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CGEM-DX vs. Atlas

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#51 Wmacky

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Posted 01 November 2013 - 03:49 PM

As a person that "always seems to get the bad one" I appreciate these reports and warnings. Perhaps they will lead to less bad ones........

#52 ur7x

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Posted 01 November 2013 - 11:40 PM

So if I understand well short exposures help to bypass the 8/3 and cogging issues..and thats a way to come around the problem but I believe though that they can't substitute always longer exposures.
What if someone needs to go deeper on the picture and capture fainter objects that need exposures of at least 10 minutes...or for making it simple...what if someone has to do exposures of 20 or 30 minutes because uses Halpha;,O3 and S2 filters? Both issues inevitably will be present ( unless fixed) in every single exposure as I understand that the period of the Cgem Is less than 600 seconds..and ...if not ruined , every sub will be influenced in a way..:(...specially at longer focal lengths...


You answered your own question in your subsequent post. Most people live in places that yield background noise washout at ISO400 in 10-12 minutes. In my yard my CGEM will also produce perfectly repeatable 30 minute subs...of any part of the nights sky. Of course I can produce the same thing by taking a photo of a piece of gray card stock.

I have yet to find my mount to be my limitation. There are lots (too many really)of potential targets for my light polluted backyard. Someday I will solve this when I'm retired and I spend my nights on the top of a Hawaiian volcano taking photos.. Of course then I will discover the trade off of portability and set up and take down. My CGEM is already pretty heavy, the DX is even worse, its lunar lander tripod is a total beast.

The point is there is no such thing as a perfect mount. You will always be faced with a trade off... Discussion of 20 minute subs from urban locations on $1200 mounts is mostly moot. Its like trying to find a $20,000 vehicle that seats 5, goes 0-60 in 4.5seconds and get at least 35 mpg... of those 4 requirements... you can find lots of vehicles that will do 3... but pretty much none that do all 4... mounts are like that to.

Unguided my CGEM will cough out 90 second subs without issue.. guided I can easily produce 3-5 minute subs beyond that, at my viewing site, it is really diminishing returns.

My advice is simply buy the "strongest mount" that you can afford, move around, comfortable set up and take down (in the dark). Pick one with a large user base and a strong track record. And of course every mount will work better on solid pier. But Piers have their trade offs too.

I don't own an Atlas, never used one, so I can't comment on that mount. But if I were to buy a mount today. I would actually lean towards the Atlas... or wait for 6 months to see if Celestron adapts the AVX motors to the CGEM... if/when that happens that will be a very nice mount.

#53 orlyandico

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Posted 02 November 2013 - 01:37 AM

there's one reason to go 30 minutes from urban sites. narrowband.

i am curious as to (1) the keeper rate; (2) the focal length; (3) are you using a refractor or SCT; (4) are you using OAG - for Jason B.'s claim of "10 to 15 minutes all the time with a CGEM."

Over on TeamCelestron there was a guy imaging at 1600mm+ with an EDGE on a CGEM, and 20-minute plus exposures. But he had an AO unit.

#54 Mike X.

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Posted 02 November 2013 - 01:49 AM

I understand what you say but I never talked about taking photos from urban locations.i was talking about the mount in general. Personally I don't take photos from urban or suburban locations for example and if I would I would definitely use selective filters otherwise it has very little sense...at least for me.

A 1200 mount of course is not a mount I can pretend miracles from but that's no excuse for getting cogging issues or the so called 8/3 error...plus...3-5 minutes of autoguided shot is barely an achievement for any equatorial mount even a cg5 or a neq3.
What I do pretend from a mount though of 1200 € or $ is to work as intended...no miracles,no fantastic unguided shots or resolutions but at least work without cogging or extra PE induced by who knows what or 16/17 errors etc Etc etc.

Anyways long subs from urban locations with narrowband filters are the only way to do dso immaging for someone that cannot move and still wants to go deep..Otherwise light pollution will limit the session with shallow subs just as you mentioned .

It is not uncommon to do such kind of long subs with 1200 $ mounts.
Many people actually follow this path for urban locations by photographing in ha ..and actually with great results.

#55 Jason B

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Posted 02 November 2013 - 08:28 AM

i am curious as to (1) the keeper rate; (2) the focal length; (3) are you using a refractor or SCT; (4) are you using OAG - for Jason B.'s claim of "10 to 15 minutes all the time with a CGEM."


