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Auto guider conundrum

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#1 tma61

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Posted 04 August 2013 - 03:42 PM

I want to purchase a new ccd autoguider and scope for it. I know they are sold as packages. I want to mount it on a AT 6"newt.I have looked at two of thm. One weighs 1.3 lbs and the other 3.0 pounds. The heavier one has a support rail that will fit onto my main tube rings. I think that would take up that weight.Would the 3 pound be too heavy?

Here are the links...oh yes they are both roughly the same cost.

http://www.telescope...Guide-Scope/...

http://www.telescope...toGuider-Ref...

#2 fmhill

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Posted 04 August 2013 - 06:37 PM

Personally the Awesome autoguider is the best choice...

However as far as weight is concerned, you need to add up the weights of all the items in your imaging package and see how it compares to the load rating of your mount. As long as your total weight load is 50% to 75% of the mounts rated load capacity, you will be fine...

#3 tma61

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Posted 04 August 2013 - 08:00 PM

Thank you Mitch

#4 fetoma

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Posted 04 August 2013 - 08:28 PM

Personally the Awesome autoguider is the best choice...


+1 :waytogo:

#5 rigel123

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Posted 04 August 2013 - 09:52 PM

There are quite a few of us on CN that use the Mini Guide Scope set up. I use it with my AT6RC.

#6 *skyguy*

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Posted 04 August 2013 - 10:51 PM

The Awesome autoguider is indeed AWESOME! I use almost the exact same autoguider set up on my 12" SCT. However, I also image at 1940mm focal length.

Using the Awesome autoguider is really overkill when guiding an Astro-Tech 6" f/4 (610mm FL) scope. The Mini 50mm Guide Scope will give you the same results with a weight savings and probably a smaller chance of having flexing problems. No matter how good your mount is ... saving weight is always a good thing! ;)

#7 fmhill

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Posted 05 August 2013 - 03:19 PM

I would point out that an often overlooked factor in selecting an autoguider is the guiding ratio... Some of the best images you will see are made with the autoguider/imaging scopes having a guiding ratio of 1 (unity). This is usually accomplished with a high end camera such as the SBIG ST-4000XCM with dual sensors and fl/pixel size ratio is identical for both guiding and imaging...

However this is not practical for the average amateur astronomer, we use more economical auto-guiding setups consisting of a separate guiding camera and guide scope and live with less than optimum guiding ratios. The rule of thumb is, the closer to unity you can keep the guiding ratio, the higher the guiding quality factor is going to be...

When selecting gear, you can approximate the guiding quality factor by calculating the guiding ratio of the imaging scope focal length & imaging camera pixel size vs the guiding scope focal length & guiding camera pixel size.

Once the gear is in operation to get the quality factor, multiply the RA RMS error times the guiding ratio which gives you a value that can be used to evaluate the expected effective effect of guiding on the images being made... This resulting value is referred to as the guiding quality factor (Q)...

Guide ratio = Ifl/Gfl * Gpx/Ipx

Ifl = imaging scope focal length
Gfl = guide scope focal length
Gpx = guide camera pixel size
Ipx = Imaging Camera pixel size

A good range for the guiding ratio 1 to 6, beyond six may be usable at degraded guiding performance...

#8 budman1961

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Posted 05 August 2013 - 05:17 PM

Try the very same mini 50mm at hayneedle, $79.00

Same exact unit, fast shipping, bought lots of stuff from them.

Andy

#9 GlennLeDrew

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Posted 05 August 2013 - 07:33 PM

A friend uses the Orion SSAG with little 50mm scope on his 14" SCT at f/6.3 to good effect. On a 6" Newt such an optic is more than good enough.

#10 orion69

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Posted 06 August 2013 - 03:18 AM

I would point out that an often overlooked factor in selecting an autoguider is the guiding ratio... Some of the best images you will see are made with the autoguider/imaging scopes having a guiding ratio of 1 (unity). This is usually accomplished with a high end camera such as the SBIG ST-4000XCM with dual sensors and fl/pixel size ratio is identical for both guiding and imaging...

