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Old 21-05-2008, 10:02 AM
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How accurate is your autoguiding?

Hi All
I'd be interested in knowing how accurately people manage to autoguide and with what equipment. What is a realistic target in terms of pixels on the AG camera?
Geoff

Last edited by Geoff45; 21-05-2008 at 02:51 PM.
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Old 21-05-2008, 10:33 AM
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Geoff, not sure about pixels and that sort of stuff, but I giude with a Philips Toucam through a WO 80mm FD scope, which is all hooked up to the G11, never had any problems to date and it dose a really good job.

However there are times when it is a bit hard to find a guide star in certain areas of the sky, but on the whole it is pretty accurate.

Having said that I have now invested in a Orion Star Shoot for the G11, which will be able to pick up more stars, as it is a bit more sensitive than the Web Cam.

Leon
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Old 21-05-2008, 10:41 AM
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Originally Posted by leon View Post
Geoff, not sure about pixels and that sort of stuff, but I giude with a Philips Toucam through a WO 80mm FD scope, which is all hooked up to the G11, never had any problems to date and it dose a really good job.

However there are times when it is a bit hard to find a guide star in certain areas of the sky, but on the whole it is pretty accurate.

Having said that I have now invested in a Orion Star Shoot for the G11, which will be able to pick up more stars, as it is a bit more sensitive than the Web Cam.

Leon
Yeah Leon, you'll be pleased with the Orion Star Shoot. With my 70mm guidescope, I have never yet had a case where there wasn't a guidestar in the field of view.
Geoff
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Old 21-05-2008, 10:54 AM
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I guide with the QHY5 a W066 and image with the Canon20d on the VC200L, normally at f6.3. The setup rides on a Sphinx SXW. I guide with Guidemaster v 2.0.25 using the outputs on the QHY5 to drive the ST4 inputs on the Starbook. Typically guide accurcy over 3-5 mins is +/- 2" as reported in the GM logs.
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Old 21-05-2008, 11:35 AM
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ST4 vs Ascom autoguiding

Hi Guys, on this topic, I am planning to drive an LXD75 via ASCOM driving from the PC via serial cable to the Autostar hand controller... I'm assuming as this is less "direct" it wont be as accurate as ST4 port driven autoguiding?
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Old 21-05-2008, 11:46 AM
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Originally Posted by Robert_T View Post
Hi Guys, on this topic, I am planning to drive an LXD75 via ASCOM driving from the PC via serial cable to the Autostar hand controller... I'm assuming as this is less "direct" it wont be as accurate as ST4 port driven autoguiding?
but what camera and program on the PC will you be autoguiding with? ASCOM is only to sync the PC with the handcontroller to where it is pointing and controlling the slewing of the scope? So no you wont be autoguiding
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Old 21-05-2008, 12:03 PM
ozstockman (Mike)
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Hi Geoff,

I guide with ED80(f/7.5) and take pictures with 8" SCT(f/10) reduced to f/6.3. My mount is EQ6 Pro, guiding camera is qhy5 camera and I am using PHD with "on camera" option.

Guiding seems to be quite accurate for me even though the focal length of my guiding scope is twice less than the focal length of my imaging scope.

I was also trying pulse guiding twice with the same setup and EQMOD connection to the mount but I was unsuccessful. It did not seem to guide as good as when it's using a ST-4 port on QHY5 I'm sure pulse guiding can be used on EQ6 pro via EQMOD and ASCOM as there are a lot of guys on EQMOD yahoo group who say that it works fine. However I just guessed then that there was something wrong with my settings related to guiding in PHD/EQMOD and decided put it aside for a while and don't wast my time.

The next time I'm going to switch my scopes and use APO as an imaging scope and SCT for guiding. I've got a little more faster APO with f ratio 6.8 and want to see how it goes.

cheers,

Michael
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Old 21-05-2008, 02:08 PM
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Originally Posted by h0ughy View Post
but what camera and program on the PC will you be autoguiding with? ASCOM is only to sync the PC with the handcontroller to where it is pointing and controlling the slewing of the scope? So no you wont be autoguiding
Houghy, I'll be using Phd and either my Phillips webcame or the DMK - does that get me going. Stark labs etc say you can autoguide this way? cheers, Rob
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Old 21-05-2008, 02:35 PM
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You definitely can guide some mounts via ASCOM - I used to operate the SXD way via its ethernet port, it does have greater latency than ST4 though and is generally regarded as less precise as a result.

