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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]
The prism cover test ( PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
An electronic viewfinder ( EVF) is a camera viewfinder where the image captured by the lens is displayed on a small screen (usually LCD or OLED) which the photographer can look through when composing their shot. [1] It differs from a live preview screen in being smaller and shaded from ambient light, and may also use less power.
The first prosumer camera to use live view for both exposure simulation live preview ES-LV control and live preview framing was the fixed-lens Canon PowerShot G1 from 2000 (possibly the first was Canon Powershot Pro70 in 1998), although this was still in the line of compact cameras. The first DSLR to use live view for framing preview only, like ...
Fixation disparity. Fixation disparity is a tendency of the eyes to drift in the direction of the heterophoria. While the heterophoria refers to a fusion-free vergence state, the fixation disparity refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. [1]
Prism (optics) An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base and rectangular sides.
Reflex finder. A reflex finder is a viewfinder system with a mirror placed behind a lens. The light passing through the lens is reflected by the mirror to a focusing screen, usually ground glass. The image formed on this ground glass can be observed directly, giving a waist-level reflex finder, or through a redressing optical device (set of ...
Some of the improvements the D90 offers over the D80 include 12.3 megapixel resolution, extended light sensitivity capabilities, live view and automatic correction of lateral chromatic aberration. The D90 is the first DSLR to offer video recording, with the ability to record HD 720p videos, with mono sound, at 24 frames per second.