My "keeper rate" is in the 90 to 100% range if you don't include airplanes (I am between two international airports, Lansing and Grand Rapids, pain in the but).

I have 3 main imaging scopes (I have been experimenting with guidescope combos so bear with me):
An AT65 that I guide with a Orion SSAG/50mm Finder combo or it rides on the AT111.
An AT111 that I guide with the AT65 or the 50mm finder. I use the finder when traveling, the AT65 from home.
An AT8RC that I guide with the AT65 or the Miniguider. I don't travel with this set up. When I travel, I always take the AT111 or AT65. Mostly the 111 as I don't care to image from star parties and that is my favorite of my scopes for visual.
I tried using an AT10 F4 Newt but it was just too much for my mount. It seemed to guide ok as I got some good shots through it but the slewing seemed to really work my mount and I also found that being short and imaging with the newt was awkward.

I have gone up to 15 minutes with all 3 set ups. I don't do this on most targets as I shoot a lot of bright objects and being solely DSLR, these longer exposures really create noise issues with my DSLR. Here are a few example shots with the 1600mm AT8:

NGC891 with 10 minute subs
IC5146 with 10 min subs
Hickson 44 with 15 min subs

I am very meticulous about set up. I do my 2 + 4 and ASPA using the cross hairs on PHD with my SSAG through the main scope. I make sure it is perfectly balanced in DEC and barely east heavy in RA.

The only thing that I did to the mount (it was a display mount at NEAF) when I got it was adjust the play in DEC. I have not taken it apart and hypertuned or anything like that.

Look, I understand that not every mount coming out of Celestron or Orion or most of the other Chinese mount importers/makers will perform as well as mine. I am also sure that not every mount will perform as bad as yours or Stew57's did either. I just want to show that a serious imager can work with a CGEM. Did I get lucky? Maybe but so did two other members of my club that image as well so I know that it is more than just mine. Do I want to upgrade my mount someday? Heck yeah, at some point I will move up to the big boys like an AP, etc but it won't be because of a lack of performance from my CGEM. It will be when I have my own observatory and a large scope/camera set up to image my favorite objects, Planetary Nebula (and have a lot more money in the bank! :grin: ).

Everyone's mileage can and will vary of course.

Sorry for the long post!

#56 ur7x

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Posted 02 November 2013 - 08:52 AM

3-5 minutes of autoguided shot is barely an achievement for any equatorial mount even a cg5 or a neq3.


I completely agree! and that was exactly what I was trying to say. For just about anyone, living in (or near) a town of 100K or more (which is about 90% of us) you will have positive results with either mount. (or even a AVX, CG5, EQ3, etc as long as your OTA isn't too large or too heavy).

Back to another car analogy, where I live, my morning commute is about 30 minutes...I do it in a 5 year old Lexus Sport Sedan... that commute would be pretty much the same duration in a 1969 GTO, a 1990 Corolla, or a 2013 DB9. The car is not the limiting factor in the duration of the commute, congestion, road conditions, and traffic fines play a larger role then how fast (or slow) the car you buy is. Of course all four of those cars offer a completely different ownership cost and experience.

For most of us any decent mount that can hold the scope steady and can track the night's sky will produce photos like the one I posted a page or two ago.

There are lots of reasons to pick the Atlas, there are lots of reasons to pick the DX. Both can and do work. For most of us, due to other limitations, neither will work better than the other.

#57 Mike X.

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Posted 02 November 2013 - 12:16 PM

The point is, the 8/3 issue and the cogging prevents (at least from what i read both here and on the yahoogroups) the CGEM to act as a decent mount for DSO photogaphy--or is a cause of frustration for many users.So if not all many CGEMs do present this issues..otherwise i don't understand all the fuzz around these issues...
Plus we have to keep in mind also expectations. From person to person may be different regarding the mount and it's performance.
Of course noone will see this issue in visual or hi res photography and of course many friends that do low focal lenght photography might not even notice the issue...but still a problem is a problem and the statistics of how many use the mount in a certain way or not won't change the fact that the problem exists..and...for 1200$ i just cant't accept to get a defective product since there are alternatives...because even if it's not a state of the art mount...1200$ is still good money for many of us..if not a lot...not talking about the difference of having fun shooting the stars instead of "having fun" trying to "solve" a congenital issue of the mount :tonofbricks:

I can accept the fact that i have to tinker to improve performance, it is perfectly normal in ths range of mounts..but fix an issue that comes from the production line?... :question: :help:

PS:I read loads of posts about the hit or miss probability to get a mount really affected by these issues...and that's what made me change my mind..Not because there aren't CGEM's capable of delivering excellent results but because , at least from what i understood it is like playing Russian roulette to get a lemon or not.

