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Orion Thin Off-Axis Guider

Orion recently released a new Thin Off-Axis Guider (TOAG) designed with DSLR's in mind.  I had looked at others in the past but felt it was now time to give off-axis guiding a try.  Some of the things that drew me to this guider:

 

  • It is only 10.5 mm wide.  Requirement due to the limited back focus of my Orion 190mm Mak-Newt.
  • I have an Orion StarShoot AutoGuider and description states it was designed for this.  Hoping this would make it easier to use since they are both from the same company.
  • It has M48 threads as I wanted to try and adapt my Hotech Self-Centering Camera T-Adapter for the nose piece.
  • Side-to-side adjustment to aide in finding guide stars.

Unpacking the guider it looked good and I like the finish.  It comes with a number of attachments for use with different optical trains.  The step-down ring (M48 male to T-threads female), was already attached so I removed it. The ring adapter design makes it easier to attached the camera to the TOAG.  The Canon-camera compatible adapter is attached to the camera.  Then this is placed on the TOAG and held in place with thumb screws.  This avoids trying to twist the camera onto the adapter since the guider mount would be in the way.

 

The instructions recommend checking initial focus during the daytime on a distant object.  I must agree this is prudent suggestions as it makes it much easier to changes things, make adjustments, etc.  However, there are a couple of errors or inaccuracies in the instructions.  First there is a reference to Figure 10 and there is no Figure 10.  I also think the instructions would be better with a diagram showing which Allen screws to loosen to adjust the prism and the focus of the autoguider.  Second it is implied that distance from the main camera to the center of the TOAG and the distance from the camera to the center of the TOAG should be the same.  However, if you work on this assumption you will not be able to obtain focus on the autoguider.  

In order to obtain focus the distance between the main camera sensor to the center of the TOAG and the distance between the autoguider sensor and the center of the prism need to be about the same.  For my Canon 60D DSLR this distance is around 49mm.  To get the distance between the autoguider sensor and the prism to be around 49mm a spacer is required.  I used the 5mm spacer from the Orion T-Thread Spacer Ring Kit, (which thankfully I already had) with the Orion StarShoot AutoGuider.  I then loosened the screws close to the autoguider platform to refine the focus by slightly pulling out (about 1mm) the autoguider, (with the main camera in focus).  

You can also add a QHY5L-II with just the included fittings assuming you have the version of the camera with the longer nose piece.  However, later I added a Baader 1.25"/T-2 Eyepiece Holder with Helical Microfocuser from Agena AstroProducts  to hold my QHY5L-II.  

After using this several times I realized the helical focuser really didn't help.  I would have to spend time refocusing everything I get up the guide camera and TOAG.  It is better to use the spacer/screws in the stalk to archive focus one time.  Then each time I set up I just screw the guide camera into the spacer and it is already in focus.

 

However, there is one major issue with this TOAG and that is flex in the stalk assembly.  My first attempt at guiding was not good, in fact using my 50mm Mini guider gave better results in the form of tighter rounder stars.  I determined that the thumb screws on the side, which allow you to slide it back and forth to find a guide star, actually act as a pivot point.  Also where there the stalk goes into the guide platform is a similar problem.  I contact Orion support and sent them a video of the problem.  They seemed to concur that there was an issue and that their engineers knew how to fix it.  They indicated once the fix was available they would send it to me but I got tired of waiting.  Below is an exploded view of the stalk assembly. To fix this I drilled and taped holes in the OTA side of the assembly to add set screws to help stabilize the stalk assembly.

In short the Orion TOAG has a lot of potential to provide an affordable off-axis guiding solution if they will solve the flex/wiggle in the stalk assembly. 

UPDATE:  5-11-2014

A while back, as mentioned above, I contacted Orion support about my concerns with the flex in the stalk.  I even sent them a video of what I was seeing.  They acknowledge the issue and mentioned that their engineers knew how to fix it.  The support representative stated they would put a note in my file and send the fix when it was done.  I was a little skeptical but hopeful.   My hope paid off when a couple of months later I received a package from Orion with new parts for the TOAG.  They upgrade the Canon T-ring so that it holds the DSLR more solidly.  They added new sets screws (at right angles to the original set screws) on the pieces that hold the stalk.  Where I had drilled one new whole they put two new set screws.  This makes a large difference and now the TOAG is extremely solid.  I have used the new TOAG on several different occasions.  There has not been an issue finding guide stars.  The ability to slide the stalk side-to-side does make it easy to find guide stars.  Guiding in both RA and DEC results in very round stars with little tweaking in PHD.  I am very impressed with the updates and I now highly recommend the Orion TOAG!

Pros:

Ring adapter system

Thin and accommodates a number of configurations

Ability to move the stalk side-to-side.  It does help in finding guide stars.

 

Cons:

Errors in instructions