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CGEM vs CGEM DX

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#51 dragonslayer1

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Posted 19 October 2013 - 08:41 AM

PS now am using C9.25 on CG-5; this is to be travel mount,
Kasey

#52 Stew57

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Posted 19 October 2013 - 09:10 AM

It is true that in the past those doing astrovideo had lower expectations. It seems that they are becoming more demanding. The chip does not care if it is in a dedicated ccd camera or a video camera. The error is the same.

#53 Raginar

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Posted 19 October 2013 - 09:30 AM

The G11 is just fine. It probably has as many issues from people tinkering with it as legitimate problems. Somewhat similar to a CGEM. The new G11s certainly don't have the work gear issues like the old ones. There was a bad batch in 2012.

#54 rmollise

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Posted 19 October 2013 - 12:21 PM

It is true that in the past those doing astrovideo had lower expectations. It seems that they are becoming more demanding. The chip does not care if it is in a dedicated ccd camera or a video camera. The error is the same.


Most video users are still not doing long exposures, however--it's not necessary--and most CGEM users have had better luck with their mounts than you have. I'm sorry you have had trouble, but, frankly, you experience is not typical. ;)

#55 Stew57

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Posted 19 October 2013 - 02:29 PM

The servos in the CGEM and DX are pulse driven. They are operated like steppers that use encoders rather than count steps. The advantage you list for servos does not exist for the CGEM\DX.

#56 dragonslayer1

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Posted 19 October 2013 - 02:40 PM

OK, so trying to see if I understand this right, if they were "servo" driven, there would not be a pulse but more like a potentiometer or reostat controlling a steady source of voltage or current?? The "encoders" would have to be changed to run them like servos rather thanpulse driven?? Am I even close to getting it??? :question:, Kasey

#57 Stew57

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Posted 19 October 2013 - 04:08 PM

If you are polar aligned only the RA would be driven. There would be a constant current only varied as the encoder relied being ahead or behind the correct position. The servos in the CGEM are given pulses of curret that drive the RA. There is nothing wrong being pulse driven. Servos being better than high resolution steppers is a red herring in my opinion.

#58 orlyandico

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Posted 19 October 2013 - 10:43 PM

No, no, no.. all servo motors are driven using PWM (pulse wide modulation). Nobody drives servos with constant current, it would be too inefficient.

Servos still have advantages over steppers - more torque at low speeds (no need to micro-step) and a larger dynamic range, i.e. they can run at both low speeds and high speeds very well. With steppers you have to decide whether you want very fine low-speed performance (in which case the maximum speed is compromised).

That said, a not-so-good servo implementation results in... cogging.

Kasey, you are over-analyzing this. As Rod has said, there isn't much difference between all the mounts in this class. And your concern about the Atlas having 6lb less capacity? that's irrelevant. The weight ratings Celestron and Orion throw out are optimistic anyway. I would go with the Atlas, for reasons already previously stated.

#59 A. Viegas

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Posted 20 October 2013 - 07:23 AM

Kasey-

So early this morning I tried using my C8 on the CGEM with my Mallincam Extreme and I did not guide. Conclusion is you can probably get 60s - 90s without too much trouble if you bother to decently polar align. My PEC training apparently sucks because it messed up a few of the pics, so maybe if you are not a total doob like me and you can figure out PEC maybe that gets to about 2mins?

For my test run I ran the following:

CGEM with 1 17# and 1 11# counterweight
C8 with C80ED refractor piggybacked + 50mm finder +MCX and Orion SSPIAG guider. So probably 27 # I am guessing total weight.

There was a full moon and I did not use any filters. For the Mallincam I used ONLY the MFR3 rear element which according to my astro-aid APP and Astrometry.net is basically F8 so ~1600mm FL - a decent test I think.

Ok here are the images. Easy one first

M42 - MCX in CCD Mode (NO AGC) - C8 @ F8 --35 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28474&password=&sort=7&thecat=500[/image]


M42 - MCX in CCD Mode (NO AGC) - C8 @ F8 --50 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28473&password=&sort=7&thecat=500[/image]

NGC1514 - MCX in CCD Mode (NO AGC) - C8 @ F8 --90 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28472&password=&sort=7&thecat=500[/image]

-Note this last one was close to the moon and i found out later a leaf had fallen on the corrector making that mark in the upper right corner.

As you can see at 90 seconds I was starting to get trailing.

--Hope this helps

Al

#60 Stew57

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Posted 20 October 2013 - 08:17 AM

I stand corrected. Thanks
There is one advantage to a stepper often over looked. When overloaded a stepper will just sit and try and step with no ill efects. The servor will draw more current until something spills it's magic blue smoke, unless there is some type of overload protection built in the circuit.

#61 Stew57

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Posted 20 October 2013 - 08:39 AM

I stand corrected. Thanks
There is one advantage to a stepper often over looked. When overloaded a stepper will just sit and try and step with no ill efects. The servor will draw more current until something spills it's magic blue smoke.

#62 rmollise

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Posted 20 October 2013 - 09:19 AM

Kasey-

So early this morning I tried using my C8 on the CGEM with my Mallincam Extreme and I did not guide. Conclusion is you can probably get 60s - 90s without too much trouble if you bother to decently polar align.


Let me add that 60 - 90-seconds with a very sensitive Mallincam is about the maximum exposure for most peoples' skies. My most used exposure with the Mallincam Xtreme is 14-seconds, and my max is usually 30, and this is from fairly dark sites including the Chiefland Astronomy Village...

Also, most video users are not obsessed with pretty pictures. We want to go deep and see lots of detail, and off-round stars once in a while are simply not a big deal for most of us.

