Home Part 3 of my review covers polar alignment of the CGEM. I actually used two different methods. First, I just had to try the new “All-Star” polar alignment routine that Celestron has been touting. Then, I fine-tuned it with a standard drift align.
To get set up, the polar axis of the CGEM must be pointed close to the celestial pole. Since I’m in the northern hemisphere, I pointed it toward Polaris, the North Star. The first step though was to set the latitude scale of the CGEM. This is a simple adjustment to the latitude adjustment knobs.
Click to Enlarge Photo of CGEM
Basically, I adjusted the angle to correspond to my latitude here in Kansas. Here is a handy tool on my other site to find the latitude for various cities in the U.S.
Once the CGEM’s latitude is set, then it’s a matter of aiming the polar axis of the CGEM toward the celestial pole. I can see Polaris from my backyard so I first eye-balled the alignment by adjusting the CGEM so the RA axis was aimed at Polaris (as shown below).
Next, I leveled the mount with the handy bubble level that is built in. Then I removed the polar finderscope covers and adjusted the azimuth and latitude adjustment knobs until Polaris was centered. Note that I do not have a polar finderscope; I just centered it the best I could through the hole where a finderscope can be inserted. This made it close enough to perform the All-Star polar alignment.
All-Star Alignment of the CGEM
Before starting the All-Star alignment routine, a two-star aligment must be performed first. I covered this in Part 2 of my CGEM Review. This has become a fairly simple task since I’ve done it a few times.
After the two-star alignment is complete, then the All-Star alignment can be initiated. First, a star must be selected from the “Named Star” database list in the hand controller. When a star is selected, the CGEM will automatically slew to the star. When the command is given to align the mount, the CGEM actually slews a short distance away from the star then it slews back. The star must be centered in the finderscope first and then in the eyepiece. It is helpful to use a reticle eyepiece to get the star centered exactly in the middle of the eyepiece. The one I use specifically is the Orion 12.5mm Illuminated Reticle Plossl Telescope Eyepiece. Once the align button is pressed, the CGEM will sync on this star then slew to the position that it ”should be” if it actually was polar aligned. Then it’s just a matter of adjusting the latitude and azimuth knobs to center the star in the eyepiece. It is important here not to center the star by slewing with the hand controller. The “mount” must be adjusted to be properly aligned with Polaris.
Tips for Polar Aligning the CGEM
- During the All-Star alignment routine, the hand controller will warn you not to choose a star near the meridian or one that is on the eastern or western horizon. I of course chose my first star on the meridian and I could not get it centered in the eyepiece! After moving it to a star between the meridian and the western horizon, it was easy to center the star.
- Use a reticle eyepiece to center the star exactly. The following is a good choice: Orion 12.5mm Illuminated Reticle Plossl Telescope Eyepiece
- If the star is not visible in the eyepiece during mount adjustment (i.e., adjustment of the latitude and azimuth knobs), use the viewfinder for a wider field of view and center it there first. I figured this out my first time after working like mad to get the star to show up in the eyepiece. The light bulb finally came on and I used the viewfinder first. Then the star was visible in the eyepiece!
All-Star Polar Alignment Result
I found that this new polar alignment routine did a pretty good job for a quick and close alignment. To test the accuracy, I put the telescope on Jupiter and tested the tracking. It held really well in lower power eyepieces like 30mm and 25mm. But Jupiter started to slowly drift out of the field of view with higher powers such as 10mm and 5mm. This may get better once I get more experience with the All-Star polar routine though. For my first trial, I thought it worked well to get the CGEM closely aligned!
CGEM Drift Align
As mentioned at the beginning of my review, I fine tuned the polar alignment with a traditional drift align. Basically, I found a star in the southern part of the sky (near the meridian) and did the first part of the alignment which invoved adjustments to the azimuth knobs until the star stopped drifting. Again, I utilized my 12mm reticle eyepiece.
Then, I pointed the telescope at a star close to the western horizon and adjusted out the drift with the altitude adjustment knobs.
I may write up a detailed procedure on how to perform a drift alignment on the CGEM (especially if I get a lot of requests for it!).
Drift Align Result
My test on Jupiter was a sucess! The CGEM kept Jupiter centered quite nicely in higher power eyepieces for several minutes. I think the CGEM will work very well for tracking during astrophotography. I hope to be getting to this stage very soon. I think the Canon Digital Rebel needs to get back to work now!
