B. Weaver, J. Oberling

With trends of the BS OpLev posted here and here, Betsy and I decided to also go out and physically look at where the beam is on the OpLev QPD.  The beam itself sits a little bit low and about half-way to one edge of the QPD.  I've attached a couple of pictures, but they aren't the best quality due to low light and difficult access (the BS OpLev sits on the +X/-Y BSC2 HEPI pier, between the pier and the chamber, roughly 7 feet above the floor).  The 2nd picture is viewing the QPD using an inspection mirror, hence why it is flipped w.r.t. the 1st picture.  My phone camera couldn't really pick out the actual OpLev beam, it instead registered it as a "blob" on the QPD (pointed to by the yellow arrows in each picture); the beam itself is roughly in the center of the blob and looks by my eye to be approximately 1.5mm to 2mm in diameter.  The bright spot seen off to the side in each picture is NOT the beam, it is scatter that is reflecting off of a component on the QPD amplifier board.

Based on this, we decided to NOT recenter the BS OpLev before cartridge removal, as the beam is not near the edge of the QPD.