BCAM testing

BCAMs are devices for measuring small angular displacements.  We use them to monitor lateral alignment and tip/tilt of DECam with respect to the primary mirror.  Then we can really be sure that DECam is perfectly aligned so that the best possible image quality can be achieved.  Each BCAM (there are four on the Blanco) has one CCD and two red laser diodes.  By imaging pairs of BCAMs, displacements can be inferred.

We performed a test to see if the BCAMs were working.  We recorded the BCAM values as a function of hour angle and constant declination.  If the BCAM values at each positive and negative hour angle are the same, this gives us some confidence that the BCAM values are correct.  Here is a photo of part of the team working on recording the BCAM values.  From front to back is Klaus, Marcelle, David and Claudio.

Now this plot (courtesy optical engineer Roberto Tighe) shows the results.

The x-axis shows the hour angle (in degrees) and the y-axis shows the various BCAM values for the x-, y- and z- angles (which can then be turned into alignment corrections).  At a first glance, the behavior looks normal and gives us confidence that the BCAMs are working.  A more detailed analysis is underway.

We did notice that every once in a while, some anomalous BCAM values were produced.  These unexplainable and unphysical values were discarded from the above figure.  Tonight we will try to isolate instances when the BCAM values are anomalous and try to diagnose this problem.