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Question for Losmandy Imagers

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#1 waassaabee

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Posted 25 February 2009 - 11:59 AM

I've read that the GM-8 and G-11 mounts have instrument capacities of 30 and 60 pounds respectively. Most folks say cut that in half for imaging. Is that the case with the Losmandy mounts?

#2 Jared

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Posted 25 February 2009 - 12:25 PM

I've read that the GM-8 and G-11 mounts have instrument capacities of 30 and 60 pounds respectively. Most folks say cut that in half for imaging. Is that the case with the Losmandy mounts?


I can't speak to the G11 as I have never used one, but I imaged with a GM-8 for about 18 months with a range of equipment. I would say that the GM-8 is good up to 20 pounds with a reasonably short optical tube. I pushed that to twenty five pounds for a little while (with a light guide scope) and was not happy with the results. At least with my sample, 15 pounds would be quite conservative for imaging, 20 pounds was reasonable if the tripod was kept at minimum height, and 25 pounds was really pushing it.

#3 nighthound

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Posted 25 February 2009 - 12:59 PM

Gary, I've loaded my G-11 down in the past with about 40-45 pounds and it wasn't happy, nor I. I've since lightened my optics to a Vixen R200SS/Sky 90 or Sky 90/FS-60C side by side and the mount has behaved very well. My G-11 seems happy between 20-30 pounds max and even better with the lighter 90/60 combo. Learning to perfect balance a side-by-side set up has helped in a big way.

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#4 blueman

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Posted 25 February 2009 - 01:56 PM

Much of the answer for this lies in the type of scope you are mounting.
A long scope would be more of a problem than a short scope for instance. So a 6" f/11 would be more of a problem than a 12" SCT, though the weight might be very similar.
I have not used more than 35-40 lbs on my G-11, so I am not certain about the actual max.
However, I do know those that push the 60 lb limit and get good results.
How well you balance will also have an effect as would a permanent pier in an observatory.
So, I do know those that do 60+ lbs with the G-11 and they say that there is not a problem. But that said, any mount loaded to its limit is not the best situation in my opinion.
So, if you need 60 lbs of gear, then a G-11 is not the best choice, maybe an AP1200 would be a much better one for that load. You never know if you will be increasing the load later! :)
Blueman

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#5 D_talley

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Posted 25 February 2009 - 02:11 PM

I am one of the guys who loads his G11 to the max. I have a Meade 14 inch OTA that weights in at around 65 lbs on the mount. Works great for me since I am shooting with the Hyperstar system (F2). This would not work well if I shot at F10 or even F6.

#6 waassaabee

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Posted 25 February 2009 - 03:59 PM

Thanks all!! This info is very encouraging as I am getting near the time to move up to the next level in equipment. The GM-8 is looking like a real contender, but I keep telling myself might as well go G-11.

#7 rsbfoto

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Posted 25 February 2009 - 05:15 PM

Hi Gary,

It all depends how the mount behaves and what you have underneath. Also if you are prepared to tune it or not.

Last weekend I made some tests and here here is a nice result. 240s unguided image with 3000mm focal length ( Mewlon 250S f12). That night I made a ttal of 15 images NO guiding and 9 images came our woith very nice round stars. I even have 4 images one after the other with round star which means that for a period of 16 minutes the mount had no periodic error. That night it was even a little bit windy. Here you can see a screencopy of my weather station for that specific imaging hour.

That is from a G11 with a total load of about 55 pounds equipment and 55 pounds of counterweight.

#8 waassaabee

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Posted 25 February 2009 - 08:30 PM

Rainer, Thanks for the encouragement!! That's a helluva Horsehead you have there!! The more I think about it, the more it makes sense to turn up the gain a bit and go with the G11.. The $ difference for the extra capacity seems worthwhile.

#9 hersey0308

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Posted 25 February 2009 - 08:38 PM

hi gary - i love my gm 8 but if i had it to do over, i would take the g11 simply to give me flexibility for heavier imaging configurations. the attachment is the gm 8 with about twenty five pounds. it did work but only after lots of attention to balancing. with 25 lbs on board i was on "pins and needles" for both sessions but the images came out well.
nonetheless, everyone will agree the gm 8 is quite a handsome piece of business.

best
david

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#10 Joselo

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Posted 25 February 2009 - 08:39 PM

Rainer,
have you done any updgrades/tuneups to your mount?

