A microscope's field of view refers to the diameter of the circular optical light that is visible when viewing an object under the microscope. Here are the settings on a microscope: Ocular Lens: 10X Low Power Objective Lens: 4X Medium Power Objective Lens: 20X High Power Objective Lens: 30X This image shows the field of view under low power (in millimeters). The microscope field of view, or field diameter, is the distance across the image as seen through the microscope.The field of view is greater at lower magnifications. For example, at 10x magnification 20mm might fill your field of view… … The focal length of a lens defines the lens’s angular field of view. where. The microscope field of view diameter in the plane where the specimen is placed is defined by the following formula:. FN is the field number in millimeters (it refers to the diameter in millimeters of the fixed diaphragm inside the eyepiece; it is usually marked on the eyepiece and sometimes called Field of View … This value forms an inverse relationship with magnification, which means that increasing the magnification results in the reduction of the field of view… For a given sensor size, the shorter the focal length, the wider the angular field … D FV is the diameter of the view field in the specimen plane,. Q. Calculate the field of view … Say for example, you are viewing a material in an optical microscope. In simple terms, field of vision can be defined as the area you see under the microscope for a particular magnification. Examples of Fixed Focus Lenses are many Telecentric Lenses and Microscope Objectives.