Resolved SC-3 short focus knob direction of movement

Discussion in 'Guiding and Adaptive Optics - StarChaser and AO' started by Mark Manner, Feb 16, 2022.

  1. Mark Manner

    Mark Manner Cyanogen Customer

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    Hi, this is a bit of a goofy question. I am working on the install and setup of my new AC4040/AFW/SC-3/AOX, and will be at the remote observatory today in the daylight hours only. I focused the AC4040 last night remotely, and the SC-3 isn't quite at focus. I estimate that it needs to be moved away from the OTA by about 1000 microns to be in focus. I'd like to turn the SC-3 focus knob in the direction that moves its imager away from the OTA by about 1 mm. This will get me a bit closer until I can be there in person at night. Does anyone happen to know which way the focus knob should be turned to go out? I'll guess it is counter clockwise, and test that if no one knows. I can estimate the number of turns by counting how many full revolutions there are stop to stop I suppose (the pick off mirror is about mid-way in, so I calculate that there is about 36mm of movement available, with my system pretty close to the right spot already), but if someone knows that too, that would be helpful. This is probably not going to work well, but won't hurt to try.
    Thanks,
     
  2. Doug

    Doug Staff Member

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    Turning the knob clockwise brings the focus out, turning it counter-clockwise moves it in.

    The motion is very fine - a full turn of the screw moves the focus .031" / 0.8 mm.
     
  3. Mark Manner

    Mark Manner Cyanogen Customer

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    Doug, thanks for the super quick response!
    My guess was wrong as usual :)
    I'll do a 1.25 turn clockwise and see how close I get.
    Best,
     
  4. Colin Haig

    Colin Haig Staff Member

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    It's a bit counter-intuitive. CW draws the sensor assembly away from the pickoff mirror. Instead of turning the bolt into the nut and the bolt gets shorter, what's going on is the "nut" is being pulled toward the bolt head.
     
  5. Mark Manner

    Mark Manner Cyanogen Customer

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    Thanks Colin, I made the adjustment, and tonight I'll see how it works. I'll be there at night next week so I can adjust as needed. I'm enjoying the new camera, thanks for your help during the process.
    Best,
    Mark
     
  6. Mark Manner

    Mark Manner Cyanogen Customer

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    By the way, this worked like a charm! The focus knob is easy to turn accurately, and since I knew the difference in focus position between the main imager and the SC-3, with Doug's information I'm now in focus.
     
    Doug likes this.

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