CGEM Drift Alignment Procedure

Ray,

Great job in keeping the drift alignment simple. Thanks for the guide, appreciated!

Jeff,

Thanks for the feedback!

Ray

Ray,

I am still waiting to test out my new mount. I have been working alot of hours and one of scopes are at a friends house in his observatory. Between his hours and mine it has been difficult to time things out to grab the scope. The weather here in Western Ma, has also been horrible. I am planning on hopping into some quick widefield imaging right away. Will post how I make out. Hopefully, this weekend I can pick up my scope. I am looking foward to trying out your procedure. Keep the reviews coming it is hard to find good reviews out there and practical stuff for this mount.

Hi Ray,

Looks like one of the best set of directions I’ve seen for polar aligning a GEM. I have a SkyWatcher EQ-6 mount which is their name in Canada/ while in the US, they are known as Orion Atlas.

I believe they make the same mount as the Celestron. Anyway, I’ve been struggling with the instructions given in the accompanying SkyWatcher manual, I think yours will do the trick nicely.

Now . . . if it would only stop raining.

Thanks again,
Rob.

q

Ray,

I finally had a chance last week to setup, it was a last minute setup decided while I was on my way home from work. I had to run up to a friends house to pickup my scope so I could get it mounted.

It was dark when I began but overall things went very smooth. I was not prepared when it came to equipment. I have been working on some home renovations and my equipment is located between 5 various rooms in the house. I was able to align very quickly but could not find my higher power eyepieces they are around hiding somewhere. The alignment process went smooth and I was setup and aligned in under 15 minutes. Since I could not find where I placed my eyepiece set I did some visual observing with my 35 panoptic and 20mm nagler which were in another case through my meade 80mm ed 5000 apo…..very nice views. I was very impressed with the mount from my initial quick setup. I am hoping some of my projects at house will wind down soon so that I can get some more time in and get reorgnized. I have a week off coming up later this week hoping I may get a break in weather to set up for some imaging looks to be rain beginning of that time off. I followed your guides without any issues, best I have seen yet. Keep up the articles I look forward to them.

J. Turner

Hi all,

Thank you for this great review, I just need to understand something, when I used your drift align procedure what is next? I mean will the object be centred for long time? how long?
On the other hand, do you think it’s worth to get? please advice me.

Please forgive me because of my poor English.

Again thank you very much sir.

algady

Hi Ray
If I understand you correct, that means those several minutes are enough for good exposure time ?

In general, dose that mean that CGEM is NOT accurate enough? if yes is that an issue? or that is normal in most mounts.

finally, what did you mean by unguided astrophotography?

Thanks Mr Ray for your patience.

Regards

Hi, Ray:
I have the same CGEM and bought the Polar finderscope [this finderscope can also be used for CG-4 mount & CG-5 Advanced mounts. this sentence is said in its manual]. But I am so confused with this manual.

After I setup the finderscope, look through it and can see the pattern: Big Dipper is at 12:00; Cassiopeia is at about 6:00. In its manual, it lets me rotate the mount until one of the pattern matches the real constellation, (http://www.celestron.com/c3/product.php?CatID=16&ProdID=526) please see this address and this is the manual.

If I do as the manual, i.e., in 22nd Nov., Big Dipper is at 6:00 position in the actual sky, I have to rotate the CGEM 180 degree to match the actual constellation. But this makes the OTA touch the tripod,. ….

Ray, now I am so confused about the discription in the finderscope’s manual. Please give me help~~~~~

Looking forward to hearing from you~~~~
Please send a letter to my E-MAIL. lidong2221@sohu.com

Thank you!

Hi Conor,

I don’t normally start the polar alignment over. I do a pretty good drift alignment then I go to autoguiding which I talk about here: http://www.astrophotography-tonight.com/orion-starshoot-autoguider-review/. This made a big difference for me. I would say until you get into autoguiding though to just follow the procedure for the All-Star alignment and then do the drift alignment to refine it further. Also, make sure that you balance your mount in both axis for the area of sky that you are imaging in. This should help a lot.

Hi Pat,

I believe what you are reading is true. When you make an adjustment for drift, the star moves away from the center. Then you bring it back with the hand controller to watch for more drift. The better you get the drift corrected, the longer it will take to drift away from the center.

