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Vixen GP-DX with refractor

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#1 dweller25

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Posted 08 July 2009 - 02:08 PM

Hello,

I currently mount a 4" F/8 refractor on my Vixen GP-DX. The combination is very solid.

Is anyone using a 5" plus refractor on this mount and if so which scope and how stable is it ??

#2 jrcrilly

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Posted 08 July 2009 - 02:14 PM

Is anyone using a 5" plus refractor on this mount and if so which scope and how stable is it ??


The mount does a fine job with an FS-128.

#3 GShaffer

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Posted 08 July 2009 - 03:21 PM

I have a GPDX with a wooden tripod that I regularly use a 5.5" OTA on and occasionally a 6" and it handles either just fine......

#4 tim53

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Posted 08 July 2009 - 04:24 PM

I used to mount my 6" Jaegers f/10 on a Super Polaris mount. It worked, but it's beyond the upper limit for that mount. Probably similar for a GPDX.

I would think a 5" would be okay, though, depending on focal length.

-Tim.

#5 GShaffer

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Posted 08 July 2009 - 08:39 PM

Well the 6" I have is an F/8 and I wouldnt try imaging with it on the GPDX but it is quite acceptable for visual.....the 5.5" is only a F/5.7 and very light for its size, about 11 lbs naked.....close to rock solid with it.

Bottom line it should handle a 5" nicely as long as we arent talking about something like the long D&G OTA's

Greg

I used to mount my 6" Jaegers f/10 on a Super Polaris mount. It worked, but it's beyond the upper limit for that mount. Probably similar for a GPDX.

I would think a 5" would be okay, though, depending on focal length.

-Tim.



#6 Jeff B

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Posted 08 July 2009 - 10:42 PM

I'm using an older AP 130 F8 and F6 with my plain old GP and SP's and they work fine for visual use as long as you pay attention to balance and choose a good tripod. The stock tripod is the limiting feature for me.

Jeff

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#7 dweller25

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Posted 09 July 2009 - 02:41 AM

Thanks for all the replies, 5" F/8 sounds like a safe bet.

#8 BarrySimon615

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Posted 09 July 2009 - 08:50 AM

5" f/8 may be a safe bet for visual use with a fairly light weight tube but not for astrophotography.

I have both a standard Celestron Super Polaris mount and also a Vixen Super Polaris DX mount. The DX version has about a 5 lb additional payload capacity, maybe 3 lbs more for astrophotography. Based upon my experience with both mounts with scopes ranging from an 80 mm f/11 to a 94 mm f/7 (Brandon apo) to a Celestron 102 mm f/9.8, to a TAK TSA 102 and finally a Jaegers 6" f/5, I would say the following:

all work well enough for visual on the regular Super Polaris which I would give a visual payload capacity of about 22 lbs, and a photographic payload capacity of about 17 to 18 lbs. The Super Polaris DX would have a visual payload capacity of about 27 lbs, perhaps a lb. or 2 more; and a photographic payload capacity of about 23 to 24 lbs. This assumes everything is properly tightened, the tripod is collapsed as much as possible and there is no more than a light wind. I would assume that the GP-DX should be pretty much equivalent to the SP-DX with both mounts being fairly equivalent to the Losmandy G8 from my experience with that mount.

Barry Simon

#9 jrcrilly

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Posted 09 July 2009 - 08:56 AM

I would assume that the GP-DX should be pretty much equivalent to the SP-DX with both mounts being fairly equivalent to the Losmandy G8 from my experience with that mount.

Barry Simon


Hi, Barry.

The stock Vixen tripod probably does bring it down to GM-8 class. I should probably have mentioned earlier that my GP/DX is on a beefier steel tripod. I wouldn't hesitate to image with the FS-128 on it.

#10 Jeff B

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Posted 09 July 2009 - 08:39 PM

I agree that getting the max performance out of the SPs and GP/GP DX demands a better than stock tripod. I've had very good success using a Meade LXD 75 with both mounts. Payload capability and damping times are noticably improved.

But I have to differ regarding the Losmandy GM8. From my use, it's a solid notch or so above the SP/GP/GP-DX.

Jeff

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#11 Jeff B

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Posted 09 July 2009 - 08:45 PM

The GM8 did a very good job of even supporting my AP 152 F9.

Jeff

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#12 Jeff B

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Posted 09 July 2009 - 08:47 PM

And my Jaegers 6" F10. I've no experience with imaging.

