Off-axis Guider or Guidescope

[Ian Robinson]

I currently use an old 60mm refractor as my guidescope for guiding my newtonian for prime focus imaging , or side by side with my SLR + telephoto for wide field imaging (on a second smaller GEM).

Works OK , but I am thinking of automating my guiding soon (by acquiring an something like a QGuider) and I am not sure if the rack and pinion and tubes (which are pretty good - tasco 1960s refactors had good focusors) will be up to it , flexure !?!?
This might have important effects in guiding for my newtonian for prime focus long exposure imaging (PEC aside).

So I am considering getting a Lumicon 2" Newt EsyGuider , which needs a bit more back focus (even if it is very low profile).

OK here's the question - will the following arrangement work ?
Seiberb 2" ZeroMagCameraFocusAdapter --> 2" EsyGuider --> Baader MFCC -+ camera .
--> guider

Or should I consider getting a TeleView Paracorr Universial (the photographic one) and the arrangement then becomes :
Seiberb 2" ZeroMagCameraFocusAdapter --> 2" EsyGuider --> Paracorr Uni -+ camera
--> guider
and will it work ?

This would :
1) cut back on the load on my big GEM , no more need for a guidescope.
2) eliminate the guidescope focusor flexure , and guidescope mount flexure issue possibly resulting in much better guiding.

What experience have others here had doing something similar with their fast newts with low profile crayford focusors and heavy (cf guiding eyepieces) autoguiders ?

[Garyh]

Hi Ian,

I am wondering myself that now that I am autoguiding that a OAG would be a good way to go especially with what you are thinking about like the Qguider or like what I was thinking , a DSI.
With 2-3 sec exposures I can`t see that obtaining a guidestar would be a issue myself and this would like you say eliminate flexure and lighten the load on your mount.
It sounds like a good idea but I dont really know how to implement it with my MPCC and maybe a lumicon OAG...
I would be interested in others experiences in this as well
cheers Gary

[Lester]

Hi Ian,

off axis guiders work well, if you can find a suitable guide star within the vacinity of the object being imaged. This is their one and only draw back, that I came across.

[Ian Robinson]

Originally Posted by Garyh

Hi Ian,

I am wondering myself that now that I am autoguiding that a OAG would be a good way to go especially with what you are thinking about like the Qguider or like what I was thinking , a DSI.
With 2-3 sec exposures I can`t see that obtaining a guidestar would be a issue myself and this would like you say eliminate flexure and lighten the load on your mount.
It sounds like a good idea but I dont really know how to implement it with my MPCC and maybe a lumicon OAG...
I would be interested in others experiences in this as well
cheers Gary

Gary - I just emailed Seibert Optical to ask them ... If they reply I'll post their response here . so WTS.

[darrellx (Darrell)]

Hi All

I was wondering if anyone has an update on this issue. I am looking at an oag and so far I have only been able to find two - a meade and the lumicon.

There is a significant difference in price, and I am wondering what most are using.

Thanks
Darrell

[gregbradley]

There are more off axis gudiers. Hutech sells a Mitsuboshi (spelling?) one and Astrodon sells a few variations.

I have a MMOAG (Astrodon) and had a bit of trouble with the setup in that the guide camera wouldn't come to focus. All it needs really is spacers or extender tubes so that the distance from OAG to the camera is the same as from OAG to focal point of the scope.

Greg.

Originally Posted by darrellx

Hi All

I was wondering if anyone has an update on this issue. I am looking at an oag and so far I have only been able to find two - a meade and the lumicon.

There is a significant difference in price, and I am wondering what most are using.

Thanks
Darrell

[TrevorW]

Ian don't know if relevant I use a 10x60 finder with an Orion Starshoot Autoguider and so far have never had a problem finding a guide star to focus on.

Trevor

[Bassnut (Fred)]

Well, for wide field, its unnecessary methinks. Ive done a lot of testing and have seen a fair bit of drama to do with automation (far to much ), your heading for grief with an OAG generally. Also, its expensive to automate OAG rotation to find a guide star, and youll need plate solving and integration with The Sky (or a guide star catalog) to do it properly.

Yes, flexure is a problem, but guide cam focusing isnt, at all. So I bolted my guide cam to the imaging OTA to (almost) eliminate flexure and shift/movement and havent focused for 2 yrs, its irrelivant. Focus once and forget about it.

Unless your doing 15min plus exposures at more than 2m FL and are a precision fanatic, external guiding is MUCH easier, very especially if you want to automate your rig.

[Merlin66 (Ken)]

Late addition to the thread...
I've got ( and sometimes use!) the Meade OAG, Celestron Radial guider,
Lumicon 2" Newt OAG, a no name brand sliding mirror OAG and a Taurus Tracker III.
Although some of these are designed for SCT threads you can easily find a 2" adaptor.
I agree the only problem, (then not really!), is finding a suitable star in the FOV. The TTIII, and Celestron allow good radial movement, by design. My ST4 and/ or the QHY5 guide camera ALWAYS seems to find me a suitable star....
Having said all that. I've also got to admit I've mounted a ST80 on the LX200 and when fitted with the QHY5 works wonders!!!!!!
I comes down to choice. If you want any info on any of the above units, I can supply details.....

[darrellx (Darrell)]

Merlin66

Well, I would still like to give this a shot. In relation to quality how does the Meade and Lumicon compare? When you say "(and sometimes use!)" are you referring to the OAG's generally, or the Meade specifically?

Darrell

[Merlin66 (Ken)]

My main task has been to guide a spectroscope with a 20micron slit on a star image for as long as possible.
I'd prefer using the Celestron or the Lumicon to the Meade. They allow better control of finding and locating a guide star. I find the Celestron easier on the SCT, BUT with the #1209 micro zero shift focuser on the LX200, the Lumicon does a very good job.
I didn't mention, but I'm also testing a Vixen "clone" 50/50 beamsplitter as a guide. This allows full field coverage and "only" costs about 1 magnitude in image brightness. Even with the light loss, it's proving to be very easy and very user friendly.....

[g__day (Matthew)]

If there is any sort of mirror shift or movement happening in your main imaging OTA - then I found OAG is the only reliable way of addressing this. With a sensitive enough guide cam - you should be successful finding a suitable guide star.

[gregbradley]

Originally Posted by Bassnut

Well, for wide field, its unnecessary methinks. Ive done a lot of testing and have seen a fair bit of drama to do with automation (far to much ), your heading for grief with an OAG generally. Also, its expensive to automate OAG rotation to find a guide star, and youll need plate solving and integration with The Sky (or a guide star catalog) to do it properly.

Yes, flexure is a problem, but guide cam focusing isnt, at all. So I bolted my guide cam to the imaging OTA to (almost) eliminate flexure and shift/movement and havent focused for 2 yrs, its irrelivant. Focus once and forget about it.

Unless your doing 15min plus exposures at more than 2m FL and are a precision fanatic, external guiding is MUCH easier, very especially if you want to automate your rig.

I agree with Fred. I have in the past mainly used SBig cameras with their selfguiding which is handy most of the time except for Ha etc.

I now use an external guide scope and camera and its too easy. I never have trouble finding a guide star and the guiding is more accurate not less.

I am imaging at 1260mm focal length.
Greg.