However this is not practical for the average amateur astronomer, we use more economical auto-guiding setups consisting of a separate guiding camera and guide scope and live with less than optimum guiding ratios. The rule of thumb is, the closer to unity you can keep the guiding ratio, the higher the guiding quality factor is going to be...

When selecting gear, you can approximate the guiding quality factor by calculating the guiding ratio of the imaging scope focal length & imaging camera pixel size vs the guiding scope focal length & guiding camera pixel size.

Once the gear is in operation to get the quality factor, multiply the RA RMS error times the guiding ratio which gives you a value that can be used to evaluate the expected effective effect of guiding on the images being made... This resulting value is referred to as the guiding quality factor (Q)...

Guide ratio = Ifl/Gfl * Gpx/Ipx

Ifl = imaging scope focal length
Gfl = guide scope focal length
Gpx = guide camera pixel size
Ipx = Imaging Camera pixel size

A good range for the guiding ratio 1 to 6, beyond six may be usable at degraded guiding performance...


... or just get OAG ...

#11 oo_void

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Posted 06 August 2013 - 08:35 AM

Practicality, I'd go with the Mini (the less weight, the easier to balance).

Bang for the buck though, the Awesome is the better choice. The ST80 alone is a nice scope for the price. When not imaging, it can be a quick GnG. I also use mine for solar and when my daughter comes to Star Parties, it's hers for lunar and bright DSO's.

#12 dawziecat

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Posted 06 August 2013 - 09:32 AM

Guide ratio = Ifl/Gfl * Gpx/Ipx

Ifl = imaging scope focal length
Gfl = guide scope focal length
Gpx = guide camera pixel size
Ipx = Imaging Camera pixel size

A good range for the guiding ratio 1 to 6, beyond six may be usable at degraded guiding performance...


Ouch, Frank! This hurts! :tonofbricks:

The SBIG ST-i Guider kit, with its 100mm 'scope and 7.4 micron pixels isn't much good for anything other than binoculars!

Even with a 530mm FL FSQ the guide ratio is 7.3 with an 8300 chip CCD. :bawling:

#13 fmhill

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Posted 06 August 2013 - 11:46 AM


Guide ratio = Ifl/Gfl * Gpx/Ipx

Ifl = imaging scope focal length
Gfl = guide scope focal length
Gpx = guide camera pixel size
Ipx = Imaging Camera pixel size

A good range for the guiding ratio 1 to 6, beyond six may be usable at degraded guiding performance...


Ouch, Frank! This hurts! :tonofbricks:

The SBIG ST-i Guider kit, with its 100mm 'scope and 7.4 micron pixels isn't much good for anything other than binoculars!

Even with a 530mm FL FSQ the guide ratio is 7.3 with an 8300 chip CCD. :bawling:


The bottom line is, if your getting good images, that is what is important... If it works for you, all is good... 7.3 is less than ideal but still not as bad as some.

I have a friend who purchased the ST-i guiding kit with the 100mm lens, and to date, he's yet to get it working. However I suspect his issues are elsewhere in his setup and we're trying to work through them, mainly a polar alignment issue...

This past winter I purchased a ST-i, received one with a faulty sensor, SBIG replaced it, the one they sent as a replacement is unusable according to their advertized specifications. My intent in purchasing it was to use it for both planetary imaging as well as guiding, however it has way to much noise to be used for either in my application... The future of this replacement camera is presently being debated between the dealer I purchased it from and SBIG...

I suspect the ST-i was developed by SBIG primarily to be used with their OAG and it may work well in that application however marketing it as a general purpose autiguiding camera seems to fall short of the mark from what my experience has been so far...

