Depth of fieldvsdepth offocusmicroscope

The objective lens is equivalent to the lens of a projector, and objects are inverted and magnified into a real image through the objective lens; The eyepiece is equivalent to a regular magnifying glass, and the real image formed by the objective lens is then transformed into an upright and magnified virtual image through the eyepiece

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Depth of field microscopeformula

The magnification of the eyepiece is inversely proportional to its length, while the magnification of the objective lens is directly proportional to its length.

Field ofviewmicroscope

The difference between eyepiece and objective lens in optical microscope The eyepiece and objective of a microscope are both convex lenses, with the difference being that the focal length of the eyepiece is shorter,

Depth offocus definition

1. The function of the eyepiece of an optical microscope It is to further enlarge the real image that has been magnified by the objective lens and has a clear resolution, to the extent that the human eye can easily distinguish it.

2. The relationship between the eyepiece and objective lens of an optical microscope. The objective lens has already distinguished the fine structures clearly. If it is not magnified by the eyepiece, it cannot reach the size that the human eye can distinguish, and then it cannot be seen clearly; However, fine structures that cannot be distinguished by the objective lens cannot be seen clearly even after being magnified by a high-power eyepiece. Therefore, the eyepiece can only serve as a magnifying lens and will not improve the resolution of the microscope. Sometimes, although the objective lens can distinguish two objects that are very close together, the distance between the images of these two objects is smaller than the resolution distance of the eye, so it is still difficult to see clearly. So, the eyepiece and objective lens are both interrelated and mutually restrictive.

Eyepiece: Installed at the upper end of the lens barrel, usually with 2-3 pieces, engraved with symbols of 5 ×, 10 ×, or 15 × to indicate its magnification, usually equipped with a 10 × eyepiece Objective lens: Installed on the rotator at the lower end of the lens barrel, there are usually 3-4 objective lenses, among which the shortest one engraved with the "10 ×" symbol is the low magnification lens, the longer one engraved with the "40 ×" symbol is the high magnification lens, and the longest one engraved with the "100 ×" symbol is the oil lens. In addition, a circle of different colored lines is often added to distinguish between the high magnification lens and the oil lens

The depth of focus (DOF) or the focal depth is the range of distances for which the specimen (object) is imaged with an acceptable sharpness on the image plane. DOF is larger as the opening (aperture) angle of the incident probe is smaller but is smaller as the magnification of the image is higher. The opening angle of the incident electron probe of the SEM is about 100 times smaller than that of the optical microscope. Thus, the DOF of the SEM is about 100 times larger than that of the optical microscope. Fig. 1 schematically shows the change in DOF when the diameter of the objective lens aperture is changed. Fig. 2 shows a comparison of SEM images taken at the different DOFs determined by the different objective lens aperture sizes.