Large scale focal plane are required by a telescope due to wide field of view with high resolution. Since the detector technology could not accomplish the challenge requirement we developed a focal plane pointing method. This method consists of a pointing mirror and four array detectors.
The pointing mirror is placed between the optics and focal plane. As the mirror turns around the optical axis, the light from optics will be reflected to different direction where detector array is placed in the position of focal plane. The key techniques of this method are the pointing accuracy and stability of the pointing mirror and the flatness of the mosaic detector array. Our preliminary experiments indicate that this method is an effective and feasible way to get a large field of view and high resolution image.