GEM advice

[Bob Vixie]

Hi Everyone,

I've had a Celestron CG5-GT mount for a couple years now. I'm not very happy with it. It's noisy, slow and I could never get the gears adjusted right to stop the backlash. So I have gotten rid of it.

So, I'm looking for something to replace it. I have a 7" Intes-Micro Mak-Cass, an AT6RC, and an 80mm refractor that I would use on it. The Mak is 15 lbs, but once I get other stuff on it, it will be a bit more.

Right now, this would be for visual use, but in the future, I'd like to get a camera and play with astrophotography.

So I'm looking at the next level of mounts. The CGEM, the Atlas, the GM-8 (used), the iEQ45. These are all in the $1500 range.

The one that's got my eye is the iOptron iEQ45. I've read lots of stuff on it. People generally like it. The measured PE on it is in the 20-30 arc-sec range. I think the mount I had was in the 80 range.

The mount comes in two forms. Their first release had four screws that tightened around the DEC head. While you could adjust it with these, it was hard to test the balance. Some just said balance on a dowel and mount at that point. They did modify the software to measure the motor current and give you an idea of balance that way.

The second form has a modified DEC clutch that contains a bearing so you can balance the gear right on the mount. It has a single lever like the CG5 that would release the head and clamp it down. This modified clutch is $100 more.

So if you have any advice on any of this, I'd love to hear it.

I'm sure I'll post more here as I think of more questions.

Thanks,
Bob

[Al Acker]

Try for a used CGE but expect to pay a fee hundred for mods to make it work correctly. On Jan 10, 2012 7:47 PM, "Bob Vixie" <bvixie@comcast.net (bvixie@comcast.net)> wrote:

Hi Everyone,

I've had a Celestron CG5-GT mount for a couple years now. I'm not very happy with it. It's noisy, slow and I could never get the gears adjusted right to stop the backlash. So I have gotten rid of it.

So, I'm looking for something to replace it. I have a 7" Intes-Micro Mak-Cass, an AT6RC, and an 80mm refractor that I would use on it. The Mak is 15 lbs, but once I get other stuff on it, it will be a bit more.

Right now, this would be for visual use, but in the future, I'd like to get a camera and play with astrophotography.

So I'm looking at the next level of mounts. The CGEM, the Atlas, the GM-8 (used), the iEQ45. These are all in the $1500 range.

The one that's got my eye is the iOptron iEQ45. I've read lots of stuff on it. People generally like it. The measured PE on it is in the 20-30 arc-sec range. I think the mount I had was in the 80 range.

The mount comes in two forms. Their first release had four screws that tightened around the DEC head. While you could adjust it with these, it was hard to test the balance. Some just said balance on a dowel and mount at that point. They did modify the software to measure the motor current and give you an idea of balance that way.

The second form has a modified DEC clutch that contains a bearing so you can balance the gear right on the mount. It has a single lever like the CG5 that would release the head and clamp it down. This modified clutch is $100 more.

So if you have any advise on any of this, I'd love to hear it.

I'm sure I'll post more here as I think of more questions.

Thanks,
Bob



Bob Vixie
StarMaster 20
Meade 12" Lightbridge/Argo Navis DSC
Intes-Micro M715/Celestron CG5-GT
Vixen ED80Sf/Vixen Porta Mount

[Bob Vixie]

Try for a used CGE but expect to pay a fee hundred for mods to make it work correctly.

Hi Al,

I think you missed the $1500 part... You really think used CGEs are in that range?

Bob

[Al Acker]

I've seen them go in the 1800 range ... you may get lucky as people who don't know about the mods can get very unhappy with them.

Al

----- Original Message -----
From: Bob Vixie (bvixie@comcast.net)
To: consulting@csastro.org (consulting@csastro.org)
Sent: Tuesday, January 10, 2012 9:55 PM
Subject: Re: GEM advice


Al Acker wrote: Try for a used CGE but expect to pay a fee hundred for mods to make it work correctly.

Hi Al,

I think you missed the $1500 part... You really think used CGEs are in that range?