If you have any questions or comments, please post them in the “Leave a Reply” section below. Also, I have added a survey below to find out if this review was helpful to you.
Clear Skies! Ray Shore
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Comments
Posted On
Oct 10, 2009Posted By
Jeff TurnerRay,
Enjoying reading your reviews keep them coming. A detailed alignment procedure would be great! My new CGEM arrived last week. Waiting for my edge800hd ota to arrive and will be hopping into imaging as soon as possible. I have already changed out the plastic knobs for the aluminum orange anodized. Initial indoor testing of the mount so far has been flawless. Waiting on several cables to arrive to test out my computer hook up. Reviews on imaging and setup with computer would be greatly appreciated!
Clear Skies
J. Turner
Posted On
Oct 10, 2009Posted By
Ray ShoreHi Jeff,
Thanks for your feedback! Nice that you chose the edge800hd. That is an interesting OTA. I thought seriously about getting that instead of my 9.25″ standard SCT, but couldn’t wait until next year for that size to be available. Would be good to hear how your edge800hd is working out for you.
I’ll continue to work on more reviews of my CGEM. I just got a USB to RS232 cable the other day so I can operate the CGEM with my laptop. I haven’t had a chance to try it yet though. But I’ll be sure to post my results along with a tutorial for the drift align.
I wonder if most people are finding that a drift align is a neccessary follow-up to refine the All-Star alignment when the CGEM is used for astrophotography? Will have to check into this.
Congrats on receiving your CGEM. You’re going to like it!
Thanks,
Ray Shore
Posted On
Oct 12, 2009Posted By
Jeff TurnerRay,
Thanks I will keep you updated with my experiences with new setup. I have included the link to machine shop which provides the new orange anodized knob set for the CGEM. I received the knobs within two days of ordering very quick and efficient service. It took me about 5-10 minutes to replace all plastic knobs on my new mount and looks great with celestron orange anodizing.
http://www.admaccessories.com/Miscellaneous_CGEM.htm
Posted On
Oct 12, 2009Posted By
Ray ShoreThanks Jeff for posting that link. Those orange anodized knobs look awesome on the CGEM. Looking forward to your updates!
I need to look into a saddle through ADM so I can mount my ED80.
Posted On
Oct 19, 2009Posted By
Jim PecorellaThanks for your reviews. I have been looking for a new telescope mount for my Meade 2080 GEM SCT. I have read a lot of reviews concerning telescope mounts and concluded that the CGEM will probably work best for me. Your articles convinced me that is the way to go. Thanks.
Please add another article regarding the drift alignment procedure.
Posted On
Oct 20, 2009Posted By
Ray ShoreJim,
I’m glad my CGEM reviews are useful to you. One of the reasons I wrote them is because I had troubles finding reviews on them when I was trying to decide.
I’ll be sure to write a tutorial on drift alignment.
Thanks,
Ray
Posted On
Nov 02, 2009Posted By
Steve WrightRay,
I, too, have found your CGEM journey to be very useful. I’m seriously considering matching the CGEM up with a f4.1 Borg 101ED. Your comments are supporting this plan, but I would love to hear more (and I’ll vote for the drift align tutorial, too!).
Cheers,
Steve
Posted On
Nov 02, 2009Posted By
Ray ShoreSteve,
The Borg and CGEM would be an interesting setup. If you go with this combo, would love to hear how it is working out for you. DSLR imaging in mind?
I still need to mount my ED80 on the CGEM and try some astrophotography with the Canon Digital Rebel.
By the way, I just posted my tutorial for the CGEM drift align: http://www.astrophotography-tonight.com/cgem-drift-alignment-procedure. I hope it is helpful!
Thanks,
Ray
Posted On
Nov 03, 2009Posted By
SteveRay,
Shortly after I posted my note I found your tutorial (man, your fast!). But seriously, I think it’s a valuable contribution; simple, straightforward. I’ll try it out!.
I currently have a wedge-mounted CPC800 that I’ve been using with Hyperstar. I like it a lot, and have had some reasonable success with my initial forays into astrophotography (I’m using a QHY8; my Nikon D40X is not really applicable). I figure to use the CPC800 on the CGEM, mounting the BORG as a guidescope, giving me the option to use either as the imaging scope with the other serving as guide. At least, that’s the plan.
