The vertical-objective-based ellipsometric microscope (VEM) is expected to be a useful method for clarifying the lubrication phenomena that uses thin liquid lubricants, especially the lubricant for hard disk drives (HDDs). Although the feasibility of VEM for thin lubricant films was confirmed, the designs for the optical system and image detection have not been established. In this report, the optical design of the VEM is presented, as well as the method of controlling the coherent noises and improving the thickness resolution is discussed. By our method, the thickness resolution of VEM can be improved to 0.4 nm, and the real-time observation of sub-nm-thick thin liquid lubricant films can also be achieved.