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Equipment Discussions >> Mounts

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ScenicCityPhoto
member


Reged: 10/17/13

Loc: Chattanooga Tennessee
Re: CGEM-DX vs. Atlas new [Re: Stew57]
      #6164165 - 10/29/13 09:01 AM

Is that even after you've applied the "fix" Mark?

My whole reason for this mounting a AP. As my FL is 550mm with a little bit added by my crop sensor, I'm VERY concerned as to what is acceptable and what is not.


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Jason B
Proud father of 5!!
*****

Reged: 06/21/04

Loc: Mid-Michigan
Re: CGEM-DX vs. Atlas new [Re: Stew57]
      #6164166 - 10/29/13 09:01 AM

Having extensively used both an Atlas and a CGEM, I would take the CGEM.

The Atlas worked great, I just didn't care for the hand control. It guided well, was relatively easy to learn the controller and is reliable.

The CGEM/Nexstar system is just better for me. I get good guiding up to 1600mm with my AT8RC (15min subs are my longest) and have had none of the issues you repeatedly read about here. The Polar Alignment routine works great for me as well and allows me to quickly set up with my limited time available this time of the year (if it actually clears here in Michigan!). In the astrphoto group in my club, 2 other CGEM's have worked just as good and one of them has done up to 5 min guided exposures at 2000mm with good results (C8). All 3 of our mounts are good, if not great, imaging mounts for what we use them for. All are 3 years old or newer.

There are good and bad stories for every mount in this price range so you just have to go with the features that are best for you. YMMV as has been said many times.


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM-DX vs. Atlas new [Re: ScenicCityPhoto]
      #6165214 - 10/29/13 07:30 PM

Here are 4 2 min shots (one complete worm rotation) unguided, C11 F10.
http://s906.photobucket.com/user/mstew57/library/CGEM/CGEM%20tests?sort=3&...

At <600mm FL and minimal weight you will get good results. I would think you will still have to guide though, but you could use a miniguider or finder turned guidescope. But then again your mount may be better. The old YMMV still applies.


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warren2256
member


Reged: 10/07/13

Loc: Rosenberg Tx
Re: CGEM-DX vs. Atlas new [Re: Stew57]
      #6165413 - 10/29/13 09:39 PM

ok newbie question but what exactly is the 8/3 cogging mean? i just got a 800 hd cgem version not dx and you all have me worried... not to sure what yall mean by it

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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: CGEM-DX vs. Atlas new [Re: warren2256]
      #6165425 - 10/29/13 09:45 PM

Warren, 8/3 and cogging are different.

8/3 is a periodic error with an irrational period (2.667X or 8/3 times faster than the fundamental) that cannot be removed by periodic error correction. This 8/3 error is due to the gearbox of the motor in both the CGEM and DX.

For "most" CGEMs according to Celestron the 8/3 is of small magnitude, under 8 arc-seconds peak to peak, but on some - like mine and Mark's - it was huge (over 25" peak-to-peak).

The cogging is the tendency of the declination motor to resist small movements (to "cog" as if it has detents) which gives problems when guiding in declination. Supposedly fixed now with new firmware, I have no way to check as I sold my CGEM.


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petemumbower
Carpal Tunnel


Reged: 07/12/09

Loc: West Michigan
Re: CGEM-DX vs. Atlas new [Re: orlyandico]
      #6165435 - 10/29/13 09:53 PM

Tough thing here is you seem to either get a decent CGEM or a bad one. Though the there seems to be more "Good" vs "Bad". I have worked the TeamCelestron.com site beta testing the firmware to fix the cogging and I must say it is a non issue now for me. Though the 8/3 is still there in my mount.

I seem to have a decent one that is guideable. Below is an image of M1 taken at f/10 with my c9.25 (2350mm) with 2 and 4 min subexposures.



Edited by petemumbower (10/29/13 09:53 PM)


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: CGEM-DX vs. Atlas new [Re: petemumbower]
      #6165460 - 10/29/13 10:03 PM

of course.. squeaky wheel and all that. You'll always hear from the guys like Mark and myself who got burned. So our experiences probably don't represent a majority of CGEM owners. But the possibility is there.

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petemumbower
Carpal Tunnel


Reged: 07/12/09

Loc: West Michigan
Re: CGEM-DX vs. Atlas new [Re: orlyandico]
      #6165479 - 10/29/13 10:12 PM

I agree and it is good to know about the good/bad for a mount in this price range before getting one. Good for entry level AP and even intermediate-advance if you are dedicated to working with the mount and working within its limits. That being said, I am working toward getting a AP900/1200 class mount to take my work to the next level.

