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Old 28-09-2007, 10:57 AM
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dugnsuz (Doug)
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Off Axis Guider + Webcam for Autoguiding

Hi All,
Does anybody have any experiences of using an Off Axis Guider + Webcam for autoguiding.
Came across this link (obviously it can be done)...
http://www.asnsw.com/photos/dme.asp
Sounds a cheaper alternative to guide scope, rings etc
I would be using the ED80 as both imaging and guidescope!!!
Any thoughts?
Doug
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  #2  
Old 29-09-2007, 08:51 PM
Alchemy (Clive)
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put in reply on your next post. i did a search on google aus for off axis guider and came up with all the previous ice in space posts which have lots of info( being as everyones ignored you so far), they are there i dont knowhow the IIS search engine works, maybee you do.... as this issue has been enquired about before.
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  #3  
Old 29-09-2007, 09:35 PM
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I've heard that you can effectively autoguide with an Off Axis Guider, I haven't had any success personally (in fact I hate the dam things).
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  #4  
Old 29-09-2007, 10:32 PM
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well I have one and I have found it to be as Paul describes. I now prefer the piggybacked 80ED to guide through
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  #5  
Old 29-09-2007, 10:39 PM
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Quote:
Originally Posted by h0ughy View Post
well I have one and I have found it to be as Paul describes. I now prefer the piggybacked 80ED to guide through
What's the problem - locating guide stars, focussing...all of the above!!?
Cheers for any help
Doug
PS... I had thought about getting a Lumicon 2" easy guider as i thought that this would be of a better quality than the Meade, Celestron models,...
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Old 29-09-2007, 10:47 PM
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Quote:
Originally Posted by dugnsuz View Post
What's the problem - locating guide stars, focussing...all of the above!!?
Cheers for any help
Doug
PS... I had thought about getting a Lumicon 2" easy guider as i thought that this would be of a better quality than the Meade, Celestron models,...
yes your right - its pretty heavy. I have the giant easy guider (got it from Strongman Mike) he used it sucessfully with his Meade 12", but I find it too hard to get a guidestar.
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Old 29-09-2007, 11:30 PM
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Quote:
Originally Posted by h0ughy View Post
yes your right - its pretty heavy. I have the giant easy guider (got it from Strongman Mike) he used it sucessfully with his Meade 12", but I find it too hard to get a guidestar.
The SCT guider is a monster! The one i'm looking at is a much smaller model...
http://www.lumicon.com/telescope-acc...Guider+2in&hn=
It would screw on to ED80 focuser with hopefully minimal trauma!!!
Cheers
Doug
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Old 30-09-2007, 07:13 AM
Alchemy (Clive)
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you will find that because the off axis guider is picking off stars at the edge of field , all your abberations come into play.... unless you have a flat field scope......... which the ed80 is not.

the previous general historical concensus was to go with a separate guidescope really solidly attatched

piggybacking is a good place to start and you can just guide straight through the scope and get used to the guiding, also with the reduced focal length you will get pleasing results straight away.
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Old 30-09-2007, 09:46 AM
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Quote:
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you will find that because the off axis guider is picking off stars at the edge of field , all your abberations come into play.... unless you have a flat field scope......... which the ed80 is not.
Thanks Al,
Hadn't considered this - do the stars have to be perfect points for the guiding software to lock on?
Cheers
Doug
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  #10  
Old 30-09-2007, 10:17 AM
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Guiding on a distorted star isn't such a problem in its self - no guiding software I have tried has ever had a problem locking on to and guiding on a illongated star for example. But the problem is how that image of that star behaves with respect to a normal/correct star in the centre of the field. The way I visualise it is if you imagine looking through a ball of glass that causes distortion, you pan across a field of view, objects at the edge move slower than at the centre, or in different paths. Whie that's obviously an exaduration I imagine the same sort of thing would happen when you're looking at a guide star on the edge of your FOV vs a star in the centre of your FOV, assuming your FOV is not perfectly flat and uniform. Of course in theory your stars are staying steady in the FOV so there's no movement to result in a different rate of movement in the guide star vs centre star, but I'd expect it to affect accuracy.

Disclaimer: This is just stuff I've thought about and figured would be hapenning when I've considered the same sort of thing on my scope, I don't know for sure if I'm right on any of the above.



