Slide-out magnifying lens in a plastic case Provides 8-diopter (3X) magnification Optical-grade acrylic lens in plastic frame Protective case acts as magnifier handle when in use Made in USA The Opti-Pak pocket magnifier with sliding case has an acrylic, monocular, optical-grade, prismatic lens, and is available in multiple magnification powers (X) that has a grey body that is shade-coded to indicate magnification abilities such as 3X, 4X, and 5X. This magnifier enhances the size and resolution of an object or image, and is commonly used for a variety of applications such as jewelry-making, watch-making, needlework, artwork, electronic inspection, fly-tying, book-reading, print inspection, and stamp-collecting. The Opti-Pak magnifier features a durable, dustproof plastic case that slides open for use as a handle, and snaps closed to protect the magnifier when not is use. The magnifier fits in trouser pockets, and many purses. A round, monocular lens is housed by a rectangular-shaped plastic, protective perimeter for durability. Its optical-grade lens has been ground and polished into a prismatic lens for clarity. It weighs 0.167 lbs., and comes housed in a protective carrying pouch. 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”). 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) decrease. 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