The scanning speed and image quality of the digital slide scanner are the two features that users are most concerned about. A real-time focusing configuration centered on a tilted camera is meant to enhance the scanning speed and image quality simultaneously. The device can calculate the defocus distance by taking only one image, and the computation time is only 12.1 ms. Furthermore, based on this, the focal plane can be tracked in real time during the continuous scanning by manipulating the tilted camera and the scanning camera synchronously, which is synchronous focusing and scanning. Synchronous focusing and scanning method saves modeling time and improve the image quality compared with the usual method of modeling first and scanning later.