Roger.
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Old 30-09-2007, 10:21 AM
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The other thing to consider is that your autoguiding software is trying to guide on the center if the stars image, if the star moves closer to the edge of your lens then the distortion is going to increase, this may well have the potential to change the location of the stars center as the part of the image nearest the edge will distort first and furtherest.

If you can follow that reasoning
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Old 30-09-2007, 10:28 AM
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Thanks Roger for your explanation - makes sense.
I think I may have to bite the bullet and hang out for a decent guide/imaging scope to complement the ed80. Perhaps a 66mm WO apo?
Load-wise it wouldn't traumatise the mount and would be an excellent wide field imaging scope too - I'll have to save a bit more, but the time will give me an opportunity to get used to the autoguiding setup and process with the ED80.
Thanks again.
Doug

...it's only money eh!?
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  #13  
Old 30-09-2007, 11:41 AM
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Hmm, well that lumicon off-axis guider you posted the link to us US$199 ... Say you could get that for AU$260ish then.....

Skywatcher 70x700 OTA: AU$150
100mm Scope ring set from ADM: US$69+S/H
Total: About AU$250

Might be extra if you need some sort of attachment to put the rings on your setup.

Anyway, point is, you might be able to get a guidescope for the same or very near the same price.



I use the 70x700 for guiding. Weighs so little you'd think it's a finderscope, but surprisingly sharp optics with focus lock and good focus travel. Very suitable and cheap guide scope. I use those rings too.

Roger.

Edit: ADM: http://www.astro.premcom.com/ADM/
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  #14  
Old 30-09-2007, 12:10 PM
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Hi Roger,
After reading yours and other's thoughts on off axis autoguiding, I've reconsidered as stated in the post above.
I was looking at a lumicon guider from a seller on astromart at $130US so it would still have been about $180AU after postage from US was added.

I'm considering a pair of 100mm WO guide rings for sale here on the forum if they fit my setup without having to break the bank by buying heaps more mounting accessories!! Probably work out about the same price as the ones in the link you provided.
That leaves about $300 in the budget for guidescope, Telescopes and Astronomy in Adelaide have a WO 66mm Apo for $473 which looks very nice or the 66mm Petzval for $330. I really fancy the little APO - probably end up imaging more with that than the ED80 though
Just have to save the pennies a wee bit longer!
Cheers
Doug
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  #15  
Old 30-09-2007, 12:10 PM
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Hi Doug

This is my field setup with aSW ED80 Pro and WO 66SD guidescope, ADM guide rings riding on a GM-8.

Cheers
Attached Thumbnails
Click for full-size image (IMG_0514 (Large).JPG)
99.6 KB71 views
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  #16  
Old 30-09-2007, 12:17 PM
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Quote:
Originally Posted by dugnsuz View Post
...WO 66mm Apo for $473 which looks very nice or the 66mm Petzval for $330. ...
I didn't realise the WO 66mm was only $473, that's a nice price I know what you mean about it being nice to have a little APO like that, it'd be a neat addition to any setup
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Old 30-09-2007, 12:20 PM
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Hi Doug

This is my field setup with aSW ED80 Pro and WO 66SD guidescope, ADM guide rings riding on a GM-8.

Cheers
Drool...
Looks solid as a rock John!
That's pretty much the setup I'll be using (minus the GM8!)
Cheers
Doug
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  #18  
Old 30-09-2007, 12:22 PM
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I didn't realise the WO 66mm was only $473, that's a nice price I know what you mean about it being nice to have a little APO like that, it'd be a neat addition to any setup
Here's the link to the price list, don't know if there's any in stock though!

http://www.telescopes-astronomy.com....tar_megrez.htm

Cheers
Doug
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  #19  
Old 30-09-2007, 12:24 PM
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John,
What is the focuser assembly on your ED80?
Doug
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  #20  
Old 30-09-2007, 12:25 PM
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Quote:
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Drool...
Looks solid as a rock John!
That's pretty much the setup I'll be using (minus the GM8!)
Cheers
Doug
It is rock solid, I am using a G-11 Tripod.

Here is a link to a picture taken with this setup, guided using an LPI through the WO 66SD.

http://www.pbase.com/takman2/image/85557243

Cheers
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