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6" f/15 on a G11?

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#1 polaraligned

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Posted 16 May 2009 - 10:11 AM

The G11 will easily handle the weight, I am worried about
the moment arm and shaking because of the long tube.
Anyone experience using such a long tube on a G11?

Thank You,
Scott

#2 bluestar

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Posted 16 May 2009 - 10:45 AM

This is my current 6" f/15 on the previous owner's G-11. It works BUT the feeling between us was that the moment arm (i.e. tube torque) was a bit much leading to excessive tube jiggles. Said ota came with a motofocus which helped a LOT...i.e. the less you have to manipulate/touch the tube the better.

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#3 bluestar

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Posted 16 May 2009 - 10:58 AM

http://www.jimsmobile.com/

...sells motofocus for contemporary AP focusers, which D&G uses. They also sold motofocus units for vintage D&G focusers. Now discontinued they MAY still have some in stock for older telescope units. Sell focus motors for many other brands as well.

#4 mconnelley

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Posted 16 May 2009 - 03:00 PM

Hello:

I have a 144 mm f/14.5 doublet mounted on my G-11, and I think it works fine. The long moment arm of the tube is noticeable. For example, putting a heavy eyepiece feels a bit more bouncy with the refractor that with my Cassegrain. However, I don't think that the images jiggle that much, and certainly aren't a problem as long as it's not too windy. I did try to make the scope light, and I've done a bit of tweaking to the G-11 itself. On the G-11, I've adjusted the worm mesh to minimize backlash, and replaced the nylon clutch pads with teflon so that I can smoothly move the scope with the clutch knobs fully tightened down.

Cheers
Mike Connelley

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#5 polaraligned

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Posted 17 May 2009 - 05:42 AM

Thank You guys. It looks like I am going to get the used
G11 that is available to me.

Bluestar- It looks like there is a height extension on that tripod. Is that a losmandy product?

Mike- That is a great idea with the teflon. I will have to do that.

#6 bluestar

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Posted 17 May 2009 - 08:12 AM

Yes, I don't know the part # but it IS the Losmandy G-11 Pier Extension. Here's one I used for my 5" f/12....

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#7 Joe Bergeron

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Posted 17 May 2009 - 11:43 PM

My 6" f/9 is acceptable, but marginal, for visual use on my G11. A nearby observatory has a 6" f/12 on one...not very stable. An f/15? Don't go there.

#8 polaraligned

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Posted 18 May 2009 - 07:57 AM

Alright. I just killed my G11 deal.
What do you guys think of a Discmount 6?

#9 Scott99

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Posted 18 May 2009 - 10:00 AM

D&G does say G11 is OK w/ that scope, maybe with all the long tubes they have greater tolerance of the shakes:

http://www.dgoptical.com/faq.htm

#10 Joe Bergeron

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Posted 18 May 2009 - 10:26 AM

D&G does say G11 is OK w/ that scope, maybe with all the long tubes they have greater tolerance of the shakes:

http://www.dgoptical.com/faq.htm


Yeah, they probably do. I can see why they would suggest the G11, as it's probably the only reasonably priced mount you can get which would be remotely usable with a 6" f/15. In my opinion, nothing less than an A-P 900 or 1200 would really be adequate for such a scope. Any mount for an 8' long scope would have to be super tall too, of course.

#11 rwiederrich

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Posted 18 May 2009 - 10:52 AM

Yes, I don't know the part # but it IS the Losmandy G-11 Pier Extension. Here's one I used for my 5" f/12....


Great scope!

Where in the world have you been :question: :foreheadslap:

Rob

#12 CHASLX200

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Posted 18 May 2009 - 11:56 AM

My G-11 did a pretty good job of holding my 6" f/9 AP. I used the Meade giant field tripod with the G-11. The long tube of a 6" f/15 could be pushing it a little.

Chas

#13 bobhen

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Posted 18 May 2009 - 01:56 PM

You might try a Hargreaves strut - google "images' for some pics.

I never used one but there was an article in Sky & Telescope a few years ago where the author (Thomas Dobbins) had a C14 and 4” refractor on a G11 and with the strut the improvement was such that he saw no need to upgrade the mount – it’s looks like a somewhat easy add-on.

Bob

#14 Bob Myler

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Posted 18 May 2009 - 02:15 PM

Torque from long OTA's can often be minimized with the use of a hargreaves strut: simply a half-inch hollow aluminum tube connecting - with the use of clamps - one end of a GEM's (rotating) dec axis, and the other end to the OTA at a point right behind its objective cell. Small universal joints are needed to get the hypotenuse angle just right - the longer the better. S&T had a write up on this fix a few years ago, complete with materials list...

#15 mclewis1

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Posted 18 May 2009 - 06:26 PM

I'll second (er third) the Hargreaves strut concept ... that and a good long Losmandy D plate with nice solid rings. With those types of upgrades you might have a shot at an acceptable setup.

#16 Steve Fisher

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Posted 18 May 2009 - 09:47 PM

The fellow I purchased my 6" f/12 from sold it to me because he hated how wobbly it was on his G-11. The first time I mounted it on my CGE I couldn't stand how much time it took to settle down during focus.

Making a Hargreaves strut from 1/4" threaded rod made all the difference in the world.

