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Ballistic sunglasses or prescription eyeglasses must meet the same requirements. In brief, the U.S. military standard requires that ballistic eyewear must be able to withstand up to a 3.8 mm (.15 caliber) projectile at 195 m/s (640 ft/s)) for spectacles and 5.6 mm (.22 caliber) projectile at 168–171 m/s (550–560 ft/s) for goggles.
A prescription of −1.00 +0.25 × 180 describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D. Only ophthalmologists write prescriptions in + cylinder. An optometrist would write a prescription in - (minus) cylinder. All spectacle and contact lenses would be made in minus cylinder.
Polyvinyl butyral (or PVB) is a resin mostly used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with butyraldehyde.
If a sculpture is broken into several pieces, art conservators may reattach the pieces using an adhesive such as Paraloid B-72 or epoxy. If the sculpture is made of a transparent or semitransparent material (such as glass), the seam where the pieces are attached will usually be much less noticeable if the refractive index of the adhesive ...
Comparison of browline (left) and wayfarer horn-rimmed glasses, with prescription lenses for myopia. A variant of horn-rimmed glasses, browline glasses, became one of the defining eyeglass styles of the 1940s and 1950s. Invented in 1947, the style combined the aesthetics of horn-rimmed glasses with the stability of metal frames by fitting ...
In glasses with powers beyond ±4.00D, the vertex distance can affect the effective power of the glasses. [4] A shorter vertex distance can expand the field of view, but if the vertex distance is too small, the eyelashes will come into contact with the back of the lens, smudging the lens and causing annoyance for the wearer.
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