I am not familiar with the EQ5, can you send corrections to the controller via the serial port.
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Old 21-05-2008, 05:32 PM
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I am not familiar with the EQ5, can you send corrections to the controller via the serial port.
I was planning to do this on my LXD75 which does have a serial port feed on it's autocontroller handset... my eq5 is far more primitive
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Old 22-05-2008, 08:10 AM
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If you have an LXD75 with an autostar controller I think you will not need to use ASCOM, most guide progs will explicitly support the meade LX commmands. You may need a USB to serial adapter if your laptop does not have a serial port - and take care not to have multiple progs trying to use the same COM port (eg The Sky or similar).
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Old 22-05-2008, 11:38 AM
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Guiding error is under +/- 1 arcsec. 5 second guide exposures on a Losmandy Titan with a FSQ-106ED operating at 530mm FL. Hardly a challenge! Quadruple the FL and I'd probably be in for some edge of the seat excitement. Below is a MaximDL screen displaying the details. Such information probably doesn't help the cause, but this is what I routinely achieve. I should note, that the mount has been PEC tuned with PEMPro.
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Last edited by jase; 22-05-2008 at 12:29 PM. Reason: Sorry, I have an ED not N FSQ - fixed typo, not that it matters.
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Old 22-05-2008, 12:29 PM
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Originally Posted by jase View Post
Guiding error is under +/- 1 arcsec. 5 second guide exposures on a Losmandy Titan with a FSQ-106N operating at 530mm FL. Hardly a challenge! Quadruple the FL and I'd probably be in for some edge of the seat excitement. Below is a MaximDL screen displaying the details. Such information probably doesn't help the cause, but this is what I routinely achieve. I should note, that the mount has been PEC tuned with PEMPro.
This is the sort of result that you'd expect, but my GM8 has about 3 times this sort of error. Is the PEMPro worth the money?. Also, is there any sort of problem with the autoguider and the PEC correction fighting with each other?
Geoff
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Old 22-05-2008, 01:22 PM
jase (Jason)
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Originally Posted by ghsmith45 View Post
This is the sort of result that you'd expect, but my GM8 has about 3 times this sort of error. Is the PEMPro worth the money?. Also, is there any sort of problem with the autoguider and the PEC correction fighting with each other?
Geoff
Hi Geoff,
Before you start autoguiding, try to eliminating as many possible sources of bad tracking. Balance, polar alignment, Periodic Error (PE).

Balance is a relatively easy one to gauge and resolve. Polar alignment is a critical one, which of course can be mitigated through good drift alignment techniques. If you find that your autoguided images have a central star that all other stars rotate around, you polar alignment is off - that is an extreme case however.

Try to reduce your raw PE through a combination of mechanical tuning and software (if possible). For instance, after many tests I found my DEC worm provided a slightly less rate of error than the RA, so I swapped them. The RA error was my main concern as with excellent polar alignment, your RA is the only axis that will move. After doing so, I noticed a reasonable improvement to tracking. Now I know not all mounts will allow you to do this, but if you can, its worth investigating to determine if there a plausible gains. Tweak backlash between by optimising the space between the teeth and worm if possible. Are you experience erratic vibrations (perhap high frequency)?

If your mount supports PEC, program it. Any form of PEC is usually better than none. Again, keep in mind what you are trying to do is improve your tracking accuracy. Record PEC on a single guiding run or use software such as PEMPro to average multiple worm runs (averages seeing and random errors). PEMPro is a great piece of software in my opinion, but others have had mixed results. Part of the reason could be experience. You may need to inverse the PEC curve PEMPro creates before programming your mount and there are a few other "gotchas".

Once you feel you've nailed all of the above to the best of your ability and equipment capability, commence autoguiding. Autoguiding has the ability to mask many of the above errors, hence the reason for this pragmatic approach. If you find your autoguider corrections are working over time, stop and think about why this is occuring. The less autoguiding corrections made, the better your images will be. I look at autoguiding as a fail safe or "patch" to hide all your mounts limitations. It can only do so much, hence prevention is better than a cure. As everyone says, sink all your money into a quality mount, optics and cameras can come later.
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Old 22-05-2008, 03:04 PM
Ian Robinson
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Just my 5c worth.

So long as your guiding errors are less than one pixcel , then your guiding is good enough I would think.

Good physical polar alignment is the key.
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Old 22-05-2008, 04:06 PM
jase (Jason)
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How big is a pixel? 7.4u, 9u, 12u squared. How many arcseconds does that pixel cover based on your optical configuration? What if you 2x2 bin your guider to boost sensitivity (i.e. turning a 9u into a 18u)? How does the guider pixel size differ from your imaging chip pixel size?

You'll find mount manufacturers judge their performance on peak-to-peak arcseconds. Arcseconds are a definitive measurement, pixel values are too variable and to be honest could mean absolutely anything depending on what your arcsec/pixel optical configuration is.

Keep in mind that guiding algorithms determine a star's centroid with sub pixel precision.

If you are looking for a bible on auto guiding, look no further than the attachment below. Jim McMillan is renown for his guiding techniques and code he has written including the MaximDL plugin Multi-Star guide where you can guide on multiple guide stars to minimise chasing the seeing.
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File Type: pdf AutoguidingMcMillian11-2005.pdf (138.6 KB, 330 views)
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Old 22-05-2008, 05:16 PM
Ian Robinson
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All that is true , you can easily calculate the size (in arc-seconds) of a pixcel on your guide camera , and more importantly , on the imaging camera given the focal length of the scope or lens..

It is pointless aiming at better than the pixcel resolution of the imaging camera as there is nothing to be gained for a lot of extra work (and expense).
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