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The Donegan OptiVISOR is a hands-free headband binocular magnifier that has optical glass lenses that are ground and polished into prismatic lenses for quality and clarity and is available in multiple dioptric strengths indicated by the number in the model which provide specific magnification power X at specific focal lengths or distance from object. This magnifier enhances the size and resolution of an object or image and is commonly used for a variety of applications such as jewellery-making watch- making needlework artwork electronic inspection book-reading print inspection and stamp-collecting. The OptiVISOR magnifier features replaceable binocular lenses that have bevelled edges that are mounted in an interchangeable plastic frame. An adjustable headband with padded leather comfort band conforms to a variety of head sizes and provides comfort for hours of continuous use. It can be worn over prescription or safety eyeglasses. A durable plastic visor tips up above the forehead when not in use. Spring-loaded pivot screws hold the headband in a raised or a forward-facing position. The magnifier weighs 0.3kg. and comes housed in a protective shell and carrying case. Diopter D is a technical term for the measurement of the light curvature and thickness of a lens. A dioptric number and a magnification number are not the same thing. Diopter strength represents a specific magnification power X. For example a 5-diopter provides 2.5X magnification at a distance of 8. See the magnification chart. The higher the diopter the more magnification a lens can provide. As magnification increases distance to the object focal length and field of view diameter or narrowness of view decreases. Magnifiers and prescription eyeglasses have a diopter value such as 1.5 or 2. The dioptric strength of an accessory lens such as prescription eyeglasses or an eye loupe must be added to the dioptric strength of the magnifier to calculate total magnification. Magnifiers are devices used to enlarge the visual