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Alt-Az vs. GEM mounts for SCT scope

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#1 Nocturnal

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Posted 04 October 2005 - 12:58 PM

All,

I currently have a Meade DS2090 refractor and a Super C8+ on loan. Eventually I'll want to buy my own 'big' scope so I'm trying to familiarize myself with the advantages of various configurations. I noticed that you can buy larger SCTs if you buy them with a GEM vs. an Alt-Az mount. In both cases I'm referring to Goto equiped scopes like the Celestron Advanced C11-SGT compared to say a Meade LX-90.

I haven't picked apart the feature lists in great detail yet but it appears that Alt-Az fork mounts carry a premium over GEMs. Is this true? If so, why is this? I thought both mounts have their advantages and neither was 'better' than the other. In fact it seems that a GEM is harder to make than a fork but what do I know :)

Thanks for any insights you may have.

Sander

#2 jrcrilly

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Posted 04 October 2005 - 02:23 PM

I haven't picked apart the feature lists in great detail yet but it appears that Alt-Az fork mounts carry a premium over GEMs. Is this true?


No, it's not. For comparable quality and capacity you should expect to pay a substantial premium for a GEM. If you are looking to compare imported mounts such as the LXD75 or the CG5-GT you must consider that neither Meade nor Celestron offers a comparable forkmount. Meade's entry level forkmount is the LX90, which is a domestic product - and which can be used to hold a 50 pound 12" SCT. It's not appropriate to compare that to any of the imported Vixen clones. The only GEM being currently produced (rather than imported) by either Meade or Celestron is the CGE. It's in the same quality/capacity class as the LX200GPS and the Nexstar GPS series forkmounts - but costs substantially more than either. Meade's former LXD750 GEM was in that class also, but was more expensive yet.

For general visual use the forkmounted SCT's are faster to set up and more comfortable to use. Before moving up to a comparable GEM one should be sure that the features of a GEM are worth the reduced convenience and increased price to that particular user. For general imaging a good-quality GEM tends to be a better bet.

On the other hand, there's nothing at all in the price class of the clone GEMs so the decision to choose one of those would be based primarily on weight, versatility, or economy - but one shouldn't expect the performance to match any of the current forkmounted models except perhaps the ultralight NXi series.

#3 TK6411

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Posted 04 October 2005 - 02:43 PM

Nocturnal,

John is correct that the best GEMS are heavier duty units than the Synta clones of the Vixen mount but don't think that either the LXD75 or the CG5 aren't decent GEM's ...bottom line they are. While I wouldn't put a 10" or larger SCT or SN on a LXD75 or CG5 mount I have no problem with using the LXD75 for my 8" SCT or even the 8" SN OTA...both visually or for astrophotography. I found that I won't go back to fork mounted scopes after using the LXD75. A decent heavier duty GEM is the Orion Atlas...now with GOTO. Not a bad deal and can handle the 11 SCT very well.

Jim

#4 jrcrilly

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Posted 04 October 2005 - 02:55 PM

don't think that either the LXD75 or the CG5 aren't decent GEM's ...bottom line they are.


Hi, Jim.

Sure; I've owned the Meade and Celestron offerings (and an Atlas) and all worked well for me. I usually keep an lXD55 or 75 around for field use because of the versatility. I just wanted to be sure the poster understands that within a given class a GEM will be more expensive than a forkmount rather than less.

#5 NorthCoast

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Posted 04 October 2005 - 03:38 PM

I have both Meade 8" LX-90 SCT fork-mounted and a Meade 8" SCT on an Orion SVP GEM. I have found that the two mounts offer different advantages and features.

But first, the LX-90 for the GOTO, mount and scope was about the same cost as the SVP without GOTO. (Both scope have UHTC so coating were not a factor). This supports John's statement.

1) I find that setup of the alt-az is much quicker.
2) I find that the GEM mount can be used with other gear (e.g. small scope, borrowing from friends, etc.)
3) I find that the GEM can be more easily balanced when added/removing accessories (e.g. camera, bino viewers, larger EPs, etc.) especially within the same viewing session.
4) I find that the alt-az does not easily facilitate "manual" operation. The GEM does and can be run more easily without electricity.
5) I find that one can place more equipement in the optical train with a GEM. Attaching gear to the back of an fork mounted SCT may limit the range of motion (e.g. viewing at/near zenith)
6) Fork mount is more comfortable to view because of EP location
7) Fork mounts have less parts to forget at home and take up less space when trasporting! :)
8) In my case the fork mounted SCT has better dampening time. This could just be the setup of the GEM, or the mount legs, but, I feel that the forks are also contibuting to it being more ridged.

