Author Topic: Sky Watcher EQ6 vs. Celestron CGEM  (Read 1021 times)

tinlengmmuner

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #15 on: January 11, 2018, 02:05:16 PM »
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The GPS module is only available with the EQ6 in Canada. The one supplied by Skywatcher USA does not include the module


That's unfortunate. The GPS is pretty expensive as an option, even up here if one needs a replacement.
Exactly and the module looks to be something that was made for less than $10, but likely if you had to buy separate it would be much more

quetafulra

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #16 on: January 12, 2018, 03:24:29 AM »
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Yes, same manufacturer (Synta).
This is correct. Synta owns Celestron and Skywatcher. They also OEM the Sirius and Atlas for Orion. The Orion mounts are Skywatcher mounts painted black.

<p class="citation">Quote
The CGEM has computer-aided All Star Polar Alignment (ASPA). You don't have to have a polar scope or even be able to see Polaris. You get greater accuracy than with a polar scope.
I am not sure whether the EQ6 has that feature. It may.
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It does. The procedure for it can be found on page 35 of the manual. link to manual

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I am told that the CGEM has servo motors and the EQ6 has stepper motors. Personally, I trust servos more, but that is not from recent experience; both are probably quite reliable now.
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Skywatcher uses Steppers. CGEM uses Servos. Which is better? I don't know in this case. From memory learned way back when Servo control systems are best for high speed, high torque applications that involve dynamic load changes but require encoders to keep track of where they are and are thus closed loop only. Stepper control systems are best for applications that require low-to-medium acceleration, high holding torque, and the flexibility of open or closed loop operation. This last bit isn't relevant since I believe SW also has encoders on the Steppers and is thus a closed loop system as we..<p class="citation">Quote
I am also told that the CGEM hand controller and firmware are more full-featured. Can someone confirm this?
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Having used both the CGEM HC software is more simple to operate. Less steps to get to a given task. But SynScan is catching up. I don't remember catalogwise which is more robust.

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Finally, the CGEM has the 8/3 periodic error problem: Its periodic error cannot be completely corrected by PEC because there is a periodicity in it that is longer than one revolution of the worm. That is noticed only by people who measure and analyze autoguider graphs. The AVX lacks it, which is one of the advantages of the AVX (a much lighter weight mount).
[/quote]
Correct save one part. The error does cause issues with long duration subexposures since you can't guide it out.

Clint Trotter

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #17 on: January 13, 2018, 04:34:58 AM »
I've been using the Atlas for about 11 years, a dozen times a month always in a different location for public outreach. It finally had a motherboard fail last summer, but Orion sold me a replacement and I had it in two days. I use a pretty heavy 10" Meade SCT and various Mallincam live video systems and it has been a joy. I even used EQMOD and Satellite Tracker and chased the Space Shuttle and ISS separately and together, and it never failed to put them in the center of the eyepiece.

I bought the GPS when it first came out, but it died in about two years and, frankly, it's useless for my purposes. It's just as easy to enter the Lat/Long/Time manually on setup. I tried the hand controller polar alignment routine a few times, but too often it took three iterations to get a good polar alignment and I can't afford the time on public events so now all I do is use the hand controller Polaris position and use the polar scope. A minute or two, and done. Since it is an older mount, the Polaris line is a bit far out as Polaris moves closer to the NCP, so I just fudge the Polaris location a bit inside the etched line, and I never have to relocate the target during the session. With the right set of stars IAW the manual, GOTO is precise enough that the target is visible in the video monitor. My only wish is that it had a more modern stellar alignment function. Actually, I've found that if I have a good polar alignment, all I need is a one-star alignment near the target and getting up and running is fast. It does have a three-star alignment but that is specifically to correct any cone error in the setup, and the first two stars must be on one side of the meridian and the third star on the opposite side. It also has a feature called Pointing Accuracy Enhancement, which allows the user to center on an object that was commanded for GOTO and it corrects for any errors in that segment of the sky. It divides the sky into over 80 zones, and PAE corrects for mechanical errors only in the vicinity of the target used. It doesn't improve the sky model, just the mount errors in a particular part of the sky so if you do a GOTO to The Ring and it's a bit off, you can center it and use PAE. From that point on, it will correct for errors in that AZ-EL part of the sky. Hours later, if you go back to The Ring it might be off again, but it will be dead on in the region of the earlier location of The Ring.

