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.
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!
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Clear Skies! Ray Shore