Log Book Entry No.15

Created: 24 Sep 2013 16:55:51

Last Revised: 25 Sep 2013 18:23:27

PedroPaiva

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 0.37µm

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 0.3µm

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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