I've enjoyed it for over a decade.

musochoolsmee

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #18 on: January 13, 2018, 05:25:46 AM »
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The GPS module is only available with the EQ6 in Canada. The one supplied by Skywatcher USA does not include the module


That's unfortunate. The GPS is pretty expensive as an option, even up here if one needs a replacement.

What does the GPS do for you? The real-time clock in the CGEM only needs setting every few months. Go-to accuracy does not depend on precise location and time; it depends on showing the mount where some stars are. The CGEM remembers your latitude and longitude, which don't need to be reset unless you've traveled maybe a hundred miles.
If adjusted carefully for centering and then used with an app like Polar Scope Align Pro on the iPhone, the polar scope gets me to within about 15' of the true pole. That is good enough for everything except unguided long exposures. Celestron's all-star polar alignment routine gets me to within 10' on the first try and 5' if done twice. Drift method can do even better, of course. But there's nothing to fear from a slightly inaccurate polar alignment. The go-to computer compensates for it if you've done a three-star alignment, and (as I've shown in detail inAstrophotography for the Amateur) you're not going to have field rotation unless the error is much larger than any of the ones I've mentioned.
The purpose of the iPhone app is to tell you exactly how to orient the reticle so that Polaris is in the little circle. The constellations shown on Celestron's reticle are not to scale and don't match the sky very well.
I'm told the Sky-Watcher mount has a polar scope reticle like a clock face and the telescope's built-in computer tells you where to put Polaris on the clock. Is that right?

Mark Dominguez

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #19 on: January 13, 2018, 06:21:47 AM »
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<p class="citation">Quote
Finally, the CGEM has the 8/3 periodic error problem: Its periodic error cannot be completely corrected by PEC because there is a periodicity in it that is longer than one revolution of the worm. That is noticed only by people who measure and analyze autoguider graphs. The AVX lacks it, which is one of the advantages of the AVX (a much lighter weight mount).
Correct save one part. The error does cause issues with long duration subexposures since you can't guide it out.

Huh? Of course you can guide it out, can't you? Just as with any other periodic error, flexure, or refraction. What have I missed? It just can't be corrected in advance by PEC.
The excellent PEC of the AVX is one thing I enjoy about it. I make lots of 1-minute exposures with a 300-mm lens with no guiding corrections; could probably go substantially longer.

I have no inside information, but an educated guess might be that Celestron's next mount will have the brains of the AVX and the brawn of the CGEM. That is, a bigger AVX.

Coco Moten

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #20 on: January 13, 2018, 03:45:32 PM »
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What does the GPS do for you? ...

I'm told the Sky-Watcher mount has a polar scope reticle like a clock face and the telescope's built-in computer tells you where to put Polaris on the clock. Is that right?

The EQ6 GPS just automatically enters the date, time and location, same as the CGEM. Not needed as this can be done manually butits nice to have. I quite likeit and if it didn't come with one I'd probably buy one anyway even if it is way overpriced.

One note, the GPS for the EQ6 hand controller does not connect to a laptop due to a driver issue. So for EQMOD I have a different one.For EQMOD, any GPS that connects to a laptop using a virtual COM and NMEA message format should work.

The reticule on my EQ6 polar scope is the older Polaris circle and constellation pattern. I've also heard the new ones are a clock face. I think I'd like that type better since its hard to get the constellations to line up properly. In actual use, I don't evenbother trying.I just put Polaris on the big circle in the clock position given by the hand controller at power up. Doing it that way is not terribly accurate but its enough that I can go right to PHD for drift aligning if I want. (The polarscope isalignedthough, that helps a lot).

Guy Cleveland

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #21 on: January 14, 2018, 12:00:12 AM »
This is why I love CN. Hoping for a simple comparison between the two mounts, I instead was treated to a discussion of the idiosyncrasies of both mounts as well as an education. As a rank beginner my knowledge of things astronomical is minimal, but I'm learning, and discussions such as these delve way beyond the surface issues. I admit that some of the technology is beyond my understanding at this point, but it gives me a starting point from which to learn. Thanks to everyone.