No functional:
9) I started with a alt-az fork mounted ETX, so....
10) Fork mounts look cool!

I use both. I like the LX-90 better for visual. The SVP mount has let me use/try a number of other scopes "on lone" and with my WO 80mm refractor. Can't say that I would trade them all in for a single premium GEM, but the LXD 750 and LXD 650 sales at the Meade outlet had me close on more tham a few times recently...

Later,
Mark

#6 Nocturnal

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Posted 04 October 2005 - 04:00 PM

I've done some quicky lookups on scope prices at OPT (prices are the same everywhere anyway it seems).

All scopes have advanced coatings and have 8" apertures.

GEMs:
C8-SGT $1514
SC-8AT LXD75 $1574

Forks:
C 8i SE $1400
CPC 800 $1999
LX90-8 $1974

Orion doesn't list an 8" goto scope yet.

The LX has LNT which is nice but other than that the scopes are reasonably equal in terms of features. So based on your replies it appears the price difference is based on the cheapness of the GEM mounts which are imported. This is of course also reflected in the 8i which has a simpler alt-az mount than the other ones.

What remains is the question of quality/features. As usual 'you get what you pay for' probably holds. At the same time GEMs are more suitable for astro photography that forks until you add a wedge to the setup which makes it even more $$. How would you quantify the quality difference between a domestic fork and an imported GEM? Given the quality of domestic (US) cars I'm not sure the 'domestic' part is such a great selling point from a quality perspective :-)


I actually think a fork makes for more intuitive navigation for visual exploration because up is always up and east is always east. My C8 on a wedge is more difficult to manouver because the angles change. At least it's more difficult for me :-)

Thanks for your replies and insights.

#7 Nocturnal

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Posted 04 October 2005 - 04:02 PM

Thanks Mark for your reply. Great summary of advantages on both types of mounts.

#8 southmike

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Posted 04 October 2005 - 04:18 PM

I would never think of using a c-11 on a mount like the asgt(cg5)...but my line of thought of use also goes, to using it for imaging. the sky watch eq6/orion atlas6 with goto seems to be the best value, for big ota's.

I think 8~9 inch ota's are the sweet spot for portability. and stability. some imaging can be done with asgt-and lxd55~75's but they are just not as smooth as the more then triple priced g11, and cge. (the g8 would be a good fit)

the one nice advantage of an eq mount is it breaks down farther..into lighter weight components..(the eq head can still be kinda heavy though) ........ but forks are
nice because they won't bang into the tripod at zenith.
and come as 2 basic sections, 3 if it is wedged.

now if visual only is your thing i would go with a nexstar 8
or a asgt8,lx75-8. lighter then lx90's or lx200/nexstar gps.

Personally I have found the alt/az fork mount to be easier to learn, and track manually then an eq mount....once it is wedged though the motions are similar. I also feel it is easier to move my lx200 8 then it is to move the 102ed on the lxd650.


If i was to be forced to rank them in order of purchase preference..
i would say CGE/g11 gemini 9.25, ,gm8 -8, lx200/gps 8, lx75/asgt 8.. the kicker is the atlas..I am not sure how good of an imager it is, to put it in front or behind the lx200's.

#9 jrcrilly

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Posted 04 October 2005 - 04:29 PM

How would you quantify the quality difference between a domestic fork and an imported GEM?


Setting aside the Nexstar series, which sacrifices performance for extreme portability, the domestic forks work very well - in the same performance class as the CGE. Uncorrected PE of less than +-15 arcseconds, easily correctable to less than +-5 arcseconds is usual. I've never attempted to image with a clone mount, but if they were delivering numbers like that we'd be hearing about it.

I've been inside many clone mounts getting them to work properly, but although I've owned many more forkmounts, I've never had to get inside a single one. GEMs of comparable quality and performance exist - but they'll cost you.

#10 jrcrilly

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Posted 04 October 2005 - 04:33 PM

Forks:
C 8i SE $1400
CPC 800 $1999
LX90-8 $1974


Leaving the ultralight NXi out of the mix, you are neglecting to list the GEMs that are comparable to those forkmounts. Turns out that from Meade and Celestron there's only one; the CGE800 at $3650.

