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.

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Orion 190mm Mak-Newt Moonlite focuser install

The Orion 190mm Mak-Newt is a great scope for imaging.  With the corrector plate on front it provides pinpoint stars very nearly to the corners of my Canon 60D DSLR.  Trouble is they are no longer being sold by Orion.  I purchased mine second hand and have used it successfully for a couple of years.  Recently I decided I wanted to upgrade the focuser so that I could do automated focusing using Sequence Generator Pro (SGP).  I selected the Moonlite 2" Model CR Newtonian Focuser (with 2" travel) for several reasons.  First they have a good reputation and I read nothing but good things about them.  Second the authors of SGP use them, (seems like some at Moonlite use SGP), so I knew there would be good software support.  Third Moonlite already has an adapter plate specifically for the Orion 190mm Mak-Newt.


First I removed the old focuser.  I was a little concerned with the dent on the lower left side.  It didn't seem to be an issue with the old focuser as my images showed little camera tilt (analyzed via CCDInspector 2).  The old focuser was attached through screws from the outside.  However, to install the Moonlite I needed to remove the corrector plate as the screws had to be installed from the inside.  First I put painters tape across the seem between the corrector plate and the tube.  I did this to help me align the corrector plate when I went to re-install it,(though collimation would still be necessary).  Then I put the cover back on to protect the outside of the corrector plate during the process.  Next remove the six screws on the tube portion.  Once these are out the corrector plate has to be worked out of the tube.  It is a tight fit so work around the entire edge instead of just just trying to work one side.  Once removed I put the plate in a plastic bag to limit dust, etc. while I installed the focuser.



Front end with the corrector plate removed.









The installation of the Moonlite was a snap.  I ordered it with the the motor and it came pre-assembled with the motor and adapter plate for the Orion 190mm.  The adapter comes with a 1/2" spacer which I didn't need so wasn't used.  If using this for visual work it may be beneficial but since I am doing mainly imaging I need the top of the focuser to be less than about 58mm.  Moonlite provided longer installation screws which are required for my version of OTA.  My version has nipples that the focuser screws screw into from the outside.  The longer screws go up through the holes in the nipples and then into the adapter plate on the focuser.  The screws are stainless steel and so I painted them black to hopefully cut down on reflecting stray light.  The adapter plate seems to be large enough that the dent around the focuser hole doesn't seem to be an issue.  Now to get it under some stars to test it out.


Mount Power/USB distribution hub

Looking at my setup I was always concerned about the number of cables and how they hung off my Orion 190mm OTA and the iEQ45 mount.  Major concern was having a cable snag and rip something out.  Also was some concern that it might be affecting my tracking/guiding.  So I did some searching but references were sparse.  Posed the question on Cloudy Nights  and got some excellent advice and information.  In addition Rudy posted on flicker what he had done in combing the power and USB so that only two cables ran up the mount.  I also found a page on cable organization that provided some good information.  This seemed like a great idea so over the holidays I set out to do the same.

First step was to plan how and what I was going to support.  If I was going to collapse to just two cables, (power & USB) then I needed to support the following out of the hub.

  • 3 USB connections - DSLR, focuser, & guide camera
  • Needed to supply 5v for USB hub.  In past testing a non powered hub would not support the DSLR, guide camera etc. so  need to supply power for a powered hub.
  • Also need to supply 7.5-8v for the DSLR
  • 12v connections for dew, fan, etc.

I ordered two power converters off of eBay.  One is a 12v to 5 v, 3A and the other was a 12v to 7.5, 3A.  I put these into a 5x2.5x2 project box from Radio Shack.  Also used a cigarette lighter adapter from Radio Shack for the power connection.  Issue is it is only 18 awg wire and I will probably have too great of a voltage drop when I want to also power the camera cooler I am building and the dew heater.  So at some point I will probably upgrade this to at least 16 awg wire.  This is the reason for using the wire nuts instead of soldering those connections.

I chose a Kingston 4 port USB hub.  One nice feature is the case is aluminum and so I was able to drill holes in the ends to connect it to the top of the project box.  I did this by first removing the circuit board, (easy to do), so as not to damage it.  After updating drivers I was able to verify that everything would work with it.  I also discovered that some USB cables worked better connecting to it than others.  So if you have issues with your hub try changing cables.

I used four RCA type plugs for the dedicated 12v connections and a mini phono plug for the camera power supply.  I took a Canon power adapter that inserts in the battery bay and cut the non-standard plug off and soldered in a mini phono plug.


Next I needed to mount the power/USB hub to the OTA.  More specifically I ended up mounting to an Orion universal dovetail bar attached to the top of the rings. First I constructed a bracket out of steel I got at Home Depot.  Then painted it with several coats of black paint after washing and drying it to remove any oil on it.



The top of bracket was mounted to the dovetail bar.  I place a rubber bumper on the bottom of the bracket. The bumper was slightly longer than it needed to be so as the tension would help keep the bottom of the bracket snug against the OTA without resorting to drastic measures.  Seems to work pretty well and the box doesn't move at all.


Here are the various cables plugged into the hub.  I took the excess cable and used Velcro cable ties to tie it to the top of the bracket.  This way the excess cable wouldn't flop around as the mount moves.  Also I believe I can keep the bracket and cables mounted to the OTA and thus save time when setting up when I go out to the dark site.   Of course I will need to reattach the cable bundle but it should still save me set up time along with the other benefits.

I then bundled the power and USB cable in a 1/2 cable loom/sleeve and ran it up the counter weight arm.  I then fastened it to the bar holding the rings.  This way when the DEC axis rotates the OTA, weights and the loop out front all rotate in unison.  The loop is large enough clear the DEC motor box etc.  I am also using a powered USB extension, the connector I attached to the end of the counter weight bar so it was out of the way.

When it rotates in RA the counter weight bar can swing taking the bottom loop up.  There is enough slack that it can rotate as far as needed.  The only cable left hanging is the ST4 cable going to the mount from the guide camera.  It would be possible to either just issue the guide commands through ASCOM and thus eliminate the cable or get a longer cable and route it through the bundle.  But for now I will just let it hang.