Bob



Bob Vixie
StarMaster 20
Meade 12" Lightbridge/Argo Navis DSC
Intes-Micro M715/Celestron CG5-GT
Vixen ED80Sf/Vixen Porta Mount




-------------------- m2f --------------------

Read this topic online here:
http://www.csastro.org/forums/viewtopic.php?p=17330#17330

-------------------- m2f --------------------

[Bob Vixie]

I've seen them go in the 1800 range ... you may get lucky as people who don't know about the mods can get very unhappy with them.

Al

I was thinking of the CGE Pro which are much more.

Bob

[Stargazer_Ken]

Bob,

I haven't used it a whole lot but I like my CGEM. I chose it over the Atlas for two reasons. One is that it uses servos so it has a better chance of knowing where it is. The other reason was the built in polar alignment. Even if you can't see Polaris, you can get a decent polar alignment. Bottom line, is they will both do a decent job in the weight range you are talking about. They are a lot heavier than CG5-GT or the SkyView Pro mounts. Those will seem like grab and go mounts after a CGEM or Atlas. AutoGuiding is still likely a must for a longer focal length so take that into consideration as well. Also, I know for the CGEM, I had to get a Losmandy to Vixen dovetail adapter since the CGEM comes with the wider Losmandy dovetail. That was somewhere around $100. All my scopes used the narrower Vixen dovetail.

Ken


On Tue, 10 Jan 2012 22:55:45 -0600, Bob Vixie wrote:

 Al Acker wrote:
 Try for a used CGE but expect to pay a fee hundred for mods to make
 it work correctly.

 Hi Al,

 I think you missed the $1500 part... You really think used CGEs are
 in that range?

 Bob


 Bob Vixie
 StarMaster 20
 Meade 12" Lightbridge/Argo Navis DSC
 Intes-Micro M715/Celestron CG5-GT
 Vixen ED80Sf/Vixen Porta Mount

[Chris Peterson]

I wouldn't worry too much about periodic error. All mounts have too much
to use without PE correction, and PE correction essentially makes the
problem go away. I assume (but don't know for sure) that all these
mounts have PEC. Make sure of that, regardless of which you decide to go
with.

Also, make sure that an ASCOM driver is available for the mount you
choose. If it isn't, I'd pass, no matter how good the mount might be in
other respects.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 1/10/2012 7:50 PM, Bob Vixie wrote:

Hi Everyone,

I've had a Celestron CG5-GT mount for a couple years now. I'm not very happy with it. It's noisy, slow and I could never get the gears adjusted right to stop the backlash. So I have gotten rid of it.

So, I'm looking for something to replace it. I have a 7" Intes-Micro Mak-Cass, an AT6RC, and an 80mm refractor that I would use on it. The Mak is 15 lbs, but once I get other stuff on it, it will be a bit more.

Right now, this would be for visual use, but in the future, I'd like to get a camera and play with astrophotography.

So I'm looking at the next level of mounts. The CGEM, the Atlas, the GM-8 (used), the iEQ45. These are all in the $1500 range.

The one that's got my eye is the iOptron iEQ45. I've read lots of stuff on it. People generally like it. The measured PE on it is in the 20-30 arc-sec range. I think the mount I had was in the 80 range.

The mount comes in two forms. Their first release had four screws that tightened around the DEC head. While you could adjust it with these, it was hard to test the balance. Some just said balance on a dowel and mount at that point. They did modify the software to measure the motor current and give you an idea of balance that way.

The second form has a modified DEC clutch that contains a bearing so you can balance the gear right on the mount. It has a single lever like the CG5 that would release the head and clamp it down. This modified clutch is $100 more.

So if you have any advise on any of this, I'd love to hear it.

I'm sure I'll post more here as I think of more questions.

Thanks,
Bob

[Stargazer_Ken]

The CGEM has PEC correction but unfortunately I have other things going on that swamp the basic PE so it wasn't useful for me. From what I have read, even with PEC, you're still going to need auto guiding for any decent focal length. Some say you should use one or the other but not both as they will fight each other. I think autoguiding will generally be much tighter since with PEC you will likely still be in the range of 5-10 arcsec error on a good mount. That would be very noticable.

I agree whole heartedly about the ASCOM driver. On my Skyview Pro, I put iOptron motors and hand controller on it and though they provided an ASCOM driver, it never worked right. The CGEM works as expected.