#11 rsbfoto

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Posted 25 February 2009 - 09:09 PM

Hi,

Yes. I made the first one piece wormblock It was maybe 3 years ago. Nobody wanted it because of the price of roughly US $ 450.00. Nowadays the Ovision worm for US $ 500.00 is selling like warm rolls :). The RS-Wormblock has ball and thrust bearings inside. which is not the case fot the Ovision worm. Risk of having the 76second error due to the preload of the ball bearings.

Here it is assembled

Also I have the latest brass worms from Losmandy. All Losmandy mounts now come with the brass worm.

The next tune up is the gearbox exchange. The first one to do this tune up is Floyd. The PE is not so nervous anymore (small jumps up and down with a very high frecuency per second) according to the ones who already exchanged the standard gearboxes for McLennan gearboxes.

The whole tune up for one axis is about US $ 550.00 to 600.00, but if you ask me it is good spend money.

#12 Jared

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Posted 25 February 2009 - 10:25 PM

Rainer, Thanks for the encouragement!! That's a helluva Horsehead you have there!! The more I think about it, the more it makes sense to turn up the gain a bit and go with the G11.. The $ difference for the extra capacity seems worthwhile.


If you don't absolutely need the extra portability of the GM-8, I would definitely recommend the G11 instead. The extra capacity is well worth the price increase (assuming you can afford it).

#13 blueman

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Posted 26 February 2009 - 12:22 AM

Hi,
I have replaced both gearboxes and installed the Ovision Worm and Block as well.
The PE is now about +- 2.3" or 4.5" peak to peak uncorrected and is pretty smooth too.
Total cost was about $600 with shipping and all, for everything on the upgrades.
The Ovision Worm is a much better worm and the worm block is quite good too and made with stainless steel.
Blueman (Floyd)

#14 blueman

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Posted 26 February 2009 - 12:26 AM

Hi Jarad,
How do you like the VC200L?
Blueman

#15 Strgazr27

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Posted 26 February 2009 - 08:16 AM

My new to me G11 showed up this past Friday replacing my EQ6. Thanks to Joe B. for an incredible trade. The mount was in better condition than he stated and looks brand new :) As usual the performance of the RA clutch was basically non existant. As you know I can't keep my hands out of anything so I tore it completely apart and rebuilt the mount. Not only was it incredibly easy to work on but I'm more than happy with the results. While I had it apart everything was cleaned and relubed. I also spent about 5 hours polishing the RA worm and ring gear. I setup a jig to hold an electric drill and let her run. I would wipe down and apply new polishing compound every 30 minutes and make a minor adjustment to the worm position. Not having $500 to spend on the Ovision block I used the stock block cover to make a support to hold the worm blocks square to each other. I'll have pictures up in a little while. The Pempro run below was with 32 lbs of equipment on the mount using a piggyback setup. As it still shows the 76 second error I have some adjusting to do. The magnitude doesn't look that bad so I wunder if it's going to be a big issue? Most of my imaging is under 1000mm. I have also ordered a set of ABEC7 replacement bearings for the worms from a link Floyd posted (Thanks Floyd!). I was not able to get any images after the run as clouds cut short even the PE trials but I'm pretty happy with the results. I am planning to do the gearbox mod next. At under 2 arc seconds peak to peak uncorrected I think I'm going to be happy ;)

Here are a few screen shots from the run. Larger images can be seen

Here

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#16 Strgazr27

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Posted 26 February 2009 - 08:24 AM

One more...

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#17 waassaabee

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Posted 26 February 2009 - 10:25 AM

All of this talk about upgrades, modifications, 76 second error, concerns me a bit. How are they 'out of the box'? Brand new? Or maybe look for one someone has tinkered with?

#18 Jared

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Posted 26 February 2009 - 12:08 PM

Hi Jarad,
How do you like the VC200L?
Blueman


For the price, it's an excellent imaging scope. As advertised, it has a flat field right to the corners of a 42mm imaging circle. My sample has some slight astigmatism that is noticeable only at high powers when used visually. The focuser is pretty good, but isn't quite as beefy as I would like for my relatively heavy SBIG STL series camera. Still, it seems to work fine. Biggest gripe is that the relatively thick spider vanes cause somewhat blocky star images.

