Focus Sweeps from Sept 16, 2010

• • 3d Plots: 47 Tuc (PDF document, original)

  • 3d Plots: 47 Tuc (PDF document, new -- with both CCDs combined)

Best Focus vs. x,y-Position on Focal Plane

Note: the settings for the tilt/focus box are currently measured to be the following:

A=3.08mm

B=0.93mm

C=0mm

D=3.28mm

Method:

• • Determine the x,y region of best focus for each image of the 47 Tuc focus sweep. E.g., for image 2318, the x,y region of best focus can be found as the 2D "valley" in this 3D plot of star image size vs. x,y-position:

• • Assign the value of the focus position for a given image to all the stars in the x,y region of best focus for that image. Call this the star's "best focus".

  • Combine the above for all the images from the focus sweep.

  • Plot for each star's best focus vs. x,y-position on the focal plane.

Results:

These plots show the "tilt" of the focal plane relative to the current tilt of the tilt/focus box. All of the following four 3d plots are of the same data, but shown at different perspectives. Note that the locus of best focus is approximately planar (but with some curvature). Note that for this night's focus sweep (which only goes out to 8000 microns), most of one CCD has no x,y locus where the stars are in focus. Also note that the gap in "best focus" between 7000 microns and 7500 microns is an artifact of the focus sweep from this night: we took no images between these two focus positions.