The CGEM software has better built in features than the Atlas but the Atlas can use EQMOD which makes up for some of that and goes beyond.

Ken


On 1/10/2012 10:20 PM, Chris Peterson wrote:

I wouldn't worry too much about periodic error. All mounts have too much
to use without PE correction, and PE correction essentially makes the
problem go away. I assume (but don't know for sure) that all these
mounts have PEC. Make sure of that, regardless of which you decide to go
with.

Also, make sure that an ASCOM driver is available for the mount you
choose. If it isn't, I'd pass, no matter how good the mount might be in
other respects.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

[Al Acker]

I really like the CGE over the CGE pro... the pro is too tall for my setup and uses the same electronics as the normal CGE... the pro has a better cable system but you can mod the CGE to have even a better system.

Al

----- Original Message -----
From: Bob Vixie (bvixie@comcast.net)
To: consulting@csastro.org (consulting@csastro.org)
Sent: Tuesday, January 10, 2012 10:06 PM
Subject: Re: GEM advice


Al Acker wrote: I've seen them go in the 1800 range ... you may get lucky as people who don't know about the mods can get very unhappy with them.

Al

I was thinking of the CGE Pro which are much more.

Bob



Bob Vixie
StarMaster 20
Meade 12" Lightbridge/Argo Navis DSC
Intes-Micro M715/Celestron CG5-GT
Vixen ED80Sf/Vixen Porta Mount




-------------------- m2f --------------------

Read this topic online here:
http://www.csastro.org/forums/viewtopic.php?p=17332#17332

-------------------- m2f --------------------

[Chris Peterson]

If you are imaging, you ALWAYS want to train and enable PEC, even when
you autoguide. Autoguiding works better when it has less to correct. In
addition, autoguide corrections are limited to the guide speed-
typically 1x or 0.5x sidereal. Most mounts are capable of making faster
PE corrections, so if you have a high spot somewhere that produces a
position spike, PEC will fix it immediately, while autoguiding may not
fix it at all, may require several cycles to fix it, or may actually
overcompensate and make things worse.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 1/10/2012 10:54 PM, Stargazer_Ken wrote:

The CGEM has PEC correction but unfortunately I have other things going on that swamp the basic PE so it wasn't useful for me. From what I have read, even with PEC, you're still going to need auto guiding for any decent focal length. Some say you should use one or the other but not both as they will fight each other. I think autoguiding will generally be much tighter since with PEC you will likely still be in the range of 5-10 arcsec error on a good mount. That would be very noticable.

I agree whole heartedly about the ASCOM driver. On my Skyview Pro, I put iOptron motors and hand controller on it and though they provided an ASCOM driver, it never worked right. The CGEM works as expected.

The CGEM software has better built in features than the Atlas but the Atlas can use EQMOD which makes up for some of that and goes beyond.

Ken

[Bob Vixie]

Thanks for the advice guys. Here's what's leaning me toward the iOptron and some of my concerns...
Likes:
- It's way more portable (light) than what the other mounts look like. It looks like a AT clone, but way cheaper (not only in price).
- It's not a Celestron (sorry Al). The CG5 and Celestron support make me want something else. That's probably not logical.
- It has a good polar alignment scope. Reviews say it's very easy to setup and get good gotos with.
- It has spring loaded worm gears. This was one of my concerns, but after reading some, I think they are supposed to be good. Is that right?
- It has an ASCOM driver. In fact, the controller has a USB port on it for updating the firmware. I'm not sure if the ASCOM driver will run over that also.
Concerns:
- Worm gear springs. I'm still not sure if these are a good thing.
- The early models didn't have a good way to balance the scope on the DEC axis. The newer model does. Is this important?
- Speed. The CG5 was very slow (I thought). The reviews claim this one moves at 5 deg/sec. I expect that's much faster and would be fine.
- New. This mount was released last year. People on the forums seem happy with them, but I don't know how many problems new mounts have when they get released. Is it a big risk to get something that new?

Bob

[Bob Vixie]

If you are imaging, you ALWAYS want to train and enable PEC, even when
you autoguide. Autoguiding works better when it has less to correct. In
addition, autoguide corrections are limited to the guide speed-
typically 1x or 0.5x sidereal. Most mounts are capable of making faster
PE corrections, so if you have a high spot somewhere that produces a
position spike, PEC will fix it immediately, while autoguiding may not
fix it at all, may require several cycles to fix it, or may actually
overcompensate and make things worse.