If you are looking for a long focal length imaging scope in this aperture range that can handle a full frame CCD chip, there really isn't anything else that's close.

#19 Strgazr27

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Posted 26 February 2009 - 01:28 PM

If you are looking for a long focal length imaging scope in this aperture range that can handle a full frame CCD chip, there really isn't anything else that's close.


Actually the AT 8RC will easily do it, features a Feathertouch focuser, fully baffled tube and normal spider vanes. Oh yeah and it's almost $500 cheaper ;)

#20 rsbfoto

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Posted 26 February 2009 - 01:37 PM

All of this talk about upgrades, modifications, 76 second error, concerns me a bit. How are they 'out of the box'? Brand new? Or maybe look for one someone has tinkered with?


Hi,

It is like with new cars. You can get a good one but you can also get a lemon :cool: and you can get the standard between these 2 stages which is by far more common. If you get a good one you will only know it after a few months you have used it. If you have a bad one too.

A good one I would say has a PE of +-3", a standard one has maybe +-4to7" and a bad one more then +-10". With the new brass worm after maybe a month of continous use the PE will surely settle down on a value an then you can say what you have got. My 2 cents to the PE ...

When I got my first G11 the only thing I did in the first 6 months is to learn how to use it and that was it. Nothing else. I did not even touch the worm/gear mesh just because I did not know how to do it correctly. After knowing how th mount works I spend another time month after month just using it and doing visual as well as imaging and when I finally felt confident about the mount I started to tinker woth the mount.

That is what I can say in regard to your question.

#21 blueman

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Posted 26 February 2009 - 03:54 PM

I heard the AT RC8 will no longer feature (or offer) the Feathertouch and that they can not say a Feathertouch will even fit the scope. It seems to be the same focuser that the 6" uses and it will not handle a 3 lb camera, according to Astro-Tech. So, not sure what to say about the 8" model, may not be good for cameras like my ST2000xm with filter wheel.
Cost $1395
Blueman

#22 blueman

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Posted 26 February 2009 - 03:57 PM

Hi,
This looks very good indeed. If you can get the two blocks to line up without causing the two bearings to bind, the 76 error will diminish a lot.
I am not sure what it is saying the actual Peak to Peak is, but it looks smooth enough.
Blueman

#23 alanon

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Posted 26 February 2009 - 04:46 PM

So with all of the need to rebuild, and The GM-8's performance being so average at a medium load capacity, what is the advantage to paying such a premium for this rather light weight mount? An Atlas is cheaper, and a Sirius has as good a capacity. What DO you get from a GM-8 that justifies the cost? I looks great, but that in itself doesn't seem to warant the $1000 premium. For a thousand or more dollars over the 2 Orion offerings wouldn't one expect a premium performance? What am I missing here?

#24 Strgazr27

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Posted 26 February 2009 - 05:13 PM

I heard the AT RC8 will no longer feature (or offer) the Feathertouch and that they can not say a Feathertouch will even fit the scope. It seems to be the same focuser that the 6" uses and it will not handle a 3 lb camera, according to Astro-Tech. So, not sure what to say about the 8" model, may not be good for cameras like my ST2000xm with filter wheel.
Cost $1395
Blueman


Floyd,

As of today the Feathertouch will be offered as an option with the adapter for $450 on top of the base price of $1395. There are no issue with fit of the FT. I don't know who gave you that information but it's incorrect. Both the 6 and the 8 are going to use a newer style focuser that uses a rail and bearing system and will easily support more than 3 lbs ;) and should be good to at least the 8lb mark. The optics will easily cover an APS-C chip and will do a FF with perhaps the need for flat frames. There is plans for a .75 reducer for the scope also.

I have attached a picture of the new focuser which shows the new design. There are 4 bearings that guide/support the drawtube and should work very well.

I do stand corrected though. With the FT focuser the price difference is basically a wash between the VC and the ATRC. The baffled tube and FT focuser are a big step up from the VC's as well as the AT having a normal set of spider vanes.

Hope this info helps clear things up a bit :waytogo:

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#25 waassaabee

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Posted 26 February 2009 - 05:25 PM

Back on subject here...

Dan, I'm with you.. Maybe that CGEM isn't such a bad deal after all...






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