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Calling all G11 owners

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#1 imhotep

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Posted 06 April 2009 - 08:53 PM

My goal here is to become better informed about the alleged limitations and out-of-the-box issues with the Losmandy G11. I'll get more specific in a bit.

Years ago when I got into astrophotography I went through that phase where I was looking up as many online galleries as I could find. When I was done drooling over the amazing images, I took note of the equipment that was used as a means of educating myself on what it might take to work my way towards shooting my own astrophotos. Underneath all the best images I kept seeing names like "Losmandy G11", "Astro Physics Mach1 GTO", and "Orion Atlas EQ-G".

That was before I knew squat about PE though. It was before I had gone through the process of polar-aligning a GEM with awkward alt/az manual controls. And, it was before I bought into the 'hypertuning' of an Orion Atlas EQ-G and spent the better part of a year being disappointed with the results.

Currently I'm in the market for what can hopefully be the last mount I buy for many years. I was set on the G11 until my astronomy buddies started forwarding me some articles that make the G11 sound like it needs just as much tuning and customizing as an Atlas EQ-G. I'm on the tail-end of a very long and unproductive year with an Atlas EQ-G, so I'm no longer interested in buying a mount that requires dissessmbly and tuning to get the performance I need.....at any price, much less $3500.

This article in particular paints a grim picture:
http://www.astro.uni...g11_tuning.html

Is the current version of the G11 still loaded with potential for erratic PE and racey stepper motors?

There's also mention of replacing the worms with hi-precision ones. Again, not encouraging for a $3500 mount, but I don't know for sure if these things are still what you'd call 'current' considerations with the G11.

Have any of these issues been corrected by Losmandy such that the current version needs less modification than previous ones?

If my budget were larger this thread would be unnecessary. I'd buy an AP Mach1 GTO and be set. The G11 is just barely within my reach though, so I'm trying to inform myself of what I would actually be getting for my $3500.

I greatly appreciate any insight you can offer me on the use of this mount for long-exposure CCD astrophotography. If it's helpful, the rest of my imaging equipment is as follows:

8" f/5 newtonian astrograph (FL=1000mm)
QHY8
Guided via 80mm f/5 achromat with the Orion SS autoguider

An SBIG ST-2000XM or ST-10XME may be in my future as well, but either way I'll be imaging at 1000mm with pixels in the range of 6.8 - 7.8 microns. Ideally I'd like the mount to give me tight stars in exposures up to 10-minutes. This isn't even a lot to ask for some Atlas owners, so I assumed the G11 could hack it or better.

Thanks for your help.

#2 ZRX-Steve

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Posted 06 April 2009 - 10:31 PM

Pre 2001 the worm gears could cause erratic behavior. Later versions had a stainless steel worm gear, and the newest ones have a bronze worm gear which is supposed to be the best.

There is a French Company called Ovision that had a $500 precision worm gear, but from what I understand it's not necessary on the newer mounts. The current brass worm is quite good.

The indexing on the older polar scopes expires in 2010, but the new scopes are good from 2003 through 2030.

A common mod for older G11's was swapping out the Hurst motors for SAIA to reduce stepper vibration. I can't find the exact information, but I believe that Losmandy started shipping G11's with SAIA in 2003.

In short, I think the article is referring to a vintage G11, and I don't think it's valid with contemporary G11 mounts. In fact, I believe you will find that a new G11 out of the box will exhibit PE less than most mounts can be tuned to (< 10"), and a PEMPro training will reduce it below 5". (http://www.ccdware.c...ro/examples.cfm)

#3 blueman

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Posted 06 April 2009 - 11:09 PM

One thing that you have to understand, people with problems are the most vocal and one article will continue to circulate even it is not longer applicable. The number of articles that I have seen where problems were stated to be rampant, were very few.
I have a newer 2008 model of the G-11 and it worked very well out of the box. I have modified it a lot, with Ovision worm, precision gearboxes and tuning, but that was because I wanted to, not because it did not work well.
But even if you took the $600 I spent on mods, the cost of the mount with Gemini was under $4,000 and my PE is now +- 2.3" uncorrected, which is as good as most any mount that cost considerably more.
Do you need to do mods, no. Do mods improve the mount, yes. Is the mount worth the money, yes. Is the mount perfect, no. But I feel it is as good a mount for under $4,000 as any out there.
I use mine for imaging.
Blueman

#4 skybsd

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Posted 07 April 2009 - 01:39 AM

Hello,
I'll simply cut straight thru to your questions..,

Is the current version of the G11 still loaded with potential for erratic PE and racey stepper motors?