I know i'm blunt guys, please don't take it bad , it's only my opinion and nothing more.

#58 ur7x

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Posted 02 November 2013 - 02:19 PM

Let me help clarify and explain the fuzz.

First off Celestron Software Engineers have resolved the cogging problem, a software patch for the subset of CGEMs that exhibit this problem has been available for a few months now. Of course cogging was only an issue while guiding long exposures on the Dec axis and again short exposures and a bang on polar align will solve that issue without any patches or tinkering. Bang on polar alignment is not tinkering for AP... it is kinda a prerequisite.

Next, the 8/3 problem basically makes the PEC system, dare I say it, useless. In this case we see lots of evidence that just about any decent guide scope and camera can easily deal with this problem to the limits of most sites seeing conditions. Again, it is hard to describe bolting on a guide scope/camera, turning off PEC and letting it all do its thing as tinkering.

Would it all work better if the PEC system was more effective? Sure... Is there ample evidence that the CGEM can take pretty nice Deep Sky photos? Absolutely. Is it possible to take shots of even mag 20 objects using stacked 90 second subs... Of course. We see examples of photos like that in this thread.

You are starting to lose me, I'm not sure what you are trying to express. Would the CGEM be better if it had the AVX motors and gears? Again, absolutely! Does it work fine as is today? Yup. Is it better than an Atlas? No... Is the Atlas better? debatable.

#59 Mike X.

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Posted 02 November 2013 - 03:31 PM

Sorry if i lose you , that's not my intention of course.

It happens to know how important polar alingment is as i do DSO photography myself for several years now and of course that is not tinkering.
Tinkering is to have to "hypertune","overtune","supertune" a modify or enchance a mount to perform better than it does right out of the box..just for making things clear.

What i mean is that a mount with a problem coming out of the factory (and that has not been solved up to ...afew weeks-motnhs are you say with a software release) for the cogging issue (they can't do much for the 8/3 issue with software unfortunatelly) is a no deal for me.

Now if the CGEM had no such issues (it came out in 2009 if i remember well) i would no doubt get one instead of an Atlas and not because one is better than the other..but because i like it more.But it did had and it stil does have the 8/3 so..since there is the option to avoid it...i chose to void it.It's that simple.
One less factor that introduces PE to the system is good enough for me to chose that mount over another.

What i find debatable is the equivalence of short exposures VS long exposures for the same amount of integration.
If that was true..noone would bother to guide or even get an expensive mount..everyone would go with 1 or 2 second shots..thousands of them so the noise would be so low they would not even need to pass any denoise filter or even bother to shoot darks.

So for coming in topic at this point where the CGEM and the CGEM DX still have the igarshi motors, still present the 8/3s issue..etc etc..to me are a step down over their counterparts.
They do have the potential to deliver identical results, they do have the potential to be better as a whole..but at least for me..where tracking counts more over esthetics and electronics...they are not.

#60 ur7x

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Posted 02 November 2013 - 06:17 PM

Everyone would go with 1 or 2 second shots..thousands of them so the noise would be so low they would not even need to pass any denoise filter or even bother to shoot darks.


That is not as much of a strawman as you intended. Depending on how bright the object is the technique that you scoff at is actually preferred for taking shots of objects like Jupiter, Saturn, Mars, etc. Thousands of short exposure shots is exactly how a Webcam cam produce stunning images of brighter objects.

Just as sky glow will actually diminish results after 10 minutes (as you posted) Ultra short shots have the same problem at the other end of the spectrum depending on dim you want to go. Of course you and I both know that most of the Messier objects can be easily capture with 60 second subs... Some of them will come out nicely with one 60 snap. I have been doing deep sky photography since the mid 80's I have struggled with 35mm slides, cold cameras and uber long focal length guide scopes as I stare into illuminated eyepieces nudging the mount with frozen hands on slow-mo buttons.

As you say, to be blunt, if you want to have a discussion of deep sky techniques, I'm game, if you only want to throw out extreme strawmen arguments then I'll bow out of this.

