Unit calculator coc6/12/2023 It often may be reasonable to assume that, for whole-image viewing, a final image larger than 8 in × 10 in will be viewed at a distance correspondingly greater than 25 cm, and for which a larger CoC may be acceptable the original-image CoC is then the same as that determined from the standard final-image size and viewing distance. A comfortable viewing distance is also one at which the angle of view is approximately 60° at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8-inch × 10-inch image (for comparison, A4 paper is 8.3 in × 11.7 in, 210 mm × 297 mm US Letter paper is 8.5 in × 11 in, 216 mm × 279 mm). If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision, is approximately 25 cm. With this definition, the CoC limit in the original image (the image on the film or electronic sensor) can be set based on several factors: a print) or on the original image (on film or image sensor). The CoC limit can be specified on a final image (e.g. In photography, the circle of confusion diameter limit ( CoC limit or CoC criterion) is often defined as the largest blur spot that will still be perceived by the human eye as a point, when viewed on a final image from a standard viewing distance. Values of the fraction (e.g., 80%, 90%) vary with application.Ĭircle of confusion diameter limit in photography Suitable definitions often use the concept of encircled energy, the fraction of the total optical energy of the spot that is within the specified diameter. Therefore, the diameter concept needs to be carefully defined in order to be meaningful. A more general blur spot has soft edges due to diffraction and aberrations, and may be non-circular due to the aperture shape. 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. Diffraction effects from wave optics and the finite aperture of a lens determine the circle of least confusion the more general usage of 'circle of confusion' for out-of-focus points can be computed purely in terms of ray (geometric) optics. The term circle of confusion is applied more generally, to the size of the out-of-focus spot to which a lens images an object point. Recognizing that real lenses do not focus all rays perfectly under even the best conditions, the term circle of least confusion is often used for the smallest blur spot a lens can make, for example by picking a best focus position that makes a good compromise between the varying effective focal lengths of different lens zones due to spherical or other aberrations. The smallest circle that they pass through C is called the circle of least confusion.įor describing the blur spot achieved by a lens, at its best focus or more generally. In an imperfect lens L, not all rays pass through a focal point. Two important uses of this term and concept need to be distinguished: The smallest such spot that a lens can produce is often referred to as the circle of least confusion. Real lenses do not focus all rays perfectly, so that even at best focus, a point is imaged as a spot rather than a point. Usages in context include maximum permissible circle of confusion, circle of confusion diameter limit, and the circle of confusion criterion. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. In photography, the circle of confusion is used to determine the depth of field, the part of an image that is acceptably sharp. It is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot. In optics, a circle of confusion (CoC) is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. Diagram showing circles of confusion for point source too close, in focus, and too far
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