I originally thought the CAVX would be a good mount for starters, but I'm still strong and would have no problem dealing with a heavier platform for my telescope. Obviously I have an eye toward AP, as photography has been an avocation of mine most of my life. The heavier CGEM or EQ6 would make an acceptable AP mount for planets and some DSOs. I'm leaning toward the Celestron mount, mostly because it is somewhat discounted if bundled with a SCT. I haven't had the luxury of a go-to mount yet, but I'm looking forward to it. 40 years ago my father bought an Edmund Scientific newt on a pier mount with an equatorial head. No drives, no slo-mo controls. We bought the accessory drive motors (crude beyond belief, even then) and we actually got the darn thing to track the moon and planets reasonably well for the technology of that junk. Go-to will be a treat.

chirafepes

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #22 on: January 17, 2018, 11:49:26 PM »
In your situation, that would be my preference too. Go for the heaviest mount that you will not have trouble setting up.

falkwinsliche

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #23 on: January 23, 2018, 05:08:28 PM »
I don't know if you said which telescope you're contemplating, but let me put in a good word for the 8-inch EdgeHD.

ebalared

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #24 on: January 23, 2018, 07:02:23 PM »
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Correct save one part. The error does cause issues with long duration subexposures since you can't guide it out.
Huh? Of course you can guide it out, can't you? Just as with any other periodic error, flexure, or refraction. What have I missed? It just can't be corrected in advance by PEC.
It can be guided out but not easily and it harangued PEC. And after looking into it again it seems the last firmware update fixed the problem. It happened to a subset of the mounts and not all of them and thus it was not a high priority.<p class="citation">QuoteThe excellent PEC of the AVX is one thing I enjoy about it. I make lots of 1-minute exposures with a 300-mm lens with no guiding corrections; could probably go substantially longer.I have no inside information, but an educated guess might be that Celestron's next mount will have the brains of the AVX and the brawn of the CGEM. That is, a bigger AVX.
Yes. I had two different AVX's at different times. They were great mounts. And on average would do 90 seconds unguided with good polar alignment. Some people get as high as 5 minutes with them. The longest I would get was about 60 seconds but that was because of LP saturation not the mount.

wordpuzzlesubc

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #25 on: January 25, 2018, 10:30:09 PM »
I would second the CGEM 8" EdgeHD SCT combination. It is a good platform for visual and AP at it's price. However be mindful of moving the CGEM head. Celestron recommends that you keep the clutches disengaged when you do and the bloody bugger will flip itself over while in your hands and bark your knuckles rather badly as well as pinch fingers.

senbevekek

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #26 on: January 28, 2018, 10:55:17 PM »
I would also strongly recommend that you get the TEMPest fans for the scope as it dramatically helps with cooling and keeping thermal equilibrium.

Coco Moten

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #27 on: January 31, 2018, 02:40:20 AM »
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I don't know if you said which telescope you're contemplating, but let me put in a good word for the 8-inch EdgeHD.


The 8" Edge HD is at the top of my list currently. After considering MCTs, 8" and 10" imaging newts (likely too heavy for a 40 lb. rated GEM) and refractors of more than 4" (rather costly in triplet or quad ED APOs), the Edge HD is looking very good. Even with photo gear it would be within the load range of the CGEM or EQ-6.

Do you have any comments regard Meade's 8" ACF SCTs?

Chris Jiles

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #28 on: January 31, 2018, 11:11:58 AM »
The Meade's are also very nice scopes. Though with one detail that puts the Edge's above them. The edges have the TEMPest fan retrofit. I cannot stress enough how valuable this is. Also the Meade's tend to be heavier. I like the color better on it though.  Optically they both do well though the Edge series is actually better because of the correction but on the flip side the Meade can get down to f/6.3 and even f/3.3 with the right focal reducer (with vignetting though) whereas the Edge only goes down to f/7

Scott Rogers

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Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #29 on: February 02, 2018, 08:03:30 PM »
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<p class="citation">dr.who, on 04 Feb 2016 - 8:31 PM, said:<a href="https://www.cloudynights.com/index.php?app=forums&amp;module=forums&amp;section=findpost&amp;pid=7036918" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="dr.who" data-cid="7036918" data-time="1454610666">
Correct save one part. The error does cause issues with long duration subexposures since you can't guide it out.

Huh? Of course you can guide it out, can't you? Just as with any other periodic error, flexure, or refraction. What have I missed? It just can't be corrected in advance by PEC.


It can be guided out but not easily and it harangued PEC. And after looking into it again it seems the last firmware update fixed the problem. It happened to a subset of the mounts and not all of them and thus it was not a high priority.


The 8/3 problem that I have heard about is mechanical in origin, due to a non-integer gear ratio, and can't be fixed or changed by firmware, but on the other hand is not any harder to guide out than any other periodic gear error. I don't think it's a serious problem, but it is a point on which the AVX is more advanced than the CGEM.