If you're referring to the ""76-second error", yes.

There's also mention of replacing the worms with hi-precision ones.

<snipped>

Have any of these issues been corrected by Losmandy such that the current version needs less modification than previous ones?


No

If my budget were larger this thread would be unnecessary. I'd buy an AP Mach1 GTO and be set. The G11 is just barely within my reach though, so I'm trying to inform myself of what I would actually be getting for my $3500.


You've already started answering the fundamental point of your post yourself :smirk:

Others may well have their opinions, but there simply is no mount out there that delivers "long-exposure CCD astrophotography" capability out of the box for ~ (US)$3500.00.

IF you are really set on sticking to your stated preference to not tune or swap parts in order to get the performance you seem to want - after shelling out for the mount, then you need to keep saving for another, more appropriately designed mount system.

Hope this helps.

Regards,

skybsd

#5 tidroplane

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Posted 07 April 2009 - 01:52 AM

I have a 2006 G-11, worked great right out of the box, it has servo motors instead of stepper. I have done no mods to the mount and it continues to perform beautifuly. If you can autoguide, the mount will not let you down for long exposure, 10 min. subs...no problem, I would go longer but my skies limit me. For me personally, the G-11 was money well spent.

#6 Kaizu

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Posted 07 April 2009 - 04:07 AM

I have similar mount as David and I'm quite happy with it.
I checked the unguided PE and it was inside 5". I normally use 2130 mm focal length and 30 sec. exposure time and I do not need the autoguider. The LP limits the exposure time.
I'm going to use narrow band filters, then I need longer exposures and also quiding. I think that G11 is best mount in the middle price class.
I have followed the F1 racings. The cars are fastest in the world but still the teams develop something new for next season to get them still faster. I think that there is not so good mount that it couldn't be better.

Kaizu

#7 Charlie Hein

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Posted 07 April 2009 - 06:48 AM

Curt - let me attempt to give you my perspective on this, having been down almost the exact road you're on right now.

I think that you may be confusing ease of operation "out of the box" with the idea of a "maintenance-free" mount. Hopefully I can separate these two concepts for you. Let's start with what I believe to be the myth of a "maintenance free" mount.

IMO, I seriously doubt that you'll ever find any piece of precision equipment that is completely maintenance free. If for no other reason than the fact that we live in a dusty and dirty world it's just a matter of time before any mount you own will need maintenance just to keep it clean internally. You wouldn't expect to buy a car and not maintain it, would you? The same is true of your mount, particularaly if you've laid out a lot of cash for one and you plan on keeping it for a long time.

So, IMO it's a given that no matter which mount you get, if you plan on keeping it for a very long time then eventually you'll need to clean and regrease it. Once you take it apart to do this then you're going to need to put it back together in at least as good a working order as you found it. This would be things like setting the worm gear mesh and the loading on the bearings correctly.

Seems to me that since the need for this is a given, we either have to:
  • learn how to maintain the mount ourselves
  • pay someone else to do it
  • or sell off the equipment (hopefully) before it is damaged or wears out from inattention
At the bottom line for me I realized that I don't want to have to to send my mount off to be maintained. I'll need to know how to maintain it myself. Once I resigned myself to this it turned out to be a major steering factor in my decision to purchase the G-11.

