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Vixen Sphinx SXW GoTo accuracy?

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#1 Taylor

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Posted 13 July 2009 - 01:44 AM

Just toyed around with my new Vixen Sphinx SXW mount a few days ago when we had a couple nice nights here in Seattle.
To anyone out there with a Sphinx as well, how are your GoTo's?
I've been spoiled by a Nexstar GPS mount which was one of the most accurate 2-star alignment telescopes (in alt-az mind you) I've ever seen.

Trying to setup my Sphinx in EQ mode with aligning to two stars has yielded less than desirable results.
Reading around online about the Sphinx from other users, it seems like I need to align to two different stars that are 10 degrees apart on both sides of the meridian.

Does anyone else's use reflect this? If this is the case I'm fine with it as aligning to 4 stars takes little time and the Sphinx is such an awesome machine it would be worth it.

#2 adamsp123

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Posted 13 July 2009 - 06:37 AM

I have a Sphinx and Atlux, and if polar aligned the gotos are excellent. If only roughly aligned then using the alignment feature i found gotos in the same area of the sky are good. What they don't like is setting up a series of alignments all over the sky, this leads to bigger errors so I do alignments based on where I want to observe or image and if I go for a big change of coords I do a realingment based on stars/objects in the new area even picking the same stars to use more than once but this process is quite quick using the starbook.
BTW do you use a illuminated graticle EP for your alignments this helps as well to get the object centered accurately.

#3 Renae Gage

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Posted 13 July 2009 - 09:59 AM

I agree on the accuracy of the NS-GPS. It's ruined me with unmet expectations for every goto since.

With a GEM, if polar alignment is off, the gotos will be as well. I never thought of precise polar alignment as an optional activity. That's part of the attraction of alt-az.

#4 rmollise

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Posted 13 July 2009 - 10:04 AM

I agree on the accuracy of the NS-GPS. It's ruined me with unmet expectations for every goto since.

With a GEM, if polar alignment is off, the gotos will be as well. I never thought of precise polar alignment as an optional activity. That's part of the attraction of alt-az.


Not on all GEMs. Celestrons, for example, don't require anything like accurate polar alignment for go-to accuracy. Example? One of our club members, new to the game, hauled his wonderful new C8-SGT out to the dark site. He pretty much got it up and aligned by himself. An hour or so later, though, he trotted over to my observin' position:

"Uncle Rod, all the objects I ask for are in the eyepiece, but they don't STAY THERE."

A quick look revealed that he'd "polar aligned" on Kochab not Polaris.
:lol:

His go-to accuracy was quite respectable, howsomeever...

#5 Renae Gage

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Posted 13 July 2009 - 12:12 PM

Celestron's GOTO's are without peer, at least in my price range.

#6 sctchun

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Posted 13 July 2009 - 02:30 PM

Hi Taylor,

I align my sphinx using 2 stars on each side of the meridian (4 stars total). As well as aligning the mount using the Polar alignment scope.

Steven

#7 Luigi

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Posted 14 July 2009 - 06:59 AM

>>>Uncle Rod, all the objects I ask for are in the eyepiece, but they don't STAY THERE.<<<

You wonder why they don't simply drive the Dec axis to correct for polar misalignment. They drive both axes when tracking with their alt-az mounts so it's not that tough to do and would be a boon for the equatorially challenged.

#8 jrcrilly

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Posted 14 July 2009 - 08:07 AM

You wonder why they don't simply drive the Dec axis to correct for polar misalignment.


Vixen did offer that option in their previous GEM controller (SS2K). I am told that the Sphinx has it also, but if so I failed to find it in the ones I owned.

#9 amys

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Posted 14 July 2009 - 10:21 AM

For best results, I use at least 2 stars on to the west and then 2 stars to the east. Don't go back and forth across the meridian for the alignment. And then I align as I observe. It only takes a few seconds and the Sphinx allows up to 20 alignment objects. I always use a reticle eyepiece as well.

I've been using a CG-5 for the last few months and have been very impressed with the accuracy of the go-tos using the 2-star alignment with 2 calibration stars. I just find the alignment process on the Sphinx easier.

#10 Taylor

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Posted 14 July 2009 - 11:07 AM

Well the problem is when observing from home its in a suburb of Seattle, so the whole point of aligning for me is to accurately GoTo fainter objects without having to align on them each time.
So I would prefer a one-time alignment procedure at the beginning of the observing session and to expect GoTos to be within the field of my 21 or 17 Hyperion.


#11 amys

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Posted 15 July 2009 - 11:22 AM

That works too. I just like to observe stuff as soon as I start out, so I align as I go along.

#12 scope dog

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Posted 15 July 2009 - 04:44 PM

I really feel this "if align+level is a backlash issue. Having a SSK2+CI700H and Atlux Skybook. Due to weather and work I have not had a chance to play with this. With meade lx200 and nexstar they recommend setting backlash. I know with meade it was land mode setting backlash is done on each axes.
Though with the Atlux there is little play with the worms and I am sure with the SXW. The primary play is the gears in the motors. The skybook has back-lash settings and there is a proceedure to do so. As you perform multi alignment if the backlash is off by .05 this will add up like 5 or more and confuse the alignment process. Regarding the Atlux manual the proceedure is on P42, however with any goto system it should be on page one.

#13 Taylor

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Posted 15 July 2009 - 07:36 PM

Thanks scope dog, I'll give that shot next time I have some time to work on it.
Right now I'm putting in a lot of hours rebuilding my great-granddady's 90 year old Winchester shotgun and studying for the GRE, so I'm not out enjoying the clear skies as much as I should be.

I really wish there was someone in one of the Puget Sound's astro clubs with a Sphinx, the Starbook hand controller is not like any of the others that I've ever used.

#14 rmollise

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Posted 16 July 2009 - 06:59 AM

>>>Uncle Rod, all the objects I ask for are in the eyepiece, but they don't STAY THERE.<<<

You wonder why they don't simply drive the Dec axis to correct for polar misalignment. They drive both axes when tracking with their alt-az mounts so it's not that tough to do and would be a boon for the equatorially challenged.


Seems like this would be easy enough to do. Course, you'd want to be able to turn it off, too.

All in all, jus' mashin a N/S button is prob'ly the easiest way.
;)

#15 Taylor

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Posted 17 July 2009 - 01:06 PM

Had the Sphinx out again last night, it was a great night! (until Seattle's clouds graced me with their presence...)
While setting it up last night I spent a little more time trying to get a little more precise with its polar scope, although I still feel like I wasn't spot on with it. I think that got me off on the right foot right there.
Next, I followed the advice of members of the Sphinx Yahoo group, and aligned to two stars on the east side of the meridian, Alkaid and Arcturus if memory serves, and two stars on the west side of the meridian, Vega and I believe Altair. I still wish I had an illuminated reticle eyepiece for spot-on alignments, but my 8mm Hyperion and some estimation did the trick for last night.
After that, my next several GoTos were all within the field of my 8mm Hyperion. This result is quite the opposite the complaining of the Sphinx that I have seen online, seems like its getting a bad rep for nothing!
I then slewed the scope back to the east, aligned it on Arcturus for good measure, and slewed it to M3. The mount put it within my 8mm Hyperion, although near the edge. I centered the cluster and then attached my Canon 10D.
Attached is an image I took that was 30 seconds at ISO 1600. Looking back I wish I would have turned down the ISO and took longer a couple longer exposures just to see how long the Sphinx could track at f/7.5 unguided. I'll do that next time I'm out.
As a side note that is my first ever DSO image, now that I can actually center and focus it, I guess the next step in progression is optimizing my subs to my locale (read, light pollution!) and processing. I think there is also dust on the 10D's sensor.

Anyways, thats my quick review of the Sphinx and to show it doesn't deserve the bad rep its seen online.
I like it so much I'm considering writing a review on it for CN's EQ mount review section when I have the time later this summer.

Posted Image

#16 amys

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Posted 17 July 2009 - 02:32 PM

I'm really glad you're happy with your SXW. Most of the negative reports I have seen about Vixen Sphinx mounts actually involve the SXD, not the SXW. I find the Sphinx very easy to set up, especially compared to the CG-5 I have. I much prefer the simple design of the Sphinx, which requires far less counterweights than the CG-5, and I do like the Starbook, since I'm always looking at a star chart when I'm using it. Since I don't do AP, I don't even bother using the PAS anymore. I just level the tripod, place a compass set to my declination on the top plate, and adjust tripod so the notch is pointing to true north. This gets me observing well before dark I find the go-tos and tracking are quite good.

Enjoy!

#17 adamsp123

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Posted 17 July 2009 - 03:26 PM

Glad you got a good night with the Sphinx, there is no doubt in my mind that set up correctly the goto works fine and the use of local stars for alignment to get good gotos works well.
In the Vixen Atlux manual using the same starbook computer it recommends that for best goto accuracy only use nearby stars to the object for alignment it states that using stars far apart across the sky will lower the starbook goto accuracy.

Nice pic for 30 secs now you will join the AP dark side!
As for photos try stacking many pics in RAW mode using Deep Sky stacker, for example try 20x30secs plus 20x1min at ISO 800 letting the camera cool for 15-30 secs between pics.
Then process using the free paintshop pro program link below

http://www.atomicmpc...Download/150212,corel-paint-shop-pro-x.aspx
you need the full URL
You might need a light pollution filter as well.
Pete

#18 sctchun

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Posted 17 July 2009 - 03:29 PM

Hi Taylor,

Congratulation on your first shot. It looks good, I'm not sure what you are using for camera control and processing, but I would like to suggest you look at Images Plus (www.mlunsold.com).

Also I have some other suggestions that may help.

1) If you haven't gotten one, a bathinov mask helps alot in getting focus.
2) Get a Red Dot finder to help you align your scope.
3) Get a 90 degree periscope for your camera (There are some generic ones availble). Then perform your alignment with the camera in place instead of the eyepiece, it will help in getting your frames centered.
4) Check the Yahoo group, there is a procedure to align the PAS.

BTW, I'm able to get 2 min unguided with my 80mm F6 scope, I probabily could get longer, but I haven't tried.

Steven






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