don't even worry about Polaris, just point it roughly north.

John

#4 Luigi

Luigi

    Fly Me to the Moon

  • *****
  • Posts: 5320
  • Joined: 03 Jul 2007
  • Loc: MA

Posted 23 July 2009 - 08:04 AM

The same software is in the CG5ASGT too.

#5 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15557
  • Joined: 06 Jul 2007

Posted 23 July 2009 - 09:31 AM

For you CGEM owners out there, what is the GoTo accuracy of your mount? And what is the alignment process you have to go through in order to achieve that level of accuracy?
I have been previously spoiled rotten with a Nexstar GPS 8" scope which had the most simple, accurate GoTos I've ever had the pleasure of using, and that was with two alignment stars.

Just curious if I could expect the same performance from the CGEM.


Only two secrets.

Add calibration stars (I usually add three - four)

Right and up only for final centering.

The mount is not at all sensitive to polar misalignment when it comes to go-to accuracy.

#6 Lane

Lane

    Soyuz

  • -----
  • Posts: 3591
  • Joined: 19 Nov 2007
  • Loc: Frisco, Texas

Posted 23 July 2009 - 10:02 AM

I recently learned myself just how important the extra calibration stars are. 2 alignment stars and 1 calibration star gets every object into my 40mm lens after a goto. Add 1 extra calibration star and it gets every object into a my 14mm lens after a goto.

Another secret besides adding calibration stars:
During alignment, just before you hit the button to indicate the alignment star is centered, put in a high power eyepiece and center the star in there or use a cross hair eyepiece as some do. Trying to center a star in a low power wide angle eyepiece has never worked out well for me.

The final secret is to replace the calibration stars after a few hours with a fresh set of stars. Easy to do and does not require going back through the entire alignment process. You just select one of the calibration stars (or alignment stars) and replace it with the current object you are viewing. You can even add additional calibration stars to the original ones you input.

#7 NewAstronomer

NewAstronomer

    Soyuz

  • *****
  • Posts: 3909
  • Joined: 03 Sep 2004
  • Loc: Northeast, PA U.S.A

Posted 23 July 2009 - 01:43 PM

I know its not the scope you are asking about, but in the same class (price/weight) is the Atlas. I coupled it with EQMOD, which makes it very fun to image with. And allows me to use any star or object in the sky to sync against as the night progresses.

The initial alignment is :
1) Level using built in bubble level
2) Simple polar align using built in polar scope (I used to drift!)
3) 3 star alignment (I center the scope on the star using a joystick, you can use any gamepad, or the SynScan controller)
4) GOTO's have object on DSI chip visible on my laptop the rest of the night, telescope 420mm focal length

Its pretty simple, first GOTO scope I've ever owned. Before I slew to a new object I make sure object centered on my laptop using Nebulosity's cross hair, right click/telescope/sync in Cartes Du Ceil, and pick new object, boom, scope slews to new object and there it is, every time. For polar accuracy, I've taken sample images up to 120 seconds, stars stay nice and round.

#8 donsinger1

donsinger1

    Ranger 4

  • -----
  • Posts: 307
  • Joined: 28 Oct 2007

Posted 23 July 2009 - 07:03 PM

I agree. I use the same method as Gary and get spot on GoTos. Honestly, I don't even worry about Polaris, just point it roughly north.

John


Count me in too...I use the same procedure, which takes no more than 20 minutes to get aligned, polar aligned, then re-aligned..Polar alignment has been good enough that 5 minute guided images show round stars...I could probably go longer but LP is too bad even with an LP filter.

Also, gotos are spot on..the other night, for instance, after setup and alignment, I focused my CCD on Sadr and then did a goto to The Veil and it was on the center of the CCD chip...never fails

#9 Taylor

Taylor

    Viking 1

  • *****
  • Posts: 828
  • Joined: 10 Jul 2005
  • Loc: Owasso, OK

Posted 23 July 2009 - 07:29 PM

Mmm, sounds just like my Nexstar GPS, I miss it :(

#10 waassaabee

waassaabee

    Fly Me to the Moon

  • *****
  • Posts: 5132
  • Joined: 26 Nov 2007
  • Loc: Central California Coast

Posted 23 July 2009 - 08:43 PM

Mmm, sounds just like my Nexstar GPS, I miss it :(

What are you waiting for? You know you want one... :whistle:

#11 Taylor

Taylor

    Viking 1

  • *****
  • Posts: 828
  • Joined: 10 Jul 2005
  • Loc: Owasso, OK

Posted 24 July 2009 - 02:47 AM

Mmm, sounds just like my Nexstar GPS, I miss it :(

What are you waiting for? You know you want one... :whistle:


Why, money of course!

No seriously tough, I loved the computer on my NS GPS, I miss it when observing. So I'm probably going to go back to Celestron, they have spoiled me.

#12 waassaabee

waassaabee

    Fly Me to the Moon

  • *****
  • Posts: 5132
  • Joined: 26 Nov 2007
  • Loc: Central California Coast

Posted 24 July 2009 - 06:50 AM

Ah yes... the dollar factor! An advantage you'll have is that the surge is over and the CGEM is in stock most places.

#13 Taylor

Taylor

    Viking 1

  • *****
  • Posts: 828
  • Joined: 10 Jul 2005
  • Loc: Owasso, OK

Posted 25 July 2009 - 09:39 AM

Here's another question:
does the CGEM have any backlash? Even when zoomed in and microslewing to center an object?