Now - about ease of operation "out of the box"... IMO at the bottom line this seems to be very much a matter of how much money you have to spend. Your budget is looking a lot like mine was - AFAIK, at that price point you're really looking at either a CGE or a G-11 if you're buying new. I do not think that either of these mounts has a real "out of the box" performance edge over the other when you get right down to it. I wish that I could tell you that at this price point you won't have any issues to overcome but I can't. Even though I had no complaints with the way the G-11 worked for me, others have not been so fortunate. You can read plenty of posts where folks were either pleased or troubled with the CGE, too. At the bottom line here I think that you'd have to spend a good deal more cash to have a better chance at getting something that works nearly perfectly "out of the box" - but at the ~$3500.00 price point the chances are certainly very good that you'll end up with a *perfectly acceptable* performance from your new mount. IMO, if your budget says $3500.00 then your expectations should be set accordingly - expect *perfectly acceptable*, not *perfect*. Chances are you'll be pleasantly suprised at how things work out.

Personally, I steered toward the G-11 on the basis of needing to maintain the mount over time. When I looked at the CGE and G-11 it seemed to me that the G-11 looked much easier to take apart and adjust than the CGE. Losmandy also sells pretty much every part on the mount as a "spare", too. I really like that - if anything breaks I should be able to fix it pretty easily.

I really liked my Atlas, but it wasn't the easiest mount to work on, and it I was never able to get replacement OEM parts for the internals, which annoyed me to no end. This was a major "tipping point" in my decision to get a new mount and I think that the G-11 will be much easier on me in this regard. The other thing that pushed me over the line was the desire to get into longer focal length, higher resolution astrophotography. You seem to be at the same point I was when I made the jump.

The G-11 is working just fine for me in this regard. I have an SBIG ST2000XCM and with my C9 at f/6.3 the resolution comes in at just over 1 arcsecond per pixel. It's a really sweet spot for galaxies and such. Here's what the setup can do with 10 minute exposures and an hour's worth of time:

Posted Image

Since 10 minutes is well over the worm's period, you can literally expose as long as you need to. That's *perfectly acceptable* performance for me...

Charlie

#8 Strgazr27

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Posted 07 April 2009 - 07:14 AM

Curt,

The 76 sec error is IMO, overblown a bit and it can be worked around as both Charlie and my images show. Take the time to make sure the worm blocks are aligned and adjusted corretly and the 76 component is easily guided out. It does make the use of PEC a little more difficult but if your getting the performance that Charlie, Floyd and my self are getting there is really no need for it.

#9 imhotep

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Posted 07 April 2009 - 08:29 AM

Thanks everyone for the helpful testimonials. This is mostly what I was hoping to hear. As usual my first round of questions has led to others....

Regarding the 76-second error, I want to make sure I understand exactly what is being said. Is it to say...

1. that there's a PE spike measuring 76 arcseconds (lol, probably not but I wanted to ask anyway)

or

2. that there's a PE spike of some magnitude that comes around every 76 seconds

or

3. that there's a PE spike of some magnitude that comes once per cycle at 76 seconds into the period.

#10 imhotep

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Posted 07 April 2009 - 08:37 AM

Charlie, I'm really glad you found my thread :)

Personally, I steered toward the G-11 on the basis of needing to maintain the mount over time. When I looked at the CGE and G-11 it seemed to me that the G-11 looked much easier to take apart and adjust than the CGE. Losmandy also sells pretty much every part on the mount as a "spare", too. I really like that - if anything breaks I should be able to fix it pretty easily.


I'm very glad to hear that. Trying to get parts and info from Orion hasn't been pleasant.

I really liked my Atlas, but it wasn't the easiest mount to work on, and it I was never able to get replacement OEM parts for the internals, which annoyed me to no end. This was a major "tipping point" in my decision to get a new mount and I think that the G-11 will be much easier on me in this regard.


I really needed to hear this especially.

Thanks for posting the image of M51. I couldn't ask for a better example for my purposes. It's the same camera I mentioned at a FL roughly 1.5x what I'll be using most of the time.

#11 imhotep

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Posted 07 April 2009 - 08:48 AM

I just wanted to clarify something real quick, in case I've confused people or contradicted myself.

IF you are really set on sticking to your stated preference to not tune or swap parts in order to get the performance you seem to want - after shelling out for the mount, then you need to keep saving for another, more appropriately designed mount system.


For a guy with my budget in a hobby this expensive, preferences don't always work out. When I wrote this thread I was ready and willing to compromise on what is probably an unrealistic goal of affording a mount like the Mach1GTO any time soon, but that may not have come across correctly.