Chris

Here's a link to some of the PEC data from the mount. I'm not up on any of that yet, but maybe you guys can interpret it...

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4198974/page/0/view/collapsed/sb/5/o/all/fpart/19/vc/1

Bob

[Chris Peterson]

- Worm gear springs. I'm still not sure if these are a good thing.

There is nothing intrinsically wrong with spring loaded worms. It's a
question of whether the entire system is properly designed. There are
some tricks to making a worm drive system work well, and they're
different for fixed or floating worms.

- The early models didn't have a good way to balance the scope on
the DEC axis. The newer model does. Is this important?

Yes. When you get into imaging, balance is critical. It's tricky with a
GEM (which is one reason I greatly prefer equatorial fork mounts). You
need to keep the RA axis heavy to the east (which means shifting your
weights slightly when you cross the meridian), and you need to have your
declination axis slightly preloaded- and the direction of preload can be
important, and can change when you shift to a new target (or cross the
meridian). So ease of adjustment is important to productivity.

- New. This mount was released last year. People on the forums >

seem happy with them, but I don't know how many problems new >
mounts have when they get released. Is it a big risk to get >
something that new?

New is always a concern. But I think you're pretty safe with something
that's been out there for a year, and has a good set of reviews available.

Have you had a chance to play with any of these mounts hands-on? Reviews
are one thing, but actually trying them could make all the difference.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 1/10/2012 11:31 PM, Bob Vixie wrote:

Thanks for the advice guys. Here's what's leaning me toward the iOptron and some of my concerns...
Likes:
- It's way more portable (light) than what the other mounts look like. It looks like a AT clone, but way cheaper (not only in price).
- It's not a Celestron (sorry Al). The CG5 and Celestron support make me want something else. That's probably not logical.
- It has a good polar alignment scope. Reviews say it's very easy to setup and get good gotos with.
- It has spring loaded worm gears. This was one of my concerns, but after reading some, I think they are supposed to be good. Is that right?
- It has an ASCOM driver. In fact, the controller has a USB port on it for updating the firmware. I'm not sure if the ASCOM driver will run over that also.
Concerns:
- Worm gear springs. I'm still not sure if these are a good thing.
- The early models didn't have a good way to balance the scope on the DEC axis. The newer model does. Is this important?
- Speed. The CG5 was very slow (I thought). The reviews claim this one moves at 5 deg/sec. I expect that's much faster and would be fine.
- New. This mount was released last year. People on the forums seem happy with them, but I don't know how many problems new mounts have when they get released. Is it a big risk to get something that new?

Bob

[Chris Peterson]

I don't know how that analyzer collects the data. To me, the curves
don't look very good- the noise on the sinusoidal component looks like
gear noise. But if the data collection is automated, say from an
autoguider, it could also be the result of guider error, and not true
tracking error at all.

If it's gear noise, it's high enough magnitude that you'd need to
autoguide even for short (30-second) exposures. Of course, I'd recommend
starting your imaging from the beginning with an autoguider and with
5-10 minute subexposures.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 1/10/2012 11:35 PM, Bob Vixie wrote:

Here's a link to some of the PEC data from the mount. I'm not up on any of that yet, but maybe you guys can interpret it...

http://www.cloudynights.com/ubbthreads/ ... rt/19/vc/1

Bob

[Bob Vixie]

New is always a concern. But I think you're pretty safe with something
that's been out there for a year, and has a good set of reviews available.

Have you had a chance to play with any of these mounts hands-on? Reviews
are one thing, but actually trying them could make all the difference.

Chris

No I haven't seen one in person. Just pictures and reviews. There have been a few come across Astromart while I've been looking. They seem to get bought up pretty fast, which is a good sign. None of the modified clutch version have shown up there yet. I'm kind of leaning toward buying a new one anyway. I've bought a fair amount of used stuff off Astromart (and I've done ok), but maybe not this time.

I forgot to mention it comes with both Vixen dovetail and Losmandy mounting plates. Also a built in GPS and a heated controller so it will work at very low temps (not that I work well at them).

Bob