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Rigel Stepper Motor and usb_nSTEP stepper motor Controller for the TeleVue, Installed on an NP-127 NoN IS

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Rigel Stepper Motor and usb_nSTEP stepper motor Controller for the TeleVue, Installed on an NP-127 NoN “IS”

By Art Morton

Figure 1.

What do I like about it?

It works, the first time, every time

Easy identifiable hardware “comm port” in the “Device Manager”

The usb_nSTEP stepper motor controller works with FocusMax and controls my,

  • RoboFocus Stepper Motor
  • MoonLight Stepper Motor
  • Rigel Systems Stepper Motor

GCUSB_nSTEP software allows me to tune my VCurves in FocusMax

Software and Hardware seamlessly integrated with CCDCommander


Use the Rack and Pinion Original TeleVue Focuser


Try one!

Figure 2.

I have had an adapter with a Crayford Focuser attached to my TeleVue NP-127 for years. It has been wonderful to use for Astro-Imaging. I use a fully unattended platform with CCDCommander which drives FocusMax with a RoboFocus controller.

Figure 3.

One of the challenges I have had with all the Crayfords I have used is that they slip. Not much, but they do slip when the scope is pointed up 30 degrees or higher and I am running it all night from target to target capturing data for LRGB imaging with CCDCommander. So, how do I know this?

The first time I found this problem was calibrating my LRGB filters. First I would autofocus to the L, clear, filter as my reference of zero. Then I would auto focus multiply times with the red, R, filter. The work flow is focus with the L filter, use the position numbers as the zero spot, focus with the R filter, note the focus position. In CCD commander you can the put the new position in as a positive or negative value from your reference focus point. Each time the process was finished, the FocusMax “Position” would indicate a slightly different position of two to eight steps.

Figure 4.

Adjusting the Crayfords(Multiply Manufactures, Multiple Scopes) to the best compromise of “to tight” and “tight enough” to lift and hold in position the SBig ST-8MX with CFW8 can be done, but it is guess work. What I have done, is that I averaged the “position changed” from “reference focus positions” numbers take from 10 runs(which were all different) to provide an average filter offset number. I did the same process for the G,B and HA filters.

Figure 5.

The filters I have are Astronomik or the Original Dichroic RGB SBig filters. These filter sets are described as being Parafocal, by each manufacture. I have yet to meet a set of filters that are exactly Parafocal in my image train setup. However, the measurable differences in focus is not discernible except with the computer focusing with something like the usb-nSTEP/Rigel/reduction gears, integrated with FocusMax/VCurves, CCDSoft(or something like it). I also have a HA filter that is not Parafocal to anything, so FOS or refocusing is a must.

As I stated before, first I adjust my Crayfords so that they are not to tight and not to loose. My adjustment also allows me to manually move(push/pull) the draw tube with the imaging train attached to the start position I uses for my Automated Focusing Process with FocusMax, starting with the L filter.

What I experienced is that with the different temperatures, changes in humidity and mass of the different imaging trains cables ... etc, focus with a Crayford changes.

My example is “Filter Off Set”, FOS. What I discovered from the CCDCommander, CCDC, log data is that the FOS were different between automated focus runs and the different targets over the course of the night. With the OTA and imaging train in different parts of the sky the focus position did change slightly when attempting LRGB imaging, Luminance, Red, Green, Blue, LRGB. The change was not real big, but truly noticeable on the Stars when combining the LRGBHa into a color image.

What did I expect is that I could focus through the L filter once an imaging session, and use that as a reference, as long as the temperatures were relatively unchanged, to FOS the RGB or HA filters. This ended up not being consistently possible with the Crayford focuser and I would get RGB and Ha frames that were out of focus.

The next thing I tried was to move to the target, focus to a reference star with the L filter, close to the target and then uses that new reference focus position as the of set starting point for focus for the FOS settings. This improved the RGB frames but added time to the imaging runs. I still had occasional frames out of focus, and the frames were just slightly out of focus.

To finally resolve this problem, I just used CCDCommander and focused every L, R, G, B frame. This takes a good deal of time. The additonal steps took a lot of time and reduced the targets I had access each night. Focusing takes a good deal more time than the FOS process.

I saw the Rigel TeleVue Stepper, purchase it, replaced my Crayfords with the original stock TeleVue Rack and Pinion focuser. I installation the Rigel Focuser assembly, motor and reduction gears attached to the focuser knob.

What I found when doing my filter characterization reference focusing is that the focus position was the same.

A night of good seeing. The FOS's numbers gathered during automated focusing filer characterization process, were surprisingly consistent for each individual filter, the same position was reported by FocusMax at the end of the run.

The resultant FOS applied to CCDCommander provided consistent, focused RGB frames. The FOS for the HA filters focus position was also spot on. I could now set up the FOSs in CCDCommander and expect to have all the frames captured during the automated process to be focus.

The improvement was the result of the Original Stock TeleVue NP-127 rack and pinion Focuser with the Rigel Stepper Motor for TeleVue Focusers. In combination with the usb_nSTEP one can also get the Temperature Sensor to allow automated Focusing as the temperature goes up or down during an imaging session.

Needless to say, when stopped at a focus position, the focus tube in the TeleVue does not slip when the Rigel's stepper motors gear engaged and the stepper motor coils energized. There are several settings in the usb-nSTEP software to allow the motors and gear to move/lift a Mack Truck(yes this is an over the top statement).

I now have VCurves for TeleVue NP-127 native and the 8” Corrected Newtonian Astro-graph at 1000mm and 762mm. The Rigel System makes it easy to focus when imaging planets with the x2 or x5 TeleVue PowerMates separate or stacked. The Setup Menu allows me to adjust the movement of any of my stepper motors to provide repeatable fine focus. And yes, it works with the current 5.x ASCOM Software Release.

Figure 6.

What I most like about this system is that I can go from a imaging to visual session by just turning the two red thumb screws on the mounting bracket, releasing the reduction gear engagement, so that I can focus by hand.

The installation is simple and looks great. The focus is accurate with FocusMax VCurves. The power consumption works well with battery budget on remote setups. The usb_nStep works with ALL OF MY OTHER STEPPER MOTORS on every OTA's Crayford. What are the “cons”? I let someone else post those.

Software I am using:

  • FocusMax 3.4.30(Image from software created by Larry Webber and Steve Brady)
  • CCDCommander 1.6.33(Image from software created by Matt Thomas)
  • CCDSoft Bisque Software v5.xx
  • MaxIM DL 4.11
  • GCUBB nSTEP 5.0.5
  • Windows XP Pro r3


Mr. Leon Palmer, of Rigel Systems, provided me, the same level of support and responsiveness, I have received from Uncle Al at TeleVue. And that is my story and I am sticking to it. Your milage may vary. I am a satisfied customer.

I do not have a business relationship with TeleVue or Rigel Systems except, I purchased their products and they work!



Figure 7.

Figure 8.

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