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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM-DX vs. Atlas new [Re: petemumbower]
      #6165573 - 10/30/13 12:22 AM

hHello,I've been reading the entire thread, which i find really interesting but at this point i arrived at a question that came to me naturally and it is the same i asked myself 6 months ago:

If someone wants to do photography (entry or intermediate level)..then..why get a mount that has both an uncorrectable error (probably guidable,probably not,and if if so...the guider should work both against PE and the 8/3 error which is not fantastic actually)..and a possible cogging issue?
Just for the Nexstar software?(which i do like alot due to my previous mount a CG5..)

Isn't it better to eliminate at least from the begining 2 factors that will eventually make things more difficult in photography? (8/3 and cogging)?
I mean let's face it..both the Atlas and the CGEM series are not Astrophysics mounts (sorry if i'm blunt)..so..why complicate things with 2 extra errors plus the usual PE,wind,seeing etc someone has to deal during the night?

I put these things to the scale and..at least for me it went towards teh Atlas/AZEQ6 even if Nexstar can be more user friendly.

I haven't chosen the Atlas way immediatelly i must say..i have been waiting for around 2 years to see how the situation will evolve with the CGEMs because i like them but..to me it seems the situation is not changed.
This is just my thought of course nothing more.


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM-DX vs. Atlas new [Re: Mike X.]
      #6165588 - 10/30/13 12:35 AM

The cogging is to be a non issue very shortly. They have emailed me a few times stating that a fix for the 8?3 error is in the works, but I have not heard anything recently. The pointing accuracy, ASPA, and the HC software in general is hard to beat. Of course the Atlas has an ASPA type routine now and EQmod.

Personally I am counting pennies trying to go towards an EQ8 class mount.


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: CGEM-DX vs. Atlas new [Re: Stew57]
      #6165607 - 10/30/13 12:46 AM

this is what i keep saying.. i agree with Mike X.

it's good that the cogging is getting fixed.. after how many years?

i don't think the 8/3 can be fixed in software. it will require a gearbox swap. So unless the gearbox swap is free for existing or new CGEM owners, that would be an extra cost.

the Atlas simply has less that can go wrong with it - stepper motor drive, so dead simple. The gearbox has two gears (!) and a low reduction, so there are less gearbox induced errors.

that said the EQ8 with its no-gearbox design is taking simplicity to the extreme. and why not? no gearbox means no gearbox periodic error. because the only way to get rid of gearbox errors is to make or use an expensive gearbox. as I understand it, Astro-Physics doesn't even use a stock Maxon gearbox, they make their own.. (and Maxon gearboxes are pretty high-end)


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warren2256
member


Reged: 10/07/13

Loc: Rosenberg Tx
Re: CGEM-DX vs. Atlas new [Re: orlyandico]
      #6167215 - 10/30/13 08:19 PM

well im barley getting stated into AP havent noticed yet... but thank you for the response, definitley going to keep an eye out!

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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM-DX vs. Atlas new [Re: warren2256]
      #6167239 - 10/30/13 08:29 PM

Indeed the EQ8 uses belts just like the AZEQ6 if i'm not wrong..which i'm really really happy so far both from a tracking and goto point of view.

Edited by Mike X. (10/30/13 10:04 PM)


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WesC
Carpal Tunnel
*****

Reged: 02/06/13

Loc: La Crescenta, CA
Re: CGEM-DX vs. Atlas new [Re: Mike X.]
      #6167335 - 10/30/13 09:18 PM

The only reason I got a CGEM is because it came with my C11 Edge for an extra hundred bucks!

But honestly, for visual it has been a great mount.


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tim57064
Pooh-Bah
*****

Reged: 08/23/12

Loc: Southeast South Dakota,USA
Re: CGEM-DX vs. Atlas new [Re: WesC]
      #6167375 - 10/30/13 09:40 PM

Has anyone ever used a 10"SCT on a cgem permanently mounted on an OBS concrete pier for AP? Or an Atlas?

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ur7x
professor emeritus


Reged: 01/08/12

Re: CGEM-DX vs. Atlas new [Re: tim57064]
      #6167390 - 10/30/13 09:49 PM Attachment (36 downloads)

I have a 9.25" on my pier mounted CGEM. Works great.
Could probably get away with a 11"

I guess a photo might help.

