We have developed a Fabry-Perot imager at the Nasmyth focus of the Communications Research Laboratory (CRL) 1.5 m telescope. The field of view of the camera is 4.0 min x 4.0 min, which is the largest among near-infrared Fabry-Perot imagers. In order to make the velocity shift in the field of view small, we chose a long focal length for the collimator (approximately 470 mm). The accurate parallelism of reflecting surfaces, 5 nm, is achieved by systems including a He-Ne laser and Si photodiodes. This gives an effective finesse of approximately 50. Wavelength calibration is carried out by using a Kr lamp. This calibration includes a correction for wavelength-dependent phase changes in the reflective coatings of the etalon. Using this Fabry-Perot imager, we obtained Br gamma and Pa beta images of the Orion Nebula, including the Bright Bar and a part of the Trapezium. From these images we obtained the distribution of extinction in this area. We found that there are regions with a tendency for the Br gamma/Pa beta intensity ratio to be larger at a place with a larger Br gamma intensity. We conclude that in such regions dust grains exist within the ionized region, causing the extinction.