#11 snorkler

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Posted 05 October 2005 - 01:05 AM

Sander,

If you're considering astrophotography with your future scope, you have to add the price of a decent aftermarket wedge (a Mitty, Milborn, etc - NOT a Meade) to get a fork mount capable of imaging. Once you add that $500 into the picture, a used SCT on a Losmandy G-11 EQ mount costs about the same or less as a used fork mount system.

#12 Nocturnal

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Posted 05 October 2005 - 12:18 PM

Darrell,

note I wrote this above "At the same time GEMs are more suitable for astro photography that forks until you add a wedge to the setup which makes it even more $$" so I had taken that into consideration :-)

Benefit would be that a wedge could be added later, spreading the sticker shock a little. $500 For a wedge? Djeez.

Sander

#13 Nocturnal

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Posted 05 October 2005 - 12:33 PM

John,

That CGE800 almost looks weird. Tiny scope on huge tripod. The darn thing weighs 100 Lbs! I guess that's how they get you to buy that big 14" mortar :-) "Honey you know I can't show up with a scope that looks that deformed, I -have- to get the 1400" :-)

Sander

#14 jrcrilly

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Posted 05 October 2005 - 01:23 PM

John,

That CGE800 almost looks weird. Tiny scope on huge tripod. The darn thing weighs 100 Lbs! I guess that's how they get you to buy that big 14" mortar :-) "Honey you know I can't show up with a scope that looks that deformed, I -have- to get the 1400" :-)

Sander


Yes, it looks like a brute - but there you have the difference between a forkmount and a GEM. It takes a GEM that substantial to match the stability of the NX8GPS forkmount model (except maybe the tripod is a little bit overkill - and except that it probably STILL isn't quite as rock-solid as the NX8GPS).

The CGE will handle the 14" tube reasonably well (well enough to fulfill the needs of some folks) but the performance won't be as good as when loaded with the 8".

If I go back to a big SCT I'll probably go back to a forkmount.

#15 Mike B

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Posted 05 October 2005 - 04:24 PM

John-
I see where Orion has their 'Celestron'-made 8" & 9.25" SCTs offered on their "SVP" EQ mount. Where are these SVP mounts in the spectrum of things (they're rated at 20# capacity) like LXD & CGE mounts? Not being an "imager", will that SVP mount work for visual use with the Orion/Celestron 9.25" SCT?... or is too much of a stretch? What are your thots?
Thanks,
:cool:mike b

#16 Digital Don

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Posted 05 October 2005 - 04:57 PM

Hi Sander,

The major benefit of an Alt-Az fork mount is stability. The exact same scope tilted over on a wedge will not seem nearly as solid. Also, the system will be lighter than the same tube mounted on a German mount because no counterweights are required.

The main benefit of a German mount is perhaps versatility. With the common dovetail mounting systems available today, almost any optical tube can be placed on any mount. However as John mentioned, a substantial German mount is required for even a moderate size tube assembly if stability (or imaging) is your primary concern.

Neither one is 'best'. As you mention, each type has its own good and bad points. The 'appropriate' mount depends on what scope will be attached to it, and whether its intended as a visual or photographic platform.

Don :usa:

#17 jrcrilly

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Posted 05 October 2005 - 05:42 PM

John-
I see where Orion has their 'Celestron'-made 8" & 9.25" SCTs offered on their "SVP" EQ mount. Where are these SVP mounts in the spectrum of things (they're rated at 20# capacity) like LXD & CGE mounts? Not being an "imager", will that SVP mount work for visual use with the Orion/Celestron 9.25" SCT?... or is too much of a stretch? What are your thots?
Thanks,
:cool:mike b


For a few years Celestron offered the C8 and C9.25 bundled with a GEM similar to the SVP but with a much weaker tripod. The current SVP would be better than that setup - and C seemed to think it was OK. There were complaints about the C9.25 on that mount so C started to bundle it with a GM-8 (they called the package the GM-9). I wouldn't be afraid to try it visually with an SVP. It's nearly in the same class as the CG5-GT and the LXD75.

