Opticians prescribe corrective lenses indicating their powers. Let us say the lens prescribed has a power +4.00 and another has -3.5 D i) What type of lens is the first one? ii) Calculate its focal length. iii) What type of lens is the second one? iv) Find its focal length.
Answers
Answer:
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Step-by-step explanation:
A corrective lens is a lens typically worn in front of the eye to improve vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal, but can be used for purely refractive purposes.
Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lens. Prescriptions typically include the power specifications of each lens (for each eye). Strengths are generally prescribed in quarter-diopter steps (0.25 D) because most people cannot generally distinguish between smaller increments (e.g., eighth-diopter steps / 0.125 D). The use of improper corrective lenses may not be helpful and can even exacerbate binocular vision disorders. Eyecare professionals (optometrists and ophthalmologists) are trained to determine the specific corrective lenses that will provide the clearest, most comfortable and most efficient vision, avoiding double vision and maximizing binocularity.
Single vision lenses correct for only one distance. If they correct for far distance, the person must accommodate to see clearly up close. If the person cannot accommodate, they may need a separate correction for near distances, or else use a multifocal lens (see below).
Reading glasses are single vision lenses designed for near work, and include over the counter glasses. They come in two main styles: full frames, in which the entire lens is made in the reading prescription, and half-eyes, style glasses that sit lower down on the nose.[2] Full frame readers must be removed to see distance clearly, while the distance can be clearly viewed over the top of half-eye readers.
Answer:
i. convex lens
ii. 0.25m
iii. concave lens
iv. -0.28m
Step-by-step explanation:
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