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As distance or the size of the acceptable circle of confusion increases, the depth of field increases; however, increasing the size of the aperture (i.e., reducing f-number) or increasing the focal length reduces the depth of field. Depth of field changes linearly with f-number and circle of confusion, but changes in proportion to the square of ...
In light microscopy, the word aperture may be used with reference to either the condenser (that changes the angle of light onto the specimen field), field iris (that changes the area of illumination on specimens) or possibly objective lens (forms primary images). See Optical microscope.
The points in focus (2) project points onto the image plane (5), but points at different distances (1 and 3) project blurred images, or circles of confusion. Decreasing the aperture size (4) reduces the size of the blur circles for points not in the focused plane, so that the blurring is imperceptible, and all points are within the DOF.
The f-number N is given by: = where f is the focal length, and D is the diameter of the entrance pupil (effective aperture).It is customary to write f-numbers preceded by "f /", which forms a mathematical expression of the entrance pupil's diameter in terms of f and N. [1]
With no modification to the microscope, i.e. with a simple wide field light microscope, the quality of optical sectioning is governed by the same physics as the depth of field effect in photography. For a high numerical aperture lens, equivalent to a wide aperture, the depth of field is small (shallow focus) and gives
Such a blur spot has the same shape as the lens aperture, but for simplicity, is usually treated as if it were circular. In practice, objects at considerably different distances from the camera can still appear sharp; [1] the range of object distances over which objects appear sharp is the depth of field (DoF). The common criterion for ...
Series of images demonstrating a six-image focus bracket of a Tachinid fly. First two images illustrate typical DOF of a single image at f/10 while the third image is the composite of six images. Focus stacking (for extended depth of field) in bright field light microscopy. This example is of a diatom microfossil in diatomaceous earth. Three ...
The three-dimensional point spread functions (a,c) and corresponding modulation transfer functions (b,d) of a wide-field microscope (a,b) and confocal microscope (c,d). In both cases the numerical aperture of the objective is 1.49 and the refractive index of the medium 1.52.