What is a Dark Field Microscope?

A dark field microscope is a type of optical microscope, also called an ultramicroscope. A dark field microscope has a light barrier in the center of the condenser, so that the illuminating light does not directly enter the figure, and only the light reflected and diffracted by the specimen is allowed to enter the objective lens. Therefore, the background of the field of view is black and the edges of the object are bright of. With this microscope, particles as small as 4 to 200 nm can be seen, and the resolution can be 50 times higher than that of ordinary microscopes.

Dark field microscope

The basic structure of a dark field microscope is to add a common microscope optical group and a light blocking plate. As long as the condenser is removable, the diameter of the bracket is suitable for installing a dark-field condenser, and it can be converted into a dark-field microscope. When there is no dark field of light, a thick black sheet of paper can be used to make a central shading plate, which is placed under the condenser of a common microscope.

Clinically, dark-field microscopy is often used to examine Pleurocystis. This is an examination of the pathogen and is of great significance for the early diagnosis of syphilis.

Dark-field microscopes are commonly used to observe unstained transparent samples. Because these samples have a refractive index similar to that of the surrounding environment, they are not easy to see clearly in a general bright field of view, so the dark field of view is used to improve the contrast between the sample and the background. This microscope can see particles as small as 4 ~ 200nm. It can only see the existence, movement and surface characteristics of the object, and cannot distinguish the fine structure of the object.

(1) Attach the dark field condenser to the condenser holder of the microscope.

(2) Select a strong light source, but prevent direct light from entering the objective lens, so generally use a microscope lamp for illumination.

(3) A drop of cedar oil should be added between the condenser and the specimen. The purpose is to prevent the illumination light from being totally reflected on the condenser, which will not reach the object to be inspected, and no dark field illumination.

(4) Raise and lower the light collector and aim the focus of the light collecting mirror on the test object, that is, irradiate the test object with the vertex of the cone beam. If the condenser can be moved horizontally and a center adjustment device is attached, the center adjustment should be performed first so that the optical axis of the condenser and the optical axis of the microscope are strictly aligned.

(5) Select the objective lens corresponding to the condenser and adjust the focal length to find the object image to be observed.