#18 Mike B

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Posted 05 October 2005 - 06:57 PM

Thanks John- that makes sense. :grin:

#19 NorthCoast

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Posted 06 October 2005 - 08:24 AM

John-
I see where Orion has their 'Celestron'-made 8" & 9.25" SCTs offered on their "SVP" EQ mount. Where are these SVP mounts in the spectrum of things (they're rated at 20# capacity) like LXD & CGE mounts? Not being an "imager", will that SVP mount work for visual use with the Orion/Celestron 9.25" SCT?... or is too much of a stretch? What are your thots?
Thanks,
:cool:mike b


For a few years Celestron offered the C8 and C9.25 bundled with a GEM similar to the SVP but with a much weaker tripod. The current SVP would be better than that setup - and C seemed to think it was OK. There were complaints about the C9.25 on that mount so C started to bundle it with a GM-8 (they called the package the GM-9). I wouldn't be afraid to try it visually with an SVP. It's nearly in the same class as the CG5-GT and the LXD75.


As stated above I have identical OTAs both on the Orion SVP and the LX-90. Both are very good visually, however, I give the LX-90 mount the edge. I have also used the LXD-75 next to the SVP and they are in the same class...

Mark

#20 jrcrilly

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Posted 06 October 2005 - 12:03 PM

As stated above I have identical OTAs both on the Orion SVP and the LX-90. Both are very good visually, however, I give the LX-90 mount the edge. I have also used the LXD-75 next to the SVP and they are in the same class...

Mark


Hi, Mark.

Yes, it'll take a more substantial mount to keep up with a forkmount. I suppose I was being picky when I described the SVP as nearly in the same class as the CG5-GT and LXD75. It has similar castings; it's just a little lighter in the bearings and tripod. Let's call it the light end of the same class!

#21 Mike B

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Posted 06 October 2005 - 12:26 PM

"...it's just a little lighter in the bearings and tripod"

John-
The SVP tripod is like 2" chrome-steel legs... looks very much like my Meade LX50 tripod! Are the tripods for the CG5-GT and LXD75 heftier than that?... or are you speaking of the tripod "head" & bearings?

Am glad to hear your & Mark's reports as to the visual serviceability of the SVP... i'm thinkin' the 65# of my 10" SCT base/fork/OTA assembly is a real clunk to haul around- the thot of moving to the 20# 9.25" OTA is a very comforting one! And i'm seriously considering it, as with their "advanced" coatings (probably NOT an *Orion* unit, but an actual *Celestron* one) it oughta be in the same league photon-wise... maybe even with an upward bump in overall optical quality. My aching back will certainly appreciate it! :ubetcha:
:cool: mike b

#22 jrcrilly

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Posted 06 October 2005 - 12:32 PM

The SVP tripod is like 2" chrome-steel legs... looks very much like my Meade LX50 tripod! Are the tripods for the CG5-GT and LXD75 heftier than that?


Hi, Mike.

No, 2" would match the others. Sorry; it's hard to keep up with these things - I guess they've beefed them up since the last SVP I saw. I'll have to make sure I'm current before posting comments like that.

#23 southmike

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Posted 06 October 2005 - 01:31 PM

the lxd750 is huge, most of its size is tripod.
..extended it is probably close to the ceiling.
it is a a version of meades giant tripod.

#24 jrcrilly

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Posted 06 October 2005 - 02:00 PM

the lxd750 is huge, most of its size is tripod.
..extended it is probably close to the ceiling.
it is a a version of meades giant tripod.


It is the original, full-height (40" min, 50" max) Giant Field Tripod. The only difference between it and the original GFT supplied with the LX200 is the color; the castings are gray instead of black.

I don't remember how the LXD650 head mounts, but the LXD750 head has a flat bottom plate and accepts the same 1/2" X 13tpi center thread as an LX200 so it'll sit on the tripod or a pier just as the LX200 does.

#25 NorthCoast

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Posted 06 October 2005 - 02:34 PM

As stated above I have identical OTAs both on the Orion SVP and the LX-90. Both are very good visually, however, I give the LX-90 mount the edge. I have also used the LXD-75 next to the SVP and they are in the same class...

Mark


Hi, Mark.

Yes, it'll take a more substantial mount to keep up with a forkmount. I suppose I was being picky when I described the SVP as nearly in the same class as the CG5-GT and LXD75. It has similar castings; it's just a little lighter in the bearings and tripod. Let's call it the light end of the same class!


We agree. :)

Later,
Mark


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