Difference between interference objective and microscope objective
What is the difference between an interference objective and a microscope objective? Recently, many people have consulted me about this question. In this article, I will use simple text and images to illustrate the differences between the two. There are many types of microscope objectives: metallurgical objectives, biological objectives, brightfield/darkfield objectives, fluorescence objectives, differential interference contrast objectives, long working distance objectives, extra-long working distance objectives, plan achromatic objectives, semi-apochromatic objectives, APO objectives, and so on. These all belong to microscope objectives, and their main purpose is to magnify the observed image, i.e., two-dimensional image magnification. Images observed with 10X and 20X microscope objectives are as follows:Photo obtained with a 10X microscope objectivePhoto obtained with a 20X microscope objective The 10X and 20X microscope objectives captured the same sample. From the images, it can be seen that the details observed with the 20X objective are larger than those with the 10X, but the field of view becomes smaller. The higher the magnification, the smaller the field of view. Compared with microscope objectives, interference objectives include a beam splitter and a reference mirror. There are only three types of interference objective structures: LINNIK, Mirau, and Michelson. All three structures include a beam splitter and a reference mirror, which split the light beam inside the lens into two paths: one as the reference path and the other as the measurement path. After the two beams return along their original paths, interference occurs. Microscope objectives, however, do not have a reference path themselves, so they cannot produce interference images. Below is a comparison between an image observed with a microscope objective and an image observed with an interference objective:Image observed with a microscope objectiveImage observed with an interference objective From the images, it can be seen that the image observed with the interference objective has alternating bright and dark fringes. These fringes are interference fringes, and their shape contains information about the surface height of the observed sample. The microscope objective image has no interference fringes, so the surface height distribution information cannot be analyzed from the microscope objective image. If a color camera is used, the fringes will appear in color. Microscope objectives are mainly suitable for observing two-dimensional magnified images, while interference objectives are mainly used to obtain micro-nano level three-dimensional profiles.
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