#14 Taylor

Taylor

    Viking 1

  • *****
  • Posts: 828
  • Joined: 10 Jul 2005
  • Loc: Owasso, OK

Posted 26 July 2009 - 09:04 AM

Does anyone have any comments on backlash on the CGEM?

#15 waassaabee

waassaabee

    Fly Me to the Moon

  • *****
  • Posts: 5132
  • Joined: 26 Nov 2007
  • Loc: Central California Coast

Posted 26 July 2009 - 09:14 AM

Very minimal backlash, if any at all on mine.

#16 donsinger1

donsinger1

    Ranger 4

  • -----
  • Posts: 307
  • Joined: 28 Oct 2007

Posted 26 July 2009 - 11:39 AM

Does anyone have any comments on backlash on the CGEM?


Not noticeable on mine...have not even given it any thought.

Don

#17 Harold925

Harold925

    Vostok 1

  • -----
  • Posts: 134
  • Joined: 11 Jul 2009
  • Loc: Near Charleston, S.C. Cluster

Posted 26 July 2009 - 01:46 PM

Greetings CGEM Owners,

I've spent the money and received my CGEM mount/OTA combo just days ago. After reading the manual, I set up last night aimed at Polaris, aligned with two stars and then aligned three calibration stars, without doing the full polar alignment. My first target was M51 and the mount slewed right to it, along with all the other objects I selected for three hours. I'm having some problem with the tracking, since the objects are drifting out of view after a period of time. Would the full Polar Alignment solve this trouble? Could some of you experienced owners provide a brief as to what I need to fine tune in Tracking and Scope Setup features or any other advice? Thank you.

Harold

#18 Chris Rowland

Chris Rowland

    Viking 1

  • -----
  • Posts: 586
  • Joined: 28 Feb 2005

Posted 26 July 2009 - 05:22 PM

The drift is probably polar alignment inaccuracy. Gotos aren't affected because the calibration allows for this.
Try the new AllStar polar alignment (press the Align button, look for Polar Align and follow the instructions an the HC).

Chris

#19 donsinger1

donsinger1

    Ranger 4

  • -----
  • Posts: 307
  • Joined: 28 Oct 2007

Posted 26 July 2009 - 06:07 PM

That is just drift due to misalignment to the pole.

#20 Harold925

Harold925

    Vostok 1

  • -----
  • Posts: 134
  • Joined: 11 Jul 2009
  • Loc: Near Charleston, S.C. Cluster

Posted 26 July 2009 - 07:27 PM

Hey, I appreciate the replies! I wasn't sure if I needed certain settings in the Tracking and Scope Setup features, since this my first EQ mount. I was surprised at it's performance on the first outing. I have read the manual again and I will execute the All Star Polar Alignment next time.

Regards,

Harold

#21 waassaabee

waassaabee

    Fly Me to the Moon

  • *****
  • Posts: 5132
  • Joined: 26 Nov 2007
  • Loc: Central California Coast

Posted 27 July 2009 - 10:30 PM

Harold, Welcome to Cloudy Nights!! After you do the All Star, unsync and refresh your alignment and calibration stars (it's all in the manual). Then enjoy...

#22 stevecoe

stevecoe

    "Astronomical Tourist"

  • *****
  • Posts: 4263
  • Joined: 24 Apr 2004
  • Loc: Arizona, USA

Posted 28 July 2009 - 02:02 PM

Howdy all;

I had a great time with my CGEM at Table Mountain Star Party for the last week. Once I got all set up, I did the polar align routine, turned off the mount, restarted and did a 2+2 star align and it did not miss all night long. Next night and next and next...it just worked.

This was hauling my 6" f/8 refractor with no trouble. It just found everything in every mode I could throw at it. So, using "M" or "NGC" keys was easy, I enterred the RA and Dec for dozens of double stars and red stars and it found them all.

I am very happy with my CGEM. I did buy the cord extender for the handpaddle and it really helps. Now I can view my observing list while I have the handpaddle in hand. I also bought the large aluminum knobs from Scopestuff, they make it much easier to get a grip on the controls for azmuth adjustment and the scope plate.

Enjoy;
Steve Coe

Attached Files



#23 Harold925

Harold925

    Vostok 1

  • -----
  • Posts: 134
  • Joined: 11 Jul 2009
  • Loc: Near Charleston, S.C. Cluster

Posted 04 August 2009 - 03:45 PM

** CGEM POLAR ALIGNMENT UPDATE **

I appreciate all of your attention and advice, due to my first use with my new mount/scope combo. Since then, I've initiated the polar alignment instructions on two occasions and the mount tracked all targets perfectly. I should've done it the first night out, instead of taking a shortcut. Now if the moon would just leave for a while! Enjoy the views.

Regards,

#24 Kokanee

Kokanee

    Lift Off

  • -----
  • Posts: 3
  • Joined: 28 Jul 2009

Posted 07 August 2009 - 12:41 PM

Hi folks,

how long did it take to do a polar alignment on the CGEM?


Thanks,

Anu.

--------------------

Still researching my gear - nothing bought yet :(

#25 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15557
  • Joined: 06 Jul 2007

Posted 07 August 2009 - 01:37 PM

Hi folks,

how long did it take to do a polar alignment on the CGEM?



2 - 3 minutes using AllStar.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics