  Time-series photometry taken from ground-based facilities is improved with
the use of comparison stars due to the short timescales of atmospheric-induced
variability. However, the sky is bright in the thermal infrared (3-5 um), and
the correspondingly small fields-of-view of available detectors make it highly
unusual to have a calibration star in the same field as a science target. Here
we present a new method of obtaining differential photometry by simultaneously
imaging a science target and a calibrator star, separated by <2 amin, onto a
10x10 asec field-of-view detector. We do this by taking advantage of the LBT's
unique binocular design to point the two co-mounted telescopes apart and
simultaneously obtain both targets in three sets of observations. Results
indicate that the achievable scatter in Ls-band (3.3 um) is at the percent
level for bright targets, and possibly better with heavier sampling and
characterization of the systematics.

Instrumentation and Methods for Astrophysics