  We report the design concept and performance of a compact, light-weight, and
economic imaging polarimeter, TRIPOL (the Triple Range Imager and POLarimeter),
capable of simultaneous optical imagery and polarimetry. TRIPOL splits the beam
from wavelength 400 to 830 nm into g'-, r'-, and i'-bands with two dichroic
mirrors, and measures polarization with an achromatic half-waveplate and a
wire-grid. The simultaneity makes TRIPOL a useful tool for small telescopes for
photometry and polarimetry of time variable and wavelength dependent phenomena.
TRIPOL is devised for a Cassegrain telescope of an aperture of ~1 m. This paper
presents the engineering considerations of TRIPOL and compares the expected
with the observed performance. Using the Lulin 1-m telescope and 100 seconds
integration, the limiting magnitudes are g' ~ 19.0 mag, r' ~ 18.5 mag and i' ~
18.0 mag with a signal-to-noise of 10, in agreement with design expectation.
The instrumental polarization is measured to be ~ 0.3% at three bands. Two
applications, one to the star-forming cloud IC 5146, and the other to the young
variable GM Cep, are presented as demonstration.
