*[[Piezo Calibrations]]
  * Our current objective is a Zeiss 20x 1.0 NA weighing 285g.
  * to calculate the resonant frequency, I think one should just be able to use a [[http://en.wikipedia.org/wiki/Simple_harmonic_oscillator|simple harmonic oscillator]] approximation
    * ''resf=function(k,m) 1/(2*pi)*sqrt(k/m)'' where k is stiffness in N/m and m is mass in kg.
    * For PI 725 series, suggests unloaded mass is ~26g
    * So for out test system with our 285g lens
    * ''resf(.17*1e6,(26+285)/1000)'' ~= 118 Hz which seems close to what we observed (110Hz?) with PI engineer
    * Going with a shorter travel range 100µm positioner would give:
    * ''resf(.23*1e6,(26+285)/1000)'' ~= 137 Hz
    * However moving up to PI-726, stiffness is now 3.4 N/µm (vs 0.23 N/~µm) so resonant frequency is much higher
    * ''resf(3.4*1e6,(69+285)/1000)'' ~= 493 Hz

====== Remaking obective holder ======
As of 2011/06/24 17:17, Steve Scotcher has made 2 pieces to hold the PI-726 PIFOC. 
  * One of them is the plate containing the lens between the main dichroic and the detector dichroic.  This was based on a drawing provided by Rick Ayer from Sutter
  * the second is a horizontal ring with an M38/0.75 ring 
  * both are made from steel

With the PIFOC in place, the objective sits about 14mm lower than it would have done.
Without the PIFOC in place and with the brass M38/0.75 (ext) to M27 (int) adapter which Steve made to fit our Zeiss 20x objective into the PI-726, the objective sits about 7.5 mm lower than with the original adapter.  Working with Steve, I think we might be able to raise the lens by about 5mm. About 1.9mm by moving the plate up to the bottom of the dichroic mirror mount and another 3 or so by making the plate thinner.

Steve has indeed made a slimmer nosepiece and there is now 9mm difference between the original objective height and the current height with PIFOC.  In order to account for this we set the new home for the MP285 to (-4500,-4500,0) i.e. shortening the path length by 9mm.