Jeff

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#13 gnowellsct

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Posted 09 July 2009 - 10:37 PM

The SP-DX is a bit heftier than the GP-DX and if you can find one used is a viable option. Nice mount. regards Greg N

#14 BarrySimon615

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Posted 09 July 2009 - 10:47 PM

With mounts like any of the GP, GP-DX, SP, SP-DX or Losmandy G8, the issue with scopes approaching their payload capacity for either visual or photographic applications is weight plus moment arm issues when the tube is both relatively heavy and long. A Super Polaris does great with a Celestron 80, but slightly less well with a Celestron 102 f/9.8 (but still perfectly fine). However if you mount a 6" f/8 reflector on one you will see some noticeable moment arm problems. Keep in mind that such a tube is longer and a bit heavier. With a 6" f/8 reflector mounted on a Losmandy G8 I find the wobble introduced with this tube assembly, which is well under the 30 lb. specified payload limit to be unacceptably excessive. In another thread the discussion turned to the need to keep movement as seen thru the eyepiece at 2 seconds or less and certainly no more than 2.5 seconds when a fairly sharp slap is applied to the tripod. I would be very curious to know how long it takes the telescopes pictured above to settle down with this test. If that long or longer for visual use it may be just an annoyance, if astrophotography is contemplated it would be a very serious challenge.

Note - I had a Brandon 130 f/8 with various guidescopes mounted on a Losmandy G11; the payload weight was 33 lbs. It also had 31 lbs. of counterweight and the vibration settle down time was about at the 1.5 second range. I felt that this combination was good, but I felt that I was close to the limit. I believe a 40 lb. payload with a tube like the Brandon 130 length would have been too much for anything beyond casual visual use.

Here is a picture of the Brandon 130/Losmandy G11 setup that I had.

Barry Simon

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#15 jason_milani

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Posted 10 July 2009 - 09:17 AM

The SP-DX is a bit heftier than the GP-DX and if you can find one used is a viable option. Nice mount. regards Greg N


I don't think so. The GP (Great Polaris) is (was) a step up from the SP (Super polaris) mount. It was Vixen's best mount in the mid capacity class.

#16 Jeff B

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Posted 10 July 2009 - 09:50 AM

I would be very curious to know how long it takes the telescopes pictured above to settle down with this test. If that long or longer for visual use it may be just an annoyance, if astrophotography is contemplated it would be a very serious challenge.


Barry:

Beautiful set up there.

To answer your question the damping times from a rap on the eyepiece end are all under 1-2 seconds with the 5" F8 with the GM8 and SP being the fastest and slowest respectively to settle out. The 5" F8/GM8 combo would settle out in 1 second or less...a very effective system.

The 6" AP & Jaegers would settle out in about in about 1.5 seconds with the AP being the quickest.

My criteria for visual use is the ability to focus easily at high powers (in excess of 40X per inch of aperture) without annoying high frequency vibrations. Low frequency oscillations are ok if the amplitudes are small.

To do this I pay attention to tube balancing in RA & DEC (a smidge out of balance actually)and the tension applied to the clutches on each axis. The clutches in particular (both the GM8 and SP/GP) can have a significant influence on the degree and acceptability of the vibration signature. For visual use, I tighten them enough to allow the drives to perform properly but can still be easily moved by hand with moderate resistance. I've found that socking down the clutches can stiffen the structure up too much and introduces the annoying higher frequency "ringing". This is contrary to what I have to do for GOTO operation and I would imagine imaging where you want to keep the vibration amplitudes as small as possible.

The ground surface also has a very significant influence on vibration with the softer surfaces working much better. I always use damping pads on hard surfaces.

If I can get acceptable results for visual use with a humble SP and stock tripod using an older AP 5" F8 then a GP-DX with a better tripod is sauce for the goose.

Of course, there is subjectivity involved concerning what's acceptable in terms of vibration for visual use.

Jeff

#17 GShaffer

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Posted 10 July 2009 - 02:12 PM

I have one of each....SP-DX and GP-DX.....other than the electrics there doesnt appear to be a lot of difference....ie the motors use different connectors, things like that.

The SP-DX is a bit heftier than the GP-DX and if you can find one used is a viable option. Nice mount. regards Greg N



#18 BarrySimon615

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Posted 10 July 2009 - 05:03 PM

I have one of each....SP-DX and GP-DX.....other than the electrics there doesnt appear to be a lot of difference....ie the motors use different connectors, things like that.


I would agree with this, the major differences between the two being the look, and what I think to be more functional setting circles on the older SP-DX (larger). The key difference being the fact that the newer GP-DX as well as the GP utilize a dovetail mounting system where the older SP-DX and SP require hard mounting of the telescope rings to the top of the declination assembly.

Barry Simon

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#19 Renae Gage

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Posted 10 July 2009 - 11:19 PM

The GM8 did a very good job of even supporting my AP 152 F9.

Jeff


Ouch! Get thee a G11... :roflmao:

#20 GShaffer

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Posted 11 July 2009 - 12:37 AM

I think perhaps JeffB's definition of a "good job" and yours and mine might be just a tad skewed :)

The GM8 did a very good job of even supporting my AP 152 F9.

Jeff


Ouch! Get thee a G11... :roflmao:



#21 Jeff B

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Posted 11 July 2009 - 11:11 AM

The GM8 did a very good job of even supporting my AP 152 F9.

Jeff


Ouch! Get thee a G11... :roflmao:


You mean like this? :grin:

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