We describe the scheme and design features of the new IFU unit ( Integral Field Unit ) meant to perform integral-field spectroscopy as a part of SCORPIO-2 focal reducer , which is mounted in the prime focus of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences .
The design of the unit is based on the principle of the formation of array spectra using a lens raster combined with optical fibers .
The unit uses a rectangular raster consisting of 22 \times 22 square 2-mm diameter lenses .
The image of the object is transferred by an optical system with a 23 ^ { \times } magnification from the focal plane of the telescope to the plane of the lens raster .
The image scale is 0 \farcs 75 /lens and the field of view of the instrument has the size of 16 \farcs 5 \times 16 \farcs 5 .
The raster also contains two extra 2 \times 7 lens arrays to acquire the night-sky spectra whose images are offset by \pm 3′ from the center .
Optical fibers are used to transform micropupil images into two pseudoslits located at the IFU collimator entrance .
When operating in the IFU mode a set of volume phase holographic gratings ( VPHG ) provides a spectral range of 4600–7300 Å and a resolution \lambda / \delta \lambda of 1040 to 2800 .
The quantum efficiency of SCORPIO-2 field spectroscopy is 6–13 % depending on the grating employed .
We describe the technique of data acquisition and reduction using IFU unit and report the results of test observations of the Seyfert galaxy Mrk 78 performed on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences .