In this study, details of the intensity calibration of Dual Etalon Fabry-Perot Optical Spectrometer (DEFPOS) were described. At TUBITAK National Observatory (TUG), The DEFPOS was redesigned so as to observe galactic H alpha emission line from the diffuse ionized gas with 4' field of view (FOV) and then was located at the coud, exit of the 150 cm RTT150 telescope (angstrom zahan et al., Research in Astronomy and Astrophysics (RAA) 9(2), 2009). The Absolute intensity calibration of the spectrometer was made by utilizing the data obtained from nine selected regions of NGC 7000 nebula. These regions were selected within 49' FOV whose intensity calibration was determined to be 850 +/- 50 R by Scherb (Astrophys J 243:644-650, 1981). One of these regions was specially selected because of its intensity for the 4' FOV was estimated as 900 R by Morgenthaler et al. (Astrophys J 563(1):451-461, 2001). For calibration of the DEFPOS data, the intensity values from Ishida and Kawajiri (PASJ 20:95-121, 1968) and the VTSS H alpha maps were used and it was found that 1 ADU km s (-aEuro parts per thousand 1) equals 2337.4 R for a 1200 s exposure time. The radial velocities and the line widths from these regions were also determined and compared with the previous results. These calibrations have been in close agreement.