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Equipment Discussions >> Mounts

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Startraffic
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5634759 - 01/21/13 11:30 AM

Contraf15,
What is the time period of the RA jump? That should give you a clue as to where it's coming from.

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contraf15
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Re: Is this performance typical of G11? new [Re: Startraffic]
      #5635934 - 01/21/13 11:15 PM Attachment (80 downloads)

That's one of the problems...it isn't periodic. I'm attaching a 15-minute log file from this evening. I was guiding with an ST-i, SBIG OAG through a Stellarvue SV80ST with a TeleVue 0.8x reducer. With the reducer the scope has a 384mm focal length, so the pixel scale for the STF-8300 is 2.9 arcsec/pixel. Even at that scale the RA deviations are obvious in the main camera images. The SBIG OAG provides a further reduction of 0.7x, so the guiding focal length is approximately 269mm. That gives a guiding pixel scale of ~5.7 arcsec/pixel. You can see in the log file sudden deviations of up to 4.2 pixels (I've seen as high as 9 on occasion). That's from 24 to 50 arcsec of sudden movement! Of course this makes exposures of any length worthless because it happens so frequently and is totally unpredictable. I must be missing something...any ideas??

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Hilmi
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5636064 - 01/22/13 12:59 AM

I'm seeing similar issues, the guide plot looks so erratic! Bounces all over the place. Tried fiddling with guiding aggressiveness etc... no effect. Guide through pulse guide and through ST4 connection, no joy. Try using PEMPro, and PE is so low and the curve is very smooth. Can't recall the figures I am abroad now and I am far from my imaging laptop, but PEMPro is showing me a smooth curve and PE in line with the results reported for Ovision worms.

Can you try the same thing on your side Contraf15? Measure PE without guiding.


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orlyandico
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Re: Is this performance typical of G11? new [Re: Hilmi]
      #5636081 - 01/22/13 01:13 AM

if there are sudden jumps that seems like slack in the RA gearing... or on the other hand maybe the worm is too tight and the jumping is due to stiction..

maybe try loosening the RA worm engagement. i have no G11 but on my CGEM, when the RA slack is very small (tight worm-to-gear mesh) there are a lot of problems. These go away when the worm is looser.


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contraf15
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Re: Is this performance typical of G11? new [Re: orlyandico]
      #5636271 - 01/22/13 06:14 AM

I suspected the gear mesh might be the culprit, so last night I adjusted it across the full range allowed by the thumb screw on the one piece worm block. There was no change.

Hilmi I will try to get a PE measurement within the next couple of days.

Jeremy


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orlyandico
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5636291 - 01/22/13 06:32 AM

this is not an option for Hilmi, but i bet if you send it to Ed Thomas at deepspaceproducts he would be able to resolve this.

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contraf15
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Re: Is this performance typical of G11? [Re: orlyandico]
      #5636295 - 01/22/13 06:37 AM

I'm sure he could, but for the ~$4000 I have invested in this brand new mount I shouldn't have to send it to someone to get it tracking correctly

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orlyandico
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5636346 - 01/22/13 07:42 AM

Good point. But I do know folks with G11s and they don't have these problems.. I bet its something really simple.

Have you tried calling Losmandy? (as opposed to emailing or going to their forum)


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Startraffic
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5636614 - 01/22/13 10:40 AM

Contra15,
I pulled your tracking into a spreadsheet & looked at it. I found some inconsistencies, The number of intervals per hour is erratic anywhere from 12 to 17 intervals per hour and the time between those intervals is anywhere between 3" to 7". So the tracking itself isn't consistent nor is there a pattern that I can see (i.e. the dreaded 44" error), There also seems to be a connection between the brightness of the guidestar and the time between the tracking intervals. It seems that if there is a change in brightness up or down of greater than 2000 the time between the corrections is longer. This would cause the amount of correction to be greater.
Is your guidestar bright enough?
Are you having trouble "seeing" the star with the guidescope?
It seems like the guidescope may be chasing seeing. I could be wrong but it feels that way. It might be worth trying unguided vs guided to see if the problem still can be isolated that way.


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contraf15
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Re: Is this performance typical of G11? new [Re: orlyandico]
      #5636720 - 01/22/13 11:46 AM

I think it must be something simple as well. It is a big enough deviation that I must be missing something. I hope so, anyway.

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contraf15
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Re: Is this performance typical of G11? new [Re: Startraffic]
      #5636747 - 01/22/13 12:01 PM

Startraffic,

Thanks for taking a look at the data. Maxim was set up for 3 second guide exposures when I took this data. It looks like it actually updated somewhere between 3-4 seconds depending on the cycle.

I noticed the same thing you pointed out with the brightness fluctuations. The star looked as good as I have been able to get with the OAG at this f-ratio (4.8) and the seeing was pretty good. The guide stars are definitely not pinpoints, but they are fairly bright and seem consistent. This data is typical of what I have seen on other nights with other guide stars.

I think my next course of action will be as follows:
1) Test the PE with no guiding as Hilmi suggested
2) Try unguided exposures and see if the stars look any better
3) Try guiding through a separate scope (maybe the field curvature is playing havoc with the OAG?)
4) Try the OAG with another, slower scope with a flatter field (I have a 127mm f7.5 that has a very flat field, haven't tried it yet with the new equipment).

I'll post my results.

Jeremy


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JoseBorrero
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5637256 - 01/22/13 04:17 PM

well, I have some mixed experience in the past with my G11, I replaced the worm to the losmandy one with same worm, but at same time, I bought the miniguider scope from zhumell same as Orion brand together with the Starshoot autoguider and I always use PHD, unluckly maxim doesnt work much for me on guiding. Now I'm getting the lowest RMS ever on PHD, I did test it with my AT6RC at f/9 and got best rounds stars ever. Which so small and widefield miniguide scope guiding on bright stars almost always my PHD exposure time is best a t 0.2 sec that is pretty much live. I can't really tell if the block was the problem or the miniguide scope focal lenght helped.

My second setup that work pretty similar was using an Orion ST80 with SSAG in Tandem with an Orion ED80. I have so many mixed results. Some night I took long times just recording PHD settings. From 3 setup optics I have two different PHD settings written in a book so I can forget and use over and over, those that have produce very good results.

It is very possible that just trying PHD and trying different settings may help. also a miniguide isnt expensive at all to try. I got the TS9 OAG and now is just set there with no job as the miniguider is the winner.


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NJScope
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Re: Is this performance typical of G11? new [Re: Hilmi]
      #5637953 - 01/22/13 11:00 PM

Hilmi

If you physically disconnect the guide scope cable from the Losmandy mount do you still see the erratic jumps in RA? About a year ago I purchased an SBIG ST8X camera with auto guide to replace an ST402ME and external guider. I immediately had problems with erratic guiding in RA which after months of investigation was solved by the purchase of SBIGs optocoupler. According to the manual my particular Losmandy G11 should not have required one, however, it clearly fixed the problem.


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Hilmi
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Re: Is this performance typical of G11? new [Re: NJScope]
      #5638057 - 01/22/13 11:54 PM

Thanks for the suggestion Kevin, but I have tried guiding through ASCOM driver without the ST4 cable with the same results. So I don't think that's it.

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Re: Is this performance typical of G11? new [Re: Hilmi]
      #5638160 - 01/23/13 01:25 AM

wow.. 12 to 17 sounds like its sticking.. especially when you say it jumps...

if it is sticking, you can watch an inline amp meter to watch the amps jump up when it hits that point.. Motor will get hot too..

A TDM would solve your issue. i'd still worry about the motors getting too hot..


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Hilmi
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Re: Is this performance typical of G11? new [Re: wolfman_4_ever]
      #5638170 - 01/23/13 01:33 AM

And here comes the TDM marketing plug :P

Just pulling your leg


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orlyandico
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Re: Is this performance typical of G11? new [Re: Hilmi]
      #5638174 - 01/23/13 01:41 AM

G11 G2 + TDM is very close to the price of a Mach1... and to those who say a TDM will outperform a Mach1, well maybe it will and maybe it won't. But mine does 0.42" peak to peak after PEM. A PE that low is in the same range as a TDM.

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contraf15
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Re: Is this performance typical of G11? new [Re: wolfman_4_ever]
      #5638313 - 01/23/13 06:57 AM Attachment (32 downloads)

The motors do not get hot. At all. And while I appreciate that Ed Thomas or the TDM or a variety of other things would solve the problem (including a Mach 1), so would buying the McDonald Obsevatory. This is a brand-new mount that is capable of much better guided performance than it is giving, and I'd like to figure out what is getting in the way.

Given that my guiding logs show a dramatic change in guide star intensity every time one of these deviations occur, I decided to take the STi out of the OAG and mount it in a 50mm guidescope to see if that would make a difference. I'm still not sure if the change in brightness is a cause or an effect of the RA guiding deviations. Well, just my luck the tube was too short to bring the STi to focus. So I replaced it in the OAG but cut an aluminum shim to keep it orthogonal in its socket (who at SBIG came up with the design of that thing? There is a huge gap in the socket and just two nylon thumbscrews to hold the camera! You can tighten it down through a wide range of lens-to-chip of angles). I digress...

With the camera better positioned in the OAG, I was actually able to get round guide stars for the first time. I let the mount guide all night long while the imaging camera took 300 second exposures. Lo and behold, the frequency and severity of RA deviations decreased (but they did not go away). The screen shot attached tells the story...fairly stable guiding graph in DEC and RA, with occasional RA deviations of up to 2.5 pixels (~14 arcsec). You can see from the background image what this is still doing to the stars.

So what does all this mean? The deviations still happen, so I'm not sure (and the log still shows a decrease in guide star brightness at those times). I don't think this is about chasing guide stars. The DEC plot never changes and it is guiding off of the same star. I think movement is occurring in RA, which causes the change in brightness by moving the star in the highly curved guider FOV. But that doesn't explain why repositioning the STi improved the tracking (some of the 300sec subs actually had no deviations, maybe 10% of them).

So I am confused. And frustrated. And tired...


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Startraffic
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Re: Is this performance typical of G11? new [Re: contraf15]
      #5638344 - 01/23/13 07:45 AM

Contra15,
Hmmmm, it looks like there IS a pattern at about 70". I'm now beginning to think grit or possibly a gall on the worm or on of the gears in the gearbox. The worm is an "easy" thing to find, the GB is, of course, a sealed unit. I'd look into swapping the GB & seeing if the problem goes away. (no $$$, just time). If it goes away the I'd contact Losmandy about a warranty replacement GB, (You'll have the proof in your tracking graphs), if not then look to the worm. If the worm is bad then again warranty replacement, if it's dirt that is also easy. I know that's not much help or consolation but there is a solution. We just haven't found it yet, it's also easy for me to say, it's not my mount, but I do understand. BTDT & hated it.
I hate those GB because you can't do any servicing on them. I guess it's time to get back to making mine.

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Raginar
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Re: Is this performance typical of G11? new [Re: Startraffic]
      #5638465 - 01/23/13 09:10 AM

Reminds me of guiding my CGEM in MaximDL. No matter what setting I changed, it wouldn't guide. Swapped over to PHD and immediately had improvement.

I wish Maxim was easier to use


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