Take your pick, CGEM or Atlas; both will do just fine. You may find the Celestron's hand control and alignment system easier to use, however. ;)

#63 Mike X.

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Posted 20 October 2013 - 09:28 AM

I stand corrected. Thanks
There is one advantage to a stepper often over looked. When overloaded a stepper will just sit and try and step with no ill efects. The servor will draw more current until something spills it's magic blue smoke.


Or a plastic gear which i believe the celestron motors actually have.At least the cg5 ones do.
So when it comes to a situation like this, if we are lucky enough the gear will break before the motor rests in peace.

#64 dragonslayer1

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Posted 20 October 2013 - 09:34 AM

Hey Al,
Thank you very very very much for the time and effort you put forth in doing that. I was wondering if it could be slightly off on polar align?? The trails or egg shapes look pretty consistent (have no clue what cogging or 8/3 error would look like :question:),, and just a heads up.. I have a question to Team Celestron on the cogging and 8/3. Derick answered the cogging and says they have a firmware fix ready to roll out to fix it. The 8/3 no answer yet but from all I gather not too sure that will be addressed in the near future as probably will require motor/gear change...
I don't think the 8/3 can be fixed with PEC from what I can gather from people above my pay grade. You might want to check that answer in T/C I posted on cogging tho and get the firmware fix.... One thing is for sure, if they do address the 8/3 their will be a 99.999999% chance there will be an upgrade for older mounts :jump:,,, Thank you so much again Al, is much appreciated,
Kasey

#65 dragonslayer1

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Posted 20 October 2013 - 09:38 AM

Thank you Mark,
I think with your patience I am finally able to wrap my head around the stepper/servo issue.. That really makes sense now :bow:. Thank you, Kasey

#66 dragonslayer1

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Posted 22 October 2013 - 02:35 PM

A FYI from Derik on CGEM vs CGEM-DX motors, electronics, gears , etc.
""It used to be that the CGEM and the CGEM had different electronics. But as of some time last year, all CGEM's have the updated electronics. So nowadays, the biggest differences is the Tripod, and the longer clutch knobs.""'
Kasey

#67 DaveJ

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Posted 22 October 2013 - 02:44 PM

A FYI from Derik on CGEM vs CGEM-DX motors, electronics, gears , etc.
"It used to be that the CGEM and the CGEM had different electronics. But as of some time last year, all CGEM's have the updated electronics. So nowadays, the biggest differences is the Tripod, and the longer clutch knobs."


Plus a much longer, thicker & heavier counterweight shaft (1.25" diameter vs what, 3/4" or 7/8"?) and heavier counterweights.

#68 dragonslayer1

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Posted 22 October 2013 - 03:10 PM

Yes and now trying to decide on DX or just CGEM???? Right now using a C 9.25 & have Orion ST SSAG and crayford & VSS+/ probably max weight 30#, right now using it on a CG-5 (this is to be my travel mount). Could possibly see getting a VRC @ about 18# down the road... Right now doing Video but don't want to not be able to do DSLR or CCD as I have in the past,,,, so not wanting overkill, but wanting enough :foreheadslap: :question: :question:,,, Kasey

#69 Mike X.

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Posted 22 October 2013 - 03:30 PM

Kasey,here is my 2 cents for what they worth.

Consider also the weight of the mount.
If you are going to use the CGEM DX permanently mounted, that's ok, but if you are going to assemble it and dissasemble it every time....hmm i think it's a beast.

I believe for video astronomy the CGEM or the NEQ6/AZEQ6 are more than enough for your C9.

#70 dragonslayer1

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Posted 22 October 2013 - 04:05 PM

Thannk you Mike,
I would use the JMI wheely bar I have. I bought it when I was using my CPC, it really is nice. From all I can gather sense last year they are identical x-cept the diameter of tri-pod legs. I have read some of the other brand mounts that that is a complaint, weak legs. I don't think Celestron has had that problem,, Kasey

#71 dpippel

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Posted 22 October 2013 - 04:45 PM

I routinely set up and break down my CGEM DX. IMO it's not that much of a beast to deal with, really. There's a reason that the tripod, mount, and counterweight shaft come apart and are manageable weights. ;)

#72 Stew57

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Posted 22 October 2013 - 04:48 PM

I can carry my CGEM with the mount already on the tripod out as a single unit. I add weights then ota. Doubt I could carry the DX tripod with the head already mounted. Would make another trip and having to mount the head on the tripod.

#73 mich_al

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Posted 22 October 2013 - 05:20 PM

Here is a solution that worked for me: http://www.scoperoll...m/casters.shtml

Though I don't see a CGEM DX set listed, unless the Celestron HD tripod he calls out is the right one. If it looks like a potential solution for you you could contact him. I've talked with him and he's pretty flexible.

#74 WesC

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Posted 22 October 2013 - 05:43 PM

I can carry my CGEM with the mount already on the tripod out as a single unit. I add weights then ota. Doubt I could carry the DX tripod with the head already mounted. Would make another trip and having to mount the head on the tripod.



Yep I do the exact same thing. And yeah the DX tripod is a LOT heavier. I would break it down if I had a DX, but it is still manageable.

#75 dragonslayer1

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Posted 22 October 2013 - 05:47 PM

Thats what I like about the Jmi Wheelybar, its a tripod looking thing and I put some boards across the bottom so have a small tray thats good for accessories etc, just wheel it out with all in one swoop,, but I view from my driveway.. They do make some for rough terrain tho.
Mark, can I ask what you run on your CGEM as far as weight?
Kasey






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