  We described the design and operation principles of a new tunable-filter
photometer developed for the 1-m telescope of the Special Astrophysical
Observatory of the Russian Academy of Sciences and the 2.5-m telescope of the
Sternberg Astronomical Institute of the Moscow State University. The instrument
is mounted on the scanning Fabry-Perot interferometer operating in the
tunable-filter mode in the spectral range of 460-800 nm with a typical spectral
resolution of about 1.3 nm. It allows one to create images of galactic and
extragalactic nebulae in the emission lines having different excitation
conditions and to carry out diagnostics of the gas ionization state. The main
steps of observations, data calibration, and reduction are illustrated by
examples of different emission-line objects: galactic HII regions, planetary
nebulae, active galaxies with extended filaments, starburst galaxies, and
Perseus galaxy cluster.