#61 Mike X.

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Posted 02 November 2013 - 08:32 PM

i find noting extreme by taking a postition ,with reason towards a mount choice urx7x.Plus that remains my personal opinion only and it is always open for debate. I was blunt regarding the mount and nothing else.I wouldn't even dream to be blunt towards a fellow astrophotographer or observer.
I would be and I am always happy to discuss and exchange opinions regarding astrophotography techniques but this would be by far off topic on this thread.
I find the same extreme to put on the same basis the needs of everyone that buys a mount of 1200 $ and say ..." Hey ...after all 90% of us live in urban locations..it's alright even if the mount is not working properly...I will find another way around by reducing my exposures,avoiding guiding in dec ,changing my targets or even accepting the fact that that the sky has only 110 objects and a few solar system objects....

I don't throw out extreme arguments and I'm always ready to accept I'm wrong but isn't it extreme too to keep denying the most evident thing?
The Cgem had design flaws ,some got probably fixed by the beta patch ( i guess the cogging) released recently and some still have to be solved ( the 8/3 error).
Flaws that for some are less important than others.
After all this is a forum,we are here to discuss we have nothing to divide.

Here is an example with my mount if it can help make underhand what I try to say regarding the mount.

My azeq6 has a power leakage when powered with a ac/dc adapter.It still works fine , tracks perfectly and points like a charm..but hey..it shouldn't do that! Maybe I am doing something wrong, maybe the mount has an issue.With some friends we tested several mounts, even with the dealer here in Rome, all presented the same issue....
If we power up the mount with a battery ...of course there is no leakage...but that doesn't means is a solution or that the mount doesn't has an issue ..since it is designed to work even if powered by an adapter.It is only a remedy, just like reducing the exposures or keeping guiding in dec to a minimum or zero.

I don't know maybe it is my fault that I can't explain myself ,it is evident that my English is poor but please understand that I don't seek any kind of argument.iT has no sense to argue over a piece of equipment .

PS .and of course I would love to discuss with you about astrophotography techniques and exchange opinions whenever and occasion will be presented ;)

#62 Moromete

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Posted 03 November 2013 - 12:56 AM

Mike, actually it seems to me there is nothing wrong with your mount regarding the power leakeage because at the bottom of page 17 of AZ-EQ6 manual (not Synscan manual) is written:
- " Do not use an un-regulated AC-to-DC adapter. When choosing an AC adapter, it is recommended to use a switching power supply with 15V output voltage and at least 3A output current." :D

#63 Mike X.

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Posted 03 November 2013 - 04:50 AM

Hello Moromete i think too this is the case at the end.I am also waiting confirm from the importer just to be sure,I believe in a few days to have it,and of course I will let you know;)

#64 ScenicCityPhoto

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Posted 06 November 2013 - 10:44 AM

So I had a unique opportunity to use the Atlas at a friend of an acquaintance's house, I know right?!?. And the best part? I also got to try out the CGEM a week ago as well at another persons house (read- see it guide, operate, take an image at 3min).

Unfortunately, I came away like the exposure I took on the CGEM better. Admittedly, there was better seeing with the CGEM, but the single exposure was better in detail (same scope on both). The setup was way faster and both persons had to setup from scratch. I think the CGEM user was definitely more tech friendly, but total time to imaging was around 30-45min I'd guess. The Atlas user had stated he was having trouble with the alignment and that it was tricky for him as he could not see the Northern star, save for through the trees which made me wonder if he even aligned on Polaris and maybe not another star. It took around an hour and a half to get in tracking and guiding and he had software issues again because of Windows 7 wanted to update. lol. Both users told me they have imaged for 3-5 minutes, but the Atlas user said he usually just did around 1-2 minutes and stacked them. He showed me some of his work, great stuff.

I walked away feeling the CGEM was the mount for me once again. Even though I didn't want to even consider it with all the issues. So I called my buddy who manages Best Buy and can order the CGEM DX and inquired as to return policy, should there be an issue and was told it would be covered by the "marketplace vendor" they use for 14 days. Another awesome thing is that it's on sale. The DX is $1699 on amazon & best buy, that's $500 cheaper than it was last week and $500 cheaper than the Atlas. :/ Oh man, not making it easy.