M51. 3x 90 second unguided F6.5 reducer Stock Canon T3i

My pier is a thick steel 60+ pound monster that is itself a foot underground and is bolted to a 5' deep "blob" of concrete that is about 1/2 of a yard big... 3 LARGE wheelbarrows full of concrete (at least 1000 pounds of rocks and and cement).

You can bang the pier with your hand and the scope barely giggles visually.. Having the base literally rock solid makes a huge difference.


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Raginar
Postmaster
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: CGEM-DX vs. Atlas new [Re: tim57064]
      #6167391 - 10/30/13 09:50 PM

Tim, I had your scope. It was mounted on my wooden pier (6x6, 3' deep) on a CGEM. It wasn't good for imaging. The CGEM could 'barely' tolerate it. But with the right balance it was doable for visual. For imaging? No way.

My 12" is currently visual only. The 6x6 just isn't good enough. I'm probably gonna rip it out next summer and sink a real pier.


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tim57064
Pooh-Bah
*****

Reged: 08/23/12

Loc: Southeast South Dakota,USA
Re: CGEM-DX vs. Atlas new [Re: Raginar]
      #6167449 - 10/30/13 10:33 PM

Thanks for the info Chris.Guess I was hoping the CGEM would be doable at AP with the 10. Gonna continue keep an eye out for the Atlas EQG I guess.

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: CGEM-DX vs. Atlas new [Re: ScenicCityPhoto]
      #6167531 - 10/30/13 11:29 PM

The CGEM and Atlas heads have virtually identical capacity. The DX gains it's extra payload capability courtesy of one of the heaviest tripods in the world. A tripod made for a 100# mount head but used for a 40# mount head instead. If you're pier mounting it they are 6 of one, half dozen the other. Particularly if you retrofit the Atlas with the larger counterweight shaft. If you need the extra capacity of the DX and plan on using the native tripod, then it is really your only choice in this general price range (assuming GOTO). The standard CGEM and Atlas are closer, with identical capacities.

The Atlas supports EQMOD. The CGEM twins do not. Nexstar firmware is much better than Synscan though.

If you don't need GOTO, the standard non-Gemini G11 is a similarly priced, better made mount with much higher capacity. Just another option.

- Jim


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Moromete
professor emeritus


Reged: 02/15/12

Loc: Romania
Re: CGEM-DX vs. Atlas new [Re: jrbarnett]
      #6167642 - 10/31/13 01:08 AM

AZ-EQ6/ATLAS PRO AZ is a viable option too and it's better than EQ6/Atlas. This dual mount coppied Losmandy G11 slip clutch system for both axes.
In my very short experience with Synscan HC and much longer with Nexstar HC, I can tell you that AZ-EQ6 can reach the pointing accuracy of a CG5GT(after 2+2 star alignment) or maybe exceed it a little ONLY if you use the right mix of 3 alignment stars as I have seen so far. With the right mix of 3 stars AZEQ6 will any dso in the FOV of a Mallincam or eyepiece at ~100x with a C11.

Even so I still find Nexstar easier to align than Synscan because with Nexstar I have very good gotos without being too carefull which stars to pick as long as I do 2+2 star alignment. With Synscan it seems you have to be very carefull what stars to pick for alignment and avoid Vega as 3rd star for correcting cone error.
So yes, Nexstar has a more advanced sky modelling which gives very good gotos easier. Also Nexstar has unique functions like Goto Precision, reduced speed of crowling text on display for winter nights, much more alignment stars for 2nd and 3rd star, probably still better ASPA, etc.
I see Nexstar as a Mercedes and Synscan as VW somehow.

Oh, AZEQ6 is much more quiter a max speed when slewing than a CG5GT and probably a CGEM too.

For anybody wondering the dual encoders of AZEQ6 really work well enough even if you declutch on both axes. The gotos will be just a little worse but still good: e.g. suppose you have a dso in the middle of the eyepiece at 100x after a 3 star alignment, than you decluth both Ra and Dec axes and move the mount on another part of the sky, and finally you engage the clutches again and do a goto to the same or another dso. The dso will land somewhere in the FOV at 100x as I have seen.

In plus you can use AZ-EQ6 in AZ mode with 1 or 2 scopes when doing visual work only and still have goto capability which is unique in this class of mount.

One point to note: in Europe AZ-EQ6 costs the same or less than the standard CGEM, not DX.


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