I’m in the final phases of building a small observatory so I can keep the kit set up. rather than breaking it down every night. The roof should be up within a month or so (work is slowing things down…).
I’m rambling. Again, thanks again for your contributions. I’ll check back from time-to-time to gauge your progress.
Cheers,
Steve
Posted On
Nov 04, 2009Posted By
Ray ShoreSteve,
In order to use your CPC800 as a guidescope, will you have to use a focal reducer? I’m thinking about something similar where I piggyback my ED80 to my 9.25″ SCT on the CGEM. Then I could use either as a guidescope or imaging scope.
Glad to hear my CGEM drift align procedure is a valuable contribution
Thanks,
Ray
Posted On
Jan 15, 2010Posted By
SplineyThanks (again
) for these articles so far, Ray. Also I am glad you decided to write a tutorial on the CGEM drift alignment! Thumbs up!
Robert
Posted On
Jan 16, 2010Posted By
Ray ShoreRobert,
Thanks again for the feedback! More articles to come.
Ray Shore
Posted On
Mar 22, 2010Posted By
JohnRay,
PLEASE post something on the CGEM drift alignment. I’m pulling my hair out trying to figure this out. I even have PHD and do autoguiding and cannot keep any pics over 60 seconds due to drift
Please, please, please!!!
John Preston
Rochester, MN
Posted On
Mar 22, 2010Posted By
Ray ShoreHi John,
I’ve got it covered on CGEM drift alignment: http://www.astrophotography-tonight.com/cgem-drift-alignment-procedure. Please let me know how it works.
Thanks,
Ray Shore
Posted On
Apr 25, 2010Posted By
joseHi Ray,
Can the CGEM mount work a lower latitudes (10º degrees)? The GT mount has 2 tricks: 1) remove front latitude adjustment knob; 2) rotate mount 180º.
In GGEM mount, the front latitude adjustment knob doesn’t seem to coming into contact with the R.A. motor assembly. The mount is already rotate 180º (GT mount has 1 leg north and CGEM has 2 legs north).
Celestron support team says that I can use GT mount tricks but I can’t see that.
thanks,
Jose
Posted On
Apr 25, 2010Posted By
Ray ShoreHello Jose,
At first I thought that it would work at 10º degrees latitude but the user guide says that the CGEM altitude can be adjusted from 15 to 70 degrees.
Regarding the legs, the alignment peg on the CGEM tripod can be turned to the other side so that there is one tripod leg facing north. This is how mine is setup because it fit in my observatory better.
Not sure how you get the CGEM to work at 10º degrees latitude though. Can you explain further what the mount trick is all about?
Thanks,
Ray Shore
Posted On
Apr 25, 2010Posted By
JoseHi Ray,
The trick is for the GT-5 mount. 1) Put 1 leg to south in order the counterweight bar doesn’t touch a leg (CGEM has 1 leg to south). 2) Remove the front latitude adjustment screw in order the r.a. mount doesn’t make contact putting a lower latitude.
Thanks,
Jose
Posted On
Apr 26, 2010Posted By
Ray ShoeJose,
So according to Celestron, the CGEM can be lowered to 10º by removing the front latitude adjustment screw completely. This is good to know.
Thanks,
Ray Shore
Posted On
Apr 27, 2010Posted By
JoseHi Ray,
This is a good news. Thanks Ray.
Celestron wrote me today “Our Alt-Az Goto mounts can be wedged for latitudes less than 10°”. That is not a contradiction with your answer because they are talking about “less than 10°” and not “exactly 10°”. I feel like I’m talking with a lawyer when Celestron answers my questions.
Thanks
Jose
Posted On
Apr 27, 2010Posted By
Ray ShoreJose,
I don’t know that the CGEM can be lowered to 10° unless it is by the trick you mentioned. I have not verified this myself. But the Alt-Az mounts are different than the CGEM which is equatorially mounted. Why did Celestron mention the Alt-Az mounts I wonder?
Thanks,
Ray Shore
Posted On
May 01, 2010Posted By
EdRay,
I wonder if after the All Star Polar Alignment you went back and did the two star alignment as suggested in the Celestron Manual. I guess that would not have made any difference, except to the Go To performance. Correct me if I am wrong, but I think you are right – the two star alignment affects Go To performance, and the Polar Alignment affects drift after you line up your target.