So now I'm wrestling with the issue again, despite all of this good info on the issues, I'm wondering if I might hit the lottery or reap the whirlwind.

Man, I'm torn. I don't need convincing, I'm going to make up my own mind. I appreciate all of your help in my decision and I feel at this point, I'm making a very informed decision either way. Looks like I'll just be taking my chances.

One question I do have is, WHERE DO YOU GUYS get your gear? Who is the best with customer service and help when there is an issue?

In the mean time, here is my SWAN SONG from my astrotrac and DSLR. She was a gateway drug for me. I feel I have taken it to the VERY limit of what it can do!

Posted Image


#65 orlyandico

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Posted 06 November 2013 - 11:13 AM

The atlas probably had less good results due to poorer polar alignment... That said the newest synscan firmware also has an all star polar align routine.

If I were you, wait till Christmas. Who knows, a CGEM AVX might be announced and all the CGEMs will lose half their value.

#66 dragonslayer1

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Posted 06 November 2013 - 12:23 PM

I have another input.. I just bought a CGEM and love it,,,, I saw them on sale and waited uggghhhhh, missed the sale and bought full price,,,,, a week or two later they are on sale LOL,,, "get while the gettings good",
Kasey

#67 DaveJ

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Posted 06 November 2013 - 03:08 PM

The DX is $1699 on amazon & best buy, that's $500 cheaper than it was last week and $500 cheaper than the Atlas...
One question I do have is, WHERE DO YOU GUYS get your gear? Who is the best with customer service and help when there is an issue?


Here's where I got mine: Link. I've always had great service from Astronomics. Same price, free shipping and a full two year warranty.

#68 ScenicCityPhoto

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Posted 27 December 2013 - 01:54 PM

Well guys, I'm back.

I always like to come back and give info on what I've discovered for folks who actually use the "Search" feature.

So, two months now with a used CGEM DX and I couldn't be happier.

I'm imaging for 3 minutes at 550mm with a Skywatcher 100mm ESPRIT. I bought a used setup with a broken focuser and while I'm very happy with optics of my 100mm ESPRIT, the bent focuser leaves much to be desired. After the new moon in January, it's going to moonlight to be customized. It is serviceable now, but a pain.

The CGEM DX I got was one with the newer electronics and could track for 3 minutes unguided with NO ISSUE. The guy I got it from was convinced it had a terrible 8/3 issue, but I've seen no issue with it. I think he had too much weight on it with a giant reflector and a refractor. What I paid was ridiculous so I jumped on it. I feel very lucky as I did take a chance, but I also believe had I not been a fairly "tech-oriented person" I would have been lost fixing the few things wrong with my used setup. The tripod had taken a spill and the previous owner had managed to slew the telescope so far it snapped the power connector from the board damaging the coupler. Easy fixes with the right parts. The motors were LOUD and I was worried one was about to fail as it sounds precarious, but it's held out like a champ.

Anyway, here's my latest photo from the Horse Head & Flame Nebula.

41 lights & 41 darks @ 3 minutes each, ISO 800 on a Hap Griffin modified 60d. Around 2 hours total integration. Taken with a CGEM Mount & a Skywatcher 100mm Esprit. Edited in Deep Sky Stacker, & PS.

Posted Image

And my personal review of the CGEM DX:

PROS-
- GREAT software and support
- Controlling with iPad & Surface tablets are awesome!
- Easy setup
- parts readily available
- Easily handles my 20lb scope
- Provided you get a good one, it's relatively simple to get it going

CONS
- Saddle is suspect- I upgraded to ADM saddle
- Provided weight is too freaking heavy. Need two smaller weights to balance correctly
- Doesn't come with a polar scope and it really should
- Hand controller cord is way short
- Chance of getting one with BAD 8/3 error as described in this thread

#69 scopenitout

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Posted 27 December 2013 - 06:03 PM

Cons?
-Never had any issues with the saddle other than wishing it was "Dual V & D". And yes, an ADM could take care of that.
-Heavy for sure. And it's very stable. I'm 64 and can handle it just fine. Bought an extra CW for the C-11 Edge and full load of AP gear it has to carry.
-Polar scope? A waste of money when you can use ASPA and your camera for excellent PA's.
-The short HC cord is a damn nuisance. "Scope Stuff" makes an inexpensive extension. A must.
-8/3 error non-existent in my example and I suspect in the majority of the thousands made.






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