I work with Jeff Turner at http://www.daltonskygazer.com on some astrophotography related projects. He has more experience with PEC on this scope than I do so I’ll add his comments about the subject:

“I do believe that nexremote can retain pec correction. The problem with pec correction is that these scopes use a worm gear. Every 7 or so minutes the worm goes through one full revolution, even which pec correction there will always be one spot that has a bounce on the graph for pec once every revolution. The pec will help tame the scope yes, but ultimately one would want to autoguide this mount. I think a well trained mount with superior polar alignment could get up to 3 min exposures in ideal conditions but not when one breaks down and sets up all the time”.

I’ve been using guiding so I didn’t get into pec. Jeff had some experience with it. I hope this helps!

Thanks,

Ray Shore

I have decided to bite the bullet and have ordered the bits to go guiding! (Unfortunately, no girl.) I am hoping that after the software polar align I can find a guide star, get the guider going, and start imaging. Hopefully, this will sidestep the drift alignment so that i can turn this time into imaging time.

Any comments? Tips on guiding?

I plan to use every chance, during the short summer nights, to get in some practise with the new gear.

Thanks for your help.

Pat

Kenn,

I have noticed the same thing. When I first turn on the CGEM, it does not track until I do a star alignment. My LX200 would track when I first turned it on. I will ask someone about this and let you know.

The southern star doesn’t necessarily need to be a Dec of less than 0. As long as it’s close to the meridian and celestial equator. Some use a Dec of around +20.

Thanks, Ray Shore

After a few go arounds with Celestron they finally answered the question: A drift alignment requires that the mount axis of rotation be precisely orthagonal with the celestial pole. The CGEM has a latitude scale but you should not rely on the reading of 34 degrees. Use a angle reader to verify that the vernier is accurately reading the altitude on your CGEM. Also use the All Star Polar Alignment feature that is available with the mount.
The CGEM requires at least a one star alignment to activate tracking.
Do a two star alignment , followed by the ASPA and then one or two calibration stars. After that try the drift method.

Thanks for being there.
Cheers, Kenn

Hi Ray,

Do you think it would be easier to simplify the procedure such that:

For the Alt adjustment, turn the adj. knob such that the east/west star is being brought back to the center line.

For the Az. adjustment, turn the knob such that the zenith star is being brought back to the center line

I tried to use your directions and they were incorrect. When aligning on a Southern Star (Part II), the star drifted to the right and I turned the azimuth adjustment knob on the west side of the CGEM clockwise. This only increased the drift rate! The increase in drift rate was so subtle that it took me quite a while to figure out what was happening.

Then I read the posted comments and saw where someone said your directions are only correct sometimes (depending on which side of the mount the OTA is positioned). That was frustrating!

I would suggest updating your procedure, which is useful as is, but can be improved.

Also, from a previous comment: Adding a GPS module to your mount will not significantly improve the ease of alignment. All the GPS module does is provide accurate time and location information to the controller. If you can enter accurate date/time/lat/long info in to the hand controller manually, then the GPS module becomes an unnecessary, and overly-expensive accessory.

Finally, if you are going to update your article, I would suggest including information about where in the setup and alignment process the drift align belongs. Here is what I do:

Orient the mount toward the celestial pole. If in the northern latitudes, verify that Polaris is roughly centered in the polar axis port.

Turn on the mount, enter/verify that the date/time/lat/long are correct.

Do a Two Star alignment. This is just to roughly orient the mount to the sky. This needs to be repeated whenever the mount’s orientation is adjusted with the azimuth and altitude knobs.

Perform the hand controller’s Polar Alignment routine.

Unsync from the alignment star.

Slew and center on each of the original alignment stars, and replace them in the alignment. This is only to make it easier to use the hand controller to find the named stars to be used for the drift alignment.

Now, perform your drift alignment procedure.

After the Drift alignment is successfully accomplished you should once again update the positions of the 2 original alignment stars, and add 2 or more calibrations stars.

One final note: In order to use the azimuth adjustment screws to move the mount, it may be necessary to loosen the Mounting Knob (the knob that is attached to the bolt that fastens the mount to the tripod). Loosening it too much will make the mount unstable (wobbly) and it will be nearly impossible to accurately align the mount. You will know that this is the case if the field of view changes as the knob is finally made hand tight. Having the knob totally hand tight will make it very difficult to push the mount with the adjustment screws. Play with it a bit to find the “sweet spot” before performing the Polar Alignment and/or the drift alignment steps.

Those are just my thoughts. I hope that they help.

Rick