Posted On
May 02, 2010Posted By
Ray ShoreHello Ed,
Correct- the two star alignment does affect goto performance. And if you do at least one calibration star afterwards, your goto performance gets much better. Also correct on the polar alignment- the better your alignment, the less drift you will have.
Thanks,
Ray Shore
Posted On
Jun 06, 2010Posted By
JonRay,
What weight would you feel safe using on the CGEM for CCD imaging – the main scope, off-axis guide scope with autoguider, and the CCD camera itself?
Posted On
Jun 12, 2010Posted By
Jeffry TurnerJon,
I have approximately 35lbs on my setup and that is about the max I would push for imaging. Ideally i would want to be just a few lbs lighter, but so far my setup is working out well, the key is balancing it very well. Depending upon which portion of sky I am on I usually have to adjust the balance a bit. I try to image only one portion of sky at a time.
Regards,
J. Turner
http://www.daltonskygazer
Posted On
Jun 12, 2010Posted By
Jeffry TurnerJon,
I have approximately 35lbs on my setup and that is about the max I would push for imaging. Ideally i would want to be just a few lbs lighter, but so far my setup is working out well, the key is balancing it very well. Depending upon which portion of sky I am on I usually have to adjust the balance a bit. I try to image only one portion of sky at a time.
Regards,
J. Turner
http://www.daltonskygazer.com
Posted On
Jul 05, 2010Posted By
JohnHello Ray,
The man who can help with setting up/ modify mounts to work on /at the Equator will be Albert Lim This is his contact Wish you clear skies, John
Albert Lim”s Office Address :
Astro Scientific Centre Pte Ltd
21, Jurong Town Hall Road, Omni-Theatre, Singapore Science Centre,
Singapore 609433 Tel : +65 65674163 Fax : +65 65674826
E-mail : sales@astro.com.sg
Website : http://www.astro.com.sg
Ps I hope this helps john
Posted On
Dec 21, 2010Posted By
Alfredo BeltranHi Ray
I live in Bogota, Colombia and my latitude is 4.8 deg north. I currently own a Celestron NexStar 6SE and I use it on a home-made equatorial wedge.
Since I’m into astrophotography, I’d like to upgrade my mount and the CGEM would be the perfect choice because of the PEC and the All Star Polar Alignment routine (Polaris is not always seen from my site).
But I have to be sure that the CGEM can be used at this low latitude. So, I’m interested in the discussion of using it below 15°.
So I have two questions:
1. Do you think it is possible to use the mount safely by tilting the tripod’s two north legs in order to reach my 4.8°?
2. Can the All Star Polar Alignment routine be used with the mount tilted?
Your help will be highly appreciated.
Best regards,
Alfredo
Posted On
Dec 22, 2010Posted By
AstroPhotography TonightHi Alfredo,
1. I’m really not sure if it would be safe to tilt the mount like that.
2. The CGEM should be level for the All Star Polar Aligment routine. Thus, I think that it should not be tilted.
However, to be sure, I recommend contacting Celestron. They will know whether you can make the CGEM work at your latitude.
Thanks,
Ray Shore
Posted On
Dec 28, 2010Posted By
Alfredo BeltranHi Ray
I contacted Celestron and they said that the CGEM could be used tilted for astrophotography. I’ll keep on finding out before making the decision.
Best
Alfredo
Posted On
Apr 14, 2011Posted By
Tom NarwidRay
I read your review on the CGEM. Excellent! hanks
TomCan you tell me a little about running the mount with a laptop. What would be a good program. Also what would be the connections on bothe ends i.e the laptop and mount.
T
Posted On
Apr 26, 2011Posted By
Chris PartsenidisDear Ray,
Congratulations on a very well made site with excellent information for us CGEM users. As a owner of a CGEM, I have learnt more about the mount from your tutorials and then actual manual itself!
Please do keep your articles coming as they we look forward learning from your experiences.
I look forward to your detailed Drift Alignment procedure and more tips on getting the most out of the CGEM mount!
Keep up the great work!
Chris Partsenidis – Thessaloniki, Greece
Posted On
Apr 26, 2011Posted By
AstroPhotography TonightHello Chris,
Thank you for the very nice feedback! It is well appreciated. I plan to post more articles on the CGEM. It has been a great telescope!
Ray Shore