Without fail every time I take it out in public someone comments on how stable it is.

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#17 Steve Fisher

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Posted 18 May 2009 - 09:48 PM

Here is all it takes.

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#18 polaraligned

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Posted 19 May 2009 - 08:24 AM

Thanks Steve and everyone.
The strut is a clever idea.
Question is- will I be happy with a strutted G11.....

Scott

#19 GShaffer

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Posted 19 May 2009 - 12:46 PM

I would say that is entirely dependant on how much empty pockets weigh in to your happiness. When you climb above the G11 looking for greater capacity money starts flowing out of your pockets at an expotential rate :)

#20 Steve Fisher

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Posted 19 May 2009 - 08:33 PM

Thanks Steve and everyone.
The strut is a clever idea.
Question is- will I be happy with a strutted G11.....

Scott


Scott:

I would say "yes" I think I could live with a G-11 for visual use. If you plan AP I would say "no way".

The strut is more than a clever idea, it is amazing! :jump:

#21 watcher

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Posted 20 May 2009 - 01:44 AM

Or you can go for one of these mounts. Cheap high capacity mounts

Joe

#22 bluestar

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Posted 20 May 2009 - 06:30 AM

Yes, I don't know the part # but it IS the Losmandy G-11 Pier Extension. Here's one I used for my 5" f/12....


Great scope!

Where in the world have you been :question: :foreheadslap:

Rob


Internet's taken a back seat these days ...
- my cancer surgeries and followup
- my wife surgery overlapping plus other medical concerns for us both
- passing of mom and dad, plus wife's mom last week in addition to three other close family/good friends
- huge gov't employer Departmental reorganization/reshuffle and traumatic shop relocation
- learning new stay-alive lifestyle regimen
- purchasing a pop-up camper and hitting the road for stargazing and fishing :gnottagnome:
- attending NEAF for the first time and for the entire event, not just conduct business in the parking lot
- bought some more cool astro gear for BlueStar; probable purchase lead for an 8" f/12 D&G for us in Florida (pickup?)
- rediscovering value of life and appreciating every day we have on this earth as precious and to be lived to the fullest :praying:

That hits the highlights... :rainbow:

#23 bluestar

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Posted 20 May 2009 - 07:31 AM

I would say that is entirely dependant on how much empty pockets weigh in to your happiness. When you climb above the G11 looking for greater capacity money starts flowing out of your pockets at an expotential rate :)


New G-11 running 2-3K depending if you want goto; used in the mid ~1K
My used AP800 cost ~1500; I had several offered to me
My used AP1200 HDA cost $3200; I had several early vintage avail to me in past 12 months
My used Parsec/12 cost ~$1800 ish if I remember correctly
I've had several AP900 QMD offered to me ~$3.5K ish range

They do take extra umph and payload capacity to mount decently, but with some systematic searching you CAN come away with some sleeper STEALS of high quality high mount capacity w/relatively inexpensive cost and an ota/mount complete rig for the same or less than just an APO ota. Older, simpler (vintage) mounts ARE becoming harder to come by, as evidenced by some of us CN'ers scouring the 'net and AM are discovering; some sellers of these have a hard time moving them because everyone wants goto. Take D&G's list of mounts and start want ads for these...you MAY be surprised how many people have some sitting around unused for some quick cash. Schaefer-mounts (with updating electronic mods) figure prominently @ D&G's/friends observatory complex, those refurbished Schaefer mounts on AM get snatched up pretty fast so there's some of us out there that know a good thing when we see it.

These classic-designed optical knuckle-dragger scopes remain nichy (and always will) and as Steve demonstrates you CAN mount these long focus scopes reliably and for lots of visual fun at decent cost. A G-11 with a pier extension, motofocus, hargraves strut and possibly sliding tube counterweight set would IMHO make a VERY substantial and satisfying visual setup. Maybe someone could throw together and sell an aftermarket hargraves kit with basic parts and rings...maybe make a few bucks on the side and help out fellow knuckle-draggers down on their luck.

Mikey's "it's not big it's large" mount for his 8" f/13.3 is a beefed-up copy of basic mounts by Opticraft. They aren't sleek and pretty (though Mickey's has a sublime beauty of its own), I wouldn't discount these one bit. I was VERY close to going the Opricraft route till I came upon some used mounts at opportune moments.

#24 mikey cee

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Posted 20 May 2009 - 09:47 AM

Mikey here.....Yes sireee Pat I can't believe some don't go this route. They are not that difficult to make if you are handy or have access to a buddy with a machine shop. Too many would rather trhrow big bucks at a "pretty" mount. You don't see many mounts in pro observatories that look "pretty". They are utile and functional firstmost. Sometimes you will pay(headaches) for the right to have your cake and eat it to! Me I didn't want any headaches and breakdowns....just real "solid" performance! When you get into large long focus refractors I can't help if it offends some. That's just the nature of the beast if you will.:smirk: :grin:Mike

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#25 mikey cee

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Posted 20 May 2009 - 09:55 AM

There just is no room for errors on this type of mount...especially when using self aligning pillow block bearings. No flex and no play...industrial strength! Sorry but "everthing" has a tradeoff point in life and this is no exception.:grin:Mike

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