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Old 14-11-2011, 03:12 PM
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plugger (Andrew)
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Autoguiding advice

Hello all,

I'm about to take the plunge and buy an autoguider. I'm leaning pretty heavy towards the miniguider path, specifically the Orion Magnificent Mini Autoguider package or a KWIQ Guider package. That said I'm not opposed to buying a Orion Awesome Autoguider package. Any comments?

I plan to utilise the guider on an NEQ6 mount. I'll be swapping scopes between a Celestron C8 and a Megrez 90 dependent on target selection. Initially I'll be using a DSLR or webcam for imaging but I do plan on upgrading to a dedicated CCD in the near future.

Basically I'm curious about any experiences you all have had with this type of setup. Will flexure issues come into play with the standard "finderscope" mount that comes with the miniguider packages? Should I instead look to get a set of rings to hold the unit? Would a side by side mounting plate be a benefit or would it add to flexure issues?

I look forward to your responses. Also, if someone wants to take up the argument as to why I should go down an OAG path instead of have a secondary dedicated guide scope please feel free to share your thoughts.
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Old 14-11-2011, 05:28 PM
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Not sure I can really answer your questions but I have an ED80 and am using a QHY5 through a modified finderscope to guide with - at that focal length is does a grand job.

cheers

niko
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Old 14-11-2011, 05:44 PM
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mill (Martin)
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Andrew the best option is to get the finderscope guider as Niko said.
I have had no problem with flexure and you always fin a guide star.
The oag is very good but you have to set it up in daylight because you have a very narrow point to get the star to focus in the guide camera.
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Old 14-11-2011, 06:52 PM
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mithrandir (Andrew)
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I'd only be a bit concerned that a finderscope guider might be a bit short for the C8. There's a fair difference in guiding 560mm and 2000mm.
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Old 14-11-2011, 07:02 PM
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mill (Martin)
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Andrew the finder guider will guide a 2000mm just right if well polar aligned.
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Old 14-11-2011, 07:26 PM
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mldee (Mike)
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Quote:
Originally Posted by mill View Post
Andrew the finder guider will guide a 2000mm just right if well polar aligned.
I'm more than happy with a finder guider on my RC8 @~1600mm, using pHD and DSI II pro.

When setting PHD, Just try to picture that you need to make big jumps to move a star in the finder guider scope, but you need little finderguider jumps to move the star in the Big scope. Adjust PHD accordingly.

After three years of trying all the guider combinations, to me the lightweight finder guider piggybacked seems to be the most reliable (and simple). See attached pic. I DO use good rings though, so it functions well as a finder too, I don't use a separate finder scope, just a red dot for general use, rarely these days. YMMV but good luck.
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Old 14-11-2011, 07:34 PM
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Merlin66 (Ken)
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Over on the Yahoo Stark labs group, there has been some interesting discussions on guide focal lengths v's imaging focal lengths.
With PHD it comes down to arc sec/ pixel for both systems, and the general suggestion is that the ratio between them should be "optimised" around 5...this means if your guider camera is seeing 2 arc sec per pixel then this would be good to guide your imager at 0.4 arc sec per pixel.
You can use the CCDCalc freeware etc. to get the various numbers.
HTH
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Old 14-11-2011, 07:35 PM
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Me too. I'm guiding right now using a TS 60mm finder and Lodestar. It is on the GSO R/C8" at 1607mm, and guiding like a charm. Firmly attached via some ADM rings and DA's.
I also have the SX OAG in the optical train, but like the finder/guider better.
Gary
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Old 15-11-2011, 12:22 PM
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There was an interesting post by Roland Christen recently on guide scopes.

Basically the guide scope should be mounted on widely spaced rings on the OTA not the OTA's mounting cradle. So that the guide scope floats freely with the OTA.

That makes sense that way if the OTA flexes slightly it will take the guide scope with it rather than differently which causes problems.

So a finder scope mounted to the OTA rather than the OTAs rings or a top dovetail may work a bit better.

Greg.
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Old 15-11-2011, 12:37 PM
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Probably correct, I expect Mr. Christen knows a thing or two about such subjects.

My own view is that I'm not quite ready to start drilling holes in my shiny new CF RC yet, and glue is a very messy one-shot affair

So, the top dovetail which seems pretty rigidly attached to the OTA, is the next best thing, using good ADM attachments and rings, especially when it's just holding a very lightweight finder and camera. Probably more chance of micro-movement in those little rings than in the rigidly-attached ADM D plate on the bottom of the OTA, so the whole OTA+mount should be OK.

If it was a finderguider on a cheap set of rings attached to some cheap OTA rings, then yes, I'd say that would have lots of potential for movement, but the GSO RC8 ringless setup, especially with a lightweight CF OTA, really has a very strong overall structure and the finder guider works well, especially as there's also no internal OTA mirror movement to worry about.

In this scenario, in my opinion the PHD and EQMOD settings are the most critical items in getting round stars. YMMV of course.

Last edited by mldee; 15-11-2011 at 12:39 PM. Reason: grammar
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Old 15-11-2011, 12:43 PM
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Hi Mike,

Yes I am in the same situation with my CDK17 when I use it with a reducer. I don't have enough backfocus for an OAG so I use a top dovetail mounted Vixen 95VMC and an ST402ME.

That works well but I do find the occasional subs that have elongated stars.

Overall I find the OAG solution the most effective though. That is really reliable in giving the roundest stars so far for me.

Greg.
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Old 15-11-2011, 12:55 PM
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mldee (Mike)
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Totally agree, I'm just too big a wuss to want to subject myself to that next level of agony yet......Now if I had a CDK17, there might be bit more incentive
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Old 15-11-2011, 06:59 PM
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Thanks for all the thoughtful responses folks. I appreciate it.

I've ordered an Orion Magnificent Mini Guider package and a set of rings to ensure the setup remains stable.
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Old 15-11-2011, 08:47 PM
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Quote:
Originally Posted by Merlin66 View Post
Over on the Yahoo Stark labs group, there has been some interesting discussions on guide focal lengths v's imaging focal lengths.
With PHD it comes down to arc sec/ pixel for both systems, and the general suggestion is that the ratio between them should be "optimised" around 5...this means if your guider camera is seeing 2 arc sec per pixel then this would be good to guide your imager at 0.4 arc sec per pixel.
You can use the CCDCalc freeware etc. to get the various numbers.
HTH
Hi

any more info on the relationship between the imaging and guiding scopes and the cameras? mine is an 8" F4.

I'm looking at setting up an autoguider as well. I have a meade 9 x 50 finder and an orion st80.
I won't be visiting dark skies that often so will have to make do with either the finder or the st80.

anybody tried using a light pollution filter for guiding from light polluted areas?
I've been thinking of the qhy5 or the orion st4.

will an adaptor be required to use the cameras with a finder? are there generic 1.25" adaptors to use with the st4 or the qhy5?
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