The resolution properties of an imaging system are commonly described by its modulation transfer function. The slit and edge methods are the two most commonly used and accepted techniques for measuring the MTF. The use of a slit requires very precise fabrication and alignment of the device in the radiation beam, a high radiation exposure to allow sufficient transmission through the narrow slit (aperture 10 μm). We took notice of the slit aperture and a new slit device with slightly wider aperture (40 μm) was made for the im-provement of the conventional slit device.The aim of this work was to show the properties such as the X-ray tube loading, the alignment and the MTF using the new slit device with slightly wider aperture. Imaging plates in the CR system were employed in this measurement.