The camera is equipped with a XGA OLED Tru-Finder viewfinder that provides high resolution and high contrast, as well as a wide viewing angle. It is designed to with an emphasis to balance its various elements. Therefore, there may be slight distortion near the corners on images seen in the viewfinder because of the 33.3 degree viewing angle and 100% frame coverage. This is normal operation.
You can use the LCD screen if you want to check the details of your picture composition.