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Adjustable-focus eyeglasses. Adjustable focus eyeglasses are eyeglasses with an adjustable focal length. They compensate for refractive errors (such as presbyopia) by providing variable focusing, allowing users to adjust them for desired distance or prescription, or both. Current bifocals and progressive lenses are static, in that the user has ...
Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]
Eyeglass prescription. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an eye examination indicates that corrective lenses are appropriate, the ...
With prices starting at $60 per frame, prescription lenses included, Pair is already pretty affordable. However, for a limited time, Yahoo Life readers can save 15 percent on any Pair Eyewear ...
Rimless eyeglasses are a type of eyeglasses in which the lenses are mounted directly to the bridge or temples. The style is divided into two subtypes: three-piece glasses are composed of lenses mounted to a bridge and two separate temple arms, while rimways (also called cortlands ) feature a supporting arch that connects the temples to the ...
The Nikon F2 is an all-metal, mechanically-controlled (springs, gears, levers), manual focus SLR with manual exposure control. The camera itself needed no batteries, though the prism light meter did (and the motor drive if added). The F2 replaced the Nikon F, adding many new features (a faster 1/2000-second maximum shutter speed, a swing open ...
Nikon F2. The Nikon F camera, introduced in April 1959, [1] was Nikon 's first SLR camera. [2] It was one of the most advanced cameras of its day. Although many of the concepts had already been introduced elsewhere, it was revolutionary in that it was the first to combine them all in one camera. [3] It was produced until October 1973 and was ...
A Fresnel lens ( / ˈfreɪnɛl, - nəl / FRAY-nel, -nəl; / ˈfrɛnɛl, - əl / FREN-el, -əl; or / freɪˈnɛl / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
Subjective refraction. (Top) 0.50 confirmation set; (Middle) trial lens box, including pinhole and occluder; (Bottom) Snellen chart. Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). [1] It is a clinical examination used by orthoptists, optometrists and ...
The OM-1 is an all-mechanical SLR. It has a large viewfinder with interchangeable screens but a fixed prism. It also has a through-the-lens exposure meter controlling a needle visible in the viewfinder. It has a compact body, essentially retained on later models. The shutter speed dial is located around the lens mount, which allows ...