Do I want an AP mount. You betcha. I can't afford one though, so before I invested in what I CAN afford, I wanted to tap the community and see if I was about to sign up for an equally agrivating experience as I've had with the Atlas. It sounds like the G11 needs less tuning and is easier to work on to boot.

Maybe it's silly, but I was hoping the G11 gurus would calm my paranoia about this mount, and so far you guys are doing great ;)

#12 EricJD

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Posted 07 April 2009 - 09:44 AM

And besides, the Losmandy's are just so darn cool...

#13 Carl M

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Posted 07 April 2009 - 11:40 AM

I have a new ( purchansed in Jan of 2009) G-11 with Gemini. Gemini does not use stepper motors - they are servos. The non-gemini mounts have steppers. I also have an older ( circa 1999) GM-8. Huge difference. I can get 4 min subs as tight as can be out-of-the-box with the G-11. I put in new brass worms in the GM-8 and it too is spot-on, even with older stepper motors.

#14 Charlie Hein

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Posted 07 April 2009 - 11:54 AM

2. that there's a PE spike of some magnitude that comes around every 76 seconds


The bearing blocks that hold the G-11's worm gear are individual units that basically slide onto each end of the worm gear and bolt to a plate to hold the worm gear against the worm wheel. Because these units are separate they can become misaligned with the worm gear shaft and bind the shaft against the bearings inside the block (or this can possibly also happen if the bearing inside the block is misaligned but I've only heard of one confirmed case of this). The telltale that this is going on happens at 76 second intervals continuously. Almost all stock G-11's will have this "tic" in PE to some extent. Mine had it - in fact it still has it, although the amplitude of the "tic" is so minimal at this point as to be inconsequential.

The cheap fix for this is to carefully align the offending worm block so that the bearing is as square to the worm gear shaft as possible. Depending on how the bearing is out of square, this might invlove shimming under the block on one side or corner. In my case all I really had to do was make sure that the block was square by using a feeler guage to square the block assembly against the body of the mount. It's a good idea to do this anyway when setting the worm/wheel mesh as it also squares the worm against the wheel.

Another way to completely eliminate the "tic" is to replace the worm blocks (and worm) with the monolithic worm block and worm from Ovision. One nice thing about this system is that it makes the worm mesh procedure somewhat easier to do. An additional take away from this option is that for nearly every G-11 it improves the overall PE significantly. However, going this route is going to be somewhere around $500-$550. By every account I've read it's a good upgrade, but so far I am happy with how the mount is working and I'm not inclined to go that route. You may feel differently.

Charlie

#15 blueman

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Posted 07 April 2009 - 12:17 PM

I would also like to add that the 76 sec error is not normally a large one, but many times it is sub arc sec in amplitude. This is not an issue for most people. In fact, not everyone has this error, but as was mentioned, it is present in most all G-11 mounts. But, there are errors in the worm that will likely be greater than the 76 error.

I have taken 6 min unguided exposures with my G-11 when it was stock and they looked very good, with almost no discernible elongation of the stars. In fact, they looked as good as many guided shots I reviewed.

One of the things to consider is the image scale you are proposing to use. If you are going to take 1" or less, then every PE error is important. If you are taking 3" then most small errors will be guided out completely.

It is just a fact of life that to achieve near perfection cost a lot of money. If you spend $15,000 on a mount, you will get close to perfection. If you spend $1,500 you will come no where near perfection. :cool:

A mount that cost $9,000 like an AP900, will definitely out perform the G-11 at $3,500. But a G-11 tuned and modified for a total cost of $4,000 will knock on the door of the $9,000 mount as far as performance is concerned, but not in load capacity. There is just only so much that one can buy for $3,500, even though it is a bit of money. High end mounts are at least $9,000 and can be much more than that.
Floyd

#16 imhotep

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Posted 07 April 2009 - 12:58 PM

This may seem like a petty detail, but how is the polar scope on the G11?

One thing that irks me about my Atlas (and my CG-5 ASGT before that) is the clumsy polar-scope adjustment screws. I have yet to really dial in the polar-scope on my Atlas despite all my efforts. Last week I dissected it and realized I could probably machine a kit that would replace some of the parts and result in a centered crosshairs that never move or need to be adjusted.

