A brief analysis of the focal depth of a microscope
Depth of focus is the abbreviation of depth of focus. That is, when using a microscope, when the focus is on an object, not only all points on the plane at that point can be seen clearly, but also within a certain thickness above and below this plane. Clear, the thickness of this clear part is the depth of focus.
Depth of focus
If the focal depth is large, the entire layer of the object being inspected can be seen, while if the depth of focus is small, only a thin layer of the object being inspected can be seen. The depth of focus has the following relationship with other technical parameters.
1. Focal depth is inversely proportional to the total magnification and the numerical aperture of the objective lens.
2. The depth of focus is large and the resolution is reduced.
Because the depth of field of a low-magnification objective lens is larger, it causes difficulties when taking photos with a low-magnification objective lens. Details will be covered in photomicrography.
Depth of focus: The clearer imaging distance that a point on an object can obtain on the imaging axis behind the lens.
Depth of focus: refers to the distance that the focus (focal plane) is allowed to move along the optical axis of the lens while maintaining a clear image.
Depth of focus: The distance between the retinal images that are conjugate to the depth of field (not very accurate).
Depth of focus (simply put): the clear range of imaging on both sides of the image plane of the lens.
Definition: The focal depth starts in front of the image plane. When it reaches the image plane, the converging light cone forms a minimal circle of confusion. Then the light cone diverges behind the image plane and extends to the same diameter as the beginning of the focal depth. Its depth is very small. Small is only a few hundredths of an inch. Therefore the focusing width provided by the depth of focus is very small.
Factors and rules affecting depth of focus
1. Aperture is inversely proportional to depth of focus. A small aperture means a large depth of focus; a large aperture means a small depth of focus.
2. Photographic distance is inversely proportional to focal depth. The closer the shooting distance is, the greater the depth of focus; the longer the shooting distance is, the smaller the depth of focus is.
Reason: The shooting distance (object distance) decreases, the image distance increases, and the distance between the far and near blur circles increases, so the depth of focus increases.
3. The focal length of the lens is directly proportional to the depth of focus. A lens with a long focal length has a large depth of focus; a lens with a short focal length has a small depth of focus.
Reason: When the shooting distance is constant, the focal length increases and the distance between the far and near blur circles increases, so the depth of focus increases.
4. The depth of focus is proportional to the circle of blur. The larger the permissible circle of blur, the greater the depth of focus; the smaller the permissible circle of blur, the smaller the depth of focus.
