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In idealized ray optics, where rays are assumed to converge to a point when perfectly focused, the shape of a defocus blur spot from a lens with a circular aperture is a hard-edged circle of light. A more general blur spot has soft edges due to diffraction and aberrations, [5] [6] and may be non-circular due to the aperture shape. Therefore ...
Optical defocus can result from incorrect corrective lenses or insufficient accommodation, as, e.g., in presbyopia from the aging eye. As said above, light rays from a point source are then not focused to a single point on the retina but are distributed in a little disk of light, called the blur disk.
Defocus; Spherical aberration; Coma; Astigmatism; Field curvature; Image distortion; Although defocus is technically the lowest-order of the optical aberrations, it is usually not considered as a lens aberration, since it can be corrected by moving the lens (or the image plane) to bring the image plane to the optical focus of the lens.
Decreasing the aperture size (4) reduces the size of the blur spots for points not in the focused plane, so that the blurring is imperceptible, and all points are within the DOF. For cameras that can only focus on one object distance at a time, depth of field is the distance between the nearest and the farthest objects that are in acceptably ...
Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. Even in the absence of aberrations, the smallest possible blur circle is the Airy disc caused by diffraction from the optical system's aperture ; diffraction ...
Also, bokeh is not just any blur. To a first approximation, defocus blur is convolution by a uniform disk, a more computationally intensive operation than the "standard" Gaussian blur; the former produces sharp circles around highlights whereas the latter is a much softer effect. Diffraction may alter the
Blur perception plays a key role in focusing on near or far objects. Retinal focus patterns are critical in blur perception as these patterns are composed of distal and proximal retinal defocus. Depending on the object's distance and motion from the observer, these patterns contain a balance and an imbalance of focus in both directions.
Low order aberrations include Myopia (positive defocus), hyperopia (negative defocus), and regular astigmatism. Other lower-order aberrations are non- visually significant aberrations known as first order aberrations, such as prisms and zero-order aberrations (piston).