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Equipment Discussions >> Mounts

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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5736707 - 03/16/13 05:33 PM

if you are using pempro to read your PE, it throws away non integer harmonics, hence the 8/3 doesn't show up.

pecprep does show the harmonic, its the 181-second term.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5736822 - 03/16/13 06:21 PM

Hi,
I was using Pempro at that time. No wonder I never saw it. After trial period ran out and I switched to PecPrep. I just looked and it did have the 8/3 but it was not very high. It was about the same level as all the other spikes. I guess I was lucky. I am concerned about it now.

neilson


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gdd
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Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5737276 - 03/16/13 09:05 PM

Celestron's new AVX mount has integral gear ratios to make PEC more effective. I would think they would use AVX technology on a CGEM sized mount at some point, hopefully soon.

Gale


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: gdd]
      #5737880 - 03/17/13 01:26 AM

yup.. hence the theory "CGEM AVX"

I still have my CGEM, and maybe at some point Celestron will offer the AVX motors as a retrofit. It might be in the $400 range for both motors (and probably the motor board). So yet another case of throwing good money in after bad...

Neilson, Derick has stated that the 8/3 is generally around 6". So that's 6" that will never go away. But on mine, the 8/3 is 22" !!!!!! so even after putting in an Aeroquest worm, I could not get the PE (after PEC) below about 25".

I used the CGEM last night, and I realized that in spite of the good software it has (in addition to the irredeemable 8/3) a few other really annoying flaws:

1) the thumbscrew on the counterweight hurts your fingers, and you have to torque it down really tight because the rubber tip gives

2) the C/W shaft is non-beefy and cheesy

3) there is play in both RA and DEC even when everything is tightened down

4) the adjustment screws are rough in pitch, and there's a lot of friction/stiction when adjusting the azimuth

5) (worst of all) it is very heavy. Really bad weight-to-payload ratio.

That said... I would recommend purchasing pempro. The polar alignment routine is golden. better than ASPA! I easyly got within 2 arc-minutes of the pole with two of my mounts last night. About 15-20 minutes per mount.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738040 - 03/17/13 05:37 AM

Hi,
Wow, thats really bad 8/3. Can the 8/3 be guided out with PHD guiding. If not how can anybody possible image with it. Or is it only bad in some older models.

I have read Derek say, and he told me himself, that he thinks only a very small percentage (less than 10%) of people image at all. I dont know where he gets that, if its based on sales of their imagers or not. But I feel most imagers use Canon Dslr cameras or SBIG or other high end cameras. Then he said that he thinks only a small percentage of those few do long exposure and a small percentage of them use long fl. Therefore fixing the 8/3 is of little importance.
I dont know if he tells Celestron this or they tell him. But I find that to be a poor attitude for a telescope company to have. And its a poor excuse to not fix it.

I can't believe that most poeple buy expensive ota's and CGEM mounts just to look at Planets and M42 and a few bright galaxies. No offence meant to visual observers.
I live out in the country with fairly dark skies but I expect that most use their equiptment in light polluted cities and can't see much at all and after a while move up to imaging.
Celestron upgraded the CG5 to the Advanced VX with new non 8/3 motors so I would think that it was so people could image with it better.

All this is making me wish the Atlas had a CGEM DX/Cge Pro mount. Or that the CGE Pro was more affordable. This decision is getting harder to make. I'm worrying, will I get another good CGEM DX like I did the first time before or will I get a bad one like the replacement ones they sent me after that.
I need another option.

neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738065 - 03/17/13 06:23 AM

Neilson, the bottom line is, with an 8/3 as big as mine, guiding is mandatory. The 8/3 has a roughly 182-second period, so it can be guided out.

Derick's assumptions about how many are affected by the 8/3 is just that - assumptions. But the fact that Celestron changed to an all integer gearbox in the AVX, means that they acknowledge this issue.

The thing is, the lower the PE, the less you need to guide. I've heard tales of guiding corrections every 30 seconds, and I now believe that... After last night's pempro drift alignment, I got a 10-minute unguided sub at 600mm with round stars. Of course this was on my 0.5" PE (after PEC) AP.

But really if PEC worked well on a hypothetical CGEM AVX, I expect residual PE below 5". Which would be pretty good...


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738110 - 03/17/13 07:25 AM

I'm glad it can be guided out but I'm like you I want low PE so guiding isn't needed. But I am realizing thats not possible with my budget. I still want low PE so my guiding will be smoother.
With that first CGEM DX I had I got 12+ minutes guided and 5 minutes unguided and 8 minutes unguided with PEC on if I remember correctly. The unguided weren't perfectly round stars or consitant but I was happy with the tests. I knew I could image for 2 or 3 minutes with PEC on when I didn't feel like setting up the computer. The huge tripod and thicker weight bar helped alot, especially on windy days.

