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Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks
Diffraction is an optical effect which limits the total resolution of your photography — no matter how many megapixels your camera may have. It happens because light begins to disperse or "diffract" when passing through a small opening (such as your camera's aperture). This effect is normally negligible, since smaller apertures often improve sharpness by minimizing lens aberrations. However, for sufficiently small apertures, this strategy becomes counterproductive — at which point your camera is said to have become diffraction limited. Knowing this limit can help maximize detail, and avoid an unnecessarily long exposure or high ISO speed. Light rays passing through a small aperture will begin to diverge and interfere with one another. Large Aperture Small Aperture Since the divergent rays now travel different distances, some move out of phase and begin to interfere with each other — adding in some places and partially or completely canceling out in others. Diffraction Pattern Airy Disk

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Photon Nomenclature[edit] In 1900, Max Planck was working on black-body radiation and suggested that the energy in electromagnetic waves could only be released in "packets" of energy. In his 1901 article [4] in Annalen der Physik he called these packets "energy elements". Understanding Lens Diffraction This is not a comprehensive treatise on the subject of lens diffraction effects. Rather, it's purpose is to bring to the attention of photographers who may not be aware of the issue that there is no free lunch when it comes to achieving greater depth of field though stopping down. Every photographer wants both maximum resolution and maximum depth of field. But unfortunately these two demands can be mutually exclusive. As you stop down the aperture on a lens the light passing through tends to diffract, reducing sharpness, though DOF is increased.

Lens Genealogy LENS GENEALOGY Part 1by Roger Cicala Where do new lens designs come from?I knew that today’s lenses are all designed using computer programs, but I was surprised to find new lenses aren’t designed from scratch. DSLR Magnification By: Nick Rains We live in ‘interesting times’. Not since colour film was introduced has so much controversy raged about photography. The Internet has allowed vast global discussions to ebb and flow like never before and whilst this is great in some respects, the downside is that there is a whole lot of misinformation floating around. Problem: How to sift the simple facts and truths from the myths and rumours? Answer: With a basic knowledge of certain aspects of photography, especially basic lens theory.

TAMPL SUMMER 97 Several different optical phenomena are studied through the Microscale Reflectance Spectrometer: Thin-Film Interference occurs only in the presence of thin-films. The required condition is that the thickness of the film is on the same order of magnitude as the wavelength of incident light. Diffractionoccurs when there are surface roughness with regular patterns. Circle of confusion In photography, the circle of confusion (“CoC”) is used to determine the depth of field, the part of an image that is acceptably sharp. 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. Properly, this is the maximum permissible circle of confusion, the circle of confusion diameter limit, or the circle of confusion criterion, but is often informally called simply the circle of 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. The smallest such spot that a lens can produce is often referred to as the circle of least confusion.

Depth of field and diffraction Understanding image sharpness part 6:Depth of field and diffractionby Norman Koren updated Nov. 5, 2004 In this pagr we discuss depth of field (DOF) and deal with such questions as, How sharp is the image at the DOF limits? Depth of field and your digital camera What is depth of field? A photographic lens renders a sharp image of points at one given distance, measured along the lens axis. This distance can be adjusted (the process of focusing). Any points at a different distance will be rendered more or less unsharp, and this unsharpness increases gradually as we move away from the "sharp" focus plane.

Sunny 16 rule The basic rule is, "On a sunny day set aperture to f/16 and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting] for a subject in direct sunlight."[1] For example: Lens speed A fast prime (fixed focal length) lens, the Canon 50mm f/1.4 (left), and a slower zoom lens, the Canon 18–55mm f/3.5–5.6 (right); this lens is faster at 18mm than it is at 55mm. Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it delivers more light intensity (illuminance) to the focal plane, achieving the same exposure with a faster shutter speed. A smaller maximum aperture (larger minimum f-number) is "slow" because it delivers less light intensity and requires a slower shutter speed. A lens may be referred to as "fast" or "slow" depending on its maximum aperture compared to other lenses of similar focal length designed for a similar film format.

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