Just curious about how the G11's polar-scope stacks up.

#17 Charlie Hein

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Posted 07 April 2009 - 01:32 PM

This may seem like a petty detail, but how is the polar scope on the G11?

One thing that irks me about my Atlas (and my CG-5 ASGT before that) is the clumsy polar-scope adjustment screws. I have yet to really dial in the polar-scope on my Atlas despite all my efforts. Last week I dissected it and realized I could probably machine a kit that would replace some of the parts and result in a centered crosshairs that never move or need to be adjusted.

Just curious about how the G11's polar-scope stacks up.


What I like about it - unlike the Atlas you can spin the polar scope without having to rotate the mount in RA. The reticle is a very nice etched glass and gives you up to three stars to line up on if your sky is dark enough. I have yet to really need to drift align the mount when using the polar scope.

What I don't like about it - the illuminator is external, the battery case is very clunky and does not come with a dimmer. I have taken to shining a red flashlight down the illumiator hole rather than using it. That really is my only complaint with it.

I saw a very nice illuminator on a club members GM-8 that was much better - a small tube less than 1/4" in diameter and about two inches long - but you'd have to be careful not to break it. It seemed really fragile to me.

Overall I'd say that the polar scope is well worth the money because it will certainly save you enough time to pay for itself many times over.

#18 imhotep

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Posted 07 April 2009 - 01:38 PM

Thanks Charlie. One more on this topic - is the polar-scope on the G11 adjusted using three screws, or is it permanently centered requiring no adjustment?

#19 Charlie Hein

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Posted 07 April 2009 - 01:40 PM

It's very much like the Atlas but the adjustment screws are teeny-tiny. I did not need to adjust mine, when I screwed it in it was dead-on.

#20 mnaf

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Posted 07 April 2009 - 02:20 PM

Have you considered a Tak EM200? Excellent tracking and painless polar alignment from all accounts. There's fantastic work being done with them and I've seen some complete systems for not much more than your budget.

#21 Dave M

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Posted 07 April 2009 - 02:37 PM

What I don't like about it - the illuminator is external, the battery case is very clunky and does not come with a dimmer. I have taken to shining a red flashlight down the illumiator hole rather than using it. That really is my only complaint with it.


Charlie, i have one of these, the first generation version
and it works great.
http://www.4saleusa....ric/dimmer.html

#22 imhotep

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Posted 07 April 2009 - 03:06 PM

Have you considered a Tak EM200? Excellent tracking and painless polar alignment from all accounts. There's fantastic work being done with them and I've seen some complete systems for not much more than your budget.


No I hadn't, but maybe I should educate myself. Tak seems to have a lot of proprietary stuff though.

#23 Strgazr27

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Posted 07 April 2009 - 03:12 PM

You'll rarely see a used 200 for less than $4000. The payload is considerably less than the 11 and GoTo will rely on planetarium software.

On the plus side the polar scope is stupid accurate and they track extremely well.

A G11 can be made to track just as accurately, with a higher payload at a cheaper cost. I will say though, the NJP I owned was an amazing mount and the 200 should posess all the TAK qualities also. You just are going to pay for them in dollars instead of time.

#24 mnaf

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Posted 07 April 2009 - 03:20 PM

Moreso with their scopes, I think. There's a lot of components out there - Cassidy, etc..

It may not change your course but it'd probably be worthwhile to check them out. People who have upgraded to EM200's rave about them and the polar scope is probably the best in the industry. 15+min. guided shots with the quick polar scope alignment (that's probably conservative).

I've never heard of anyone needing to upgrade or "tune" a Takahashi/EM200 for better performance...

P.S. I believe the Atlas' counterweights are compatible with the EM200's! That can save a bunch.

#25 imhotep

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Posted 07 April 2009 - 03:38 PM

Ok Mike, you've peaked my curiosity. I'll look into it. I'm assuming that the EM200 will natively interface with MaximDL, The Sky 6, etc?

I might be willing to go $4K if it doesn't need tuning :crazy:






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