I'm also testing a ZWO ASI120MM for autoguiding and so far it has impressed me... At present I'm running the ASI120MM on a ED80APO as a autoguiding system mounted piggyback on a EdgeHD 11" on a Losmandy G11 mount, I'm getting PHD reported RA RMS values between 0.06 and 0.18 depending on aiming angle of the mount and am making exposures using 10 minute exposure time.

Substituting my SSAG camera in the same setup and the PHD reported RMS is in the 0.30 to 0.60 range...

My intent is to try the ST-i camera on this same setup, but out terrible weather this summer has curtailed a lot of my planned testing...

One other experiment I have run should interest you. I mounted the ZWO ASI120MM camera on an older Nikkor AI series 105mm f/2.5 lens and mounted on a CG-5 mount with a ED80APO, PHD reported RA RMS values in the 0.03 to 0.04 range for several hours of imaging...

I'd be very interested to hear how your ST-i with 100m lens is working for you...

Thanks for your interest...

#14 fmhill

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Posted 06 August 2013 - 11:59 AM

The OAG has a lot going for it, when set up correctly an OAG will produce very high guiding quality however it is expensive as well as being a PITA to get set up and requires a higher quality guiding camera typically to work well...

The best application for an OAG is in reflector type telescopes that have an issue with main mirror motion. Using an OAG in this application compensates for any mirror motion in the mirror mount...

#15 MattThomas

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Posted 07 August 2013 - 11:01 AM

This past winter I purchased a ST-i, received one with a faulty sensor, SBIG replaced it, the one they sent as a replacement is unusable according to their advertized specifications. My intent in purchasing it was to use it for both planetary imaging as well as guiding, however it has way to much noise to be used for either in my application... The future of this replacement camera is presently being debated between the dealer I purchased it from and SBIG...


Mitch,

Have you contacted technical support here at SBIG regarding your problem? I would certainly be interested in seeing your noisy images that are unusable.

I suspect the ST-i was developed by SBIG primarily to be used with their OAG and it may work well in that application however marketing it as a general purpose autiguiding camera seems to fall short of the mark from what my experience has been so far...


The ST-i and 100mm guiding kit is quite usable. I suggest you take a look at the paper written by Alan Holmes here:
http://www.sbig.com/...ow-about-aut...

Many people are using this combination to successfully guide their system.

Thank you.

#16 GlennLeDrew

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Posted 07 August 2013 - 01:44 PM

As a baseline for assessment... My friend's Meade 14 at f/6.3 is a focal length of 2,240mm. The little 50mm f/3.7-ish guider, at ~190mm f.l., is a ratio of nearly 12:1. Pushing things, to be sure! But the results so far have been vastly better than shooting 30s subs and stacking. The worm on the RA drive even has a very pronounced discontinuity, where the rate suddenly jumps and stars look like doubles, but this is now quelled.

To be sure, greater optical leverage afforded by a larger guide scope is to be preferred! But the power of sub-pixel centroid tracking performed by PHD is sufficiently discriminatory for my friend's imaging needs. And the very lightness of the guider (with cables carefully immobilized) assures minimal flexure, and simplifies counterbalancing.

#17 fmhill

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Posted 07 August 2013 - 02:08 PM

Matt, Suggest you PM me with e-mail address and phone number for further discussions.

Mitch...

#18 jbalsam

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Posted 12 August 2013 - 10:36 AM

I recommend scouring the classified ads for either a guider kit someone is getting rid of (not too common), or the components: a used 80mm f/5 achro (super common), some 100mm or larger guide rings, and an autoguider camera. You should wind up saving about $100 off the cost of that autoguider package.

#19 tma61

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Posted 25 August 2013 - 08:33 PM

Ok, well I bought a second hand SSAG. I know it works and now I'm going to look for a used finder scope and rings that I can convert.

#20 tma61

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Posted 25 August 2013 - 08:42 PM

Try the very same mini 50mm at hayneedle, $79.00

Same exact unit, fast shipping, bought lots of stuff from them.

Andy


Hi Andy, good suggestion but they don't ship to Canada.

Dave ( davewpg) Night Skies Network.






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