I wish I could get an AP mount but ever since I became disabled and can't work on aircraft avionics anymore my income wont allow it. And I havent seen used ones very cheap. Or I would get one.

neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738124 - 03/17/13 07:57 AM

To my knowledge, the only mounts that cost less than AP's and can hit AP performance are... G11's with the Ovision worm. Your issues with the Gemini 2 are terrible to hear about, but I've a few friends with the Gemini 2 and their experience is nowhere as bad as yours. Still for $1600 you certainly expect and deserve better.

If you can tolerate having no mount for a few months, I'd wait for a "CGEM AVX." That way you don't spend twice. The CGEM DX has the same 8/3. The CGE does not, but then it'd be used.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738276 - 03/17/13 09:44 AM

Yes waiting for an AVX version would be ideal but I might end up waiting for something not coming anytime soon. And miss the sale going on now. It would be nice to have some inside information about now.

Hay Celestron send me an email and let me know. I'll keep the secret. They probably think I would buy both, they are mistaken. The value of the old one would drop too much for me to sell.

I've never seen a used CGE Pro but If it looked nice I might buy one.

neilson

neilson


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738357 - 03/17/13 10:36 AM

I just located a used CGE for $1775.. I'm not familiar with their problems though

neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738505 - 03/17/13 12:23 PM

Cable problems. For that price it probably doesn't have the Bennett mod. That's a pretty good price actually.. IMHO a better choice than a CGEM DX, since at least the CGE is Made in USA and has Pittman motors (with no dreaded 8/3). I am not sure about the spares situation though.

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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738624 - 03/17/13 01:32 PM

Hi'
It has upgraded RA/DEC cables from scope and stuff and ADM knobs. He claims to have been used fewer than 20 times and is in excellent cosmetic and operational condition. The pictures look great. also with original boxes.

neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738688 - 03/17/13 02:07 PM

Between this and a CGEM, I'd probably go for this.

No warranty, but then no 8/3 either. Pretty much same price.

Looks like Celestron still stocks parts -
http://www.celestron.com/astronomy/parts/cge-mount.html

I can't see the prices, as I'm not in the US. So the situation with the CGE is exactly the same as with any other used Celestron mount.

Look at the picture of the motor - it's a Pittman

not a cheap made in India Igarashi.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738764 - 03/17/13 02:41 PM

Hi,
The motor board is $237 and the motor is $383. lots of mark up there but at least their available. I really like that about Celestron, you can buy parts. But if you touch anything, even the backlash adjustment when its under warranty they threaten to void the warranty.

neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5738774 - 03/17/13 02:44 PM

If you price the Pittmans separately they are still north of $200. A far cry from the $20-odd motors in the CGEM and CGEM DX (and CG-5).

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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5738957 - 03/17/13 03:48 PM

I contacted the seller and its a 2006 model. I was about to buy it at the $1775 price but someone else is trying to buy it now and I'm not going to play bidding games. There will be others.

neilson


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5739891 - 03/18/13 12:15 AM

Hi,
I ended up buying the CGE for $1625. I am sure I will be happy with it.
neilson


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? [Re: neilson]
      #5739919 - 03/18/13 12:37 AM



Much better choice than a CGEM DX, congratulations!

Probably a good idea to go for the Bennett mod though.. and with the money saved you'll have some funds for parts if ever.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: Replace GM-8 Gemini I w/ Atlas? [Re: neilson]
      #5740481 - 03/18/13 11:12 AM

Quote:

Hi,
I ended up buying the CGE for $1625. I am sure I will be happy with it.
neilson




Neilson,

To be honest, based on the problems that you have had, I'm sure that you will not be happy with the CGE. While it is a good mount, it has many of its own problems including a dead zone in the DEC axis that can be very problematic for calibration purposes. As with many things, this problem varies, but with the demands that you tend to place on mounts, I expect this to be a problem for you. The CGE is no better than a G11 and can easily be worse. If you don't end up happy with the CGE, you really need to save and move up to something like an AP after this. I think that you are wasting a lot of time and money on lower end mounts looking for higher end performance.


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jrcrillyAdministrator
Refractor wienie no more
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Reged: 04/30/03

Loc: NE Ohio
Re: Replace GM-8 Gemini I w/ Atlas? [Re: orlyandico]
      #5740505 - 03/18/13 11:22 AM

Quote:

... and homing switches!!!

Yes, a CGE is a good alternative at $2000. You'll even have some money left over after selling the G11 for the Bennett mod.

and if the periodic error on the CGE is not to your liking, Aeroquest sells a replacement ring gear for $250. Not sure why Jim doesn't sell a worm though..

Overall a superior choice to the CGEM DX.

John - I bet that new Tak handset will be $1000. The old one was..

So $6000-odd for an EM200, another $1000 for the handset. No thanks, I'd rather have a Mach1..!




I miss the homing swithes - great feature! The Tak handbox will surely be $1000 but with good used EM-200s going for not much over $3000 you'd be at $4000, which sounds like a great value to me.


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