Log Book Entry No.15

Days, Calendar Created: 24 Sep 2013 16:55:51 Days, Calendar Last Revised: 25 Sep 2013 18:23:27 Person PedroPaiva Text Focus Study (Pt I)

Focus movements

  • Positive -> In
  • Negative -> Out

Tests
The data below have a significant experimental error associated with the not fixed measuring equipment.
Also, they can have errors related to a possible angle between the measuring equipment and the in-out axis therefore, the real value would differ by a factor of cos(theta)

out

  • move(-5000) - 1.86mm
  • move(-5000) - 1.80mm
  • move(-5000) - 1.86mm
  • move(-5000) - 1.81mm
  • move(-5000) - 1.88mm
  • mean = (1.842 ▒ 0.031)mm

  • move(-1000) - 0.31mm
  • move(-1000) - 0.40mm
  • move(-1000) - 0.44mm
  • move(-1000) - 0.27mm
  • move(-1000) - 0.45mm
  • mean = (0.378 ▒ 0.076)mm

The out movement is coherent and 5000 steps is indeed equivalent to 5x1000 steps
This give 1 step aprox 0.37Ám

in

  • move(5000) - 1.52mm
  • move(5000) - 1.55mm
  • move(5000) - 1.52mm
  • move(5000) - 1.48mm
  • move(5000) - 1.57mm
  • mean = (1.528 ▒ 0.031)mm

  • move(1000) - 0.21mm
  • move(1000) - 0.20mm
  • move(1000) - 0.15mm
  • move(1000) - 0.30mm
  • move(1000) - 0.18mm
  • mean = (0.208 ▒ 0.050)mm

The in movement is 25 to 50% smaller than the out movement (depending on the movement size) with larger movements closer to the equivalent out.
This give 1 step being between 0.2 and 0.3Ám

Conclusions
The execution of the above movements led to the following conclusions:

  • Focuser always finishes in a 'in-movement' (e.g. asking to move out will make the focuser goes more than needed and come back about 1mm)
  • This causes the isMoving check to return before the focus being ready.

  • Focuser limit less than aprox 30k steps when going in.
  • When close to the limit, focuser will overstep (move(5000) caused the focuser to move 2.76mm)

  • Focuser isn't ready when isMoving returns False.
  • There's a time gap when a second comand will be accepted but not executed.

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Subject Focus Study (Pt I)
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Topic revision: r3 - 25 Sep 2013 - PedroPaiva

 
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