Magnification and Minification of lenses....pptx

Magnification and Minification of lenses....pptx

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  Magnification and Minification inLenses
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  CONTENTS 1. Magnification inHigh Plus Lenses 3. Comparison and Optical Principles 2. Minification in High Minus Lenses 4. Summary Table
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  1. Magnification inHigh Plus Lenses Overview High plus lenses (convex lenses with positive diopter values) produce magnification of retinal images. This means objects viewed through these lenses appear larger than they actually are.
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  Effects of Magnification Themagnification effect results mostly from relative size magnification, where the image size is increased because of the lens’s converging power. Optical Effects • Reduction in the wearer’s field of view. • “Bug-eye” effect (apparent enlargement of the wearer’s eyes visible to observers). • Relatively narrow field of clear vision through the lens.
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  Design Considerations Lens thicknessand shape contribute to the extent of magnification. Flatter aspheric lens designs can reduce magnification and lens thickness by bringing the back surface of the lens closer to the eye. Visual Distortions • Pincushion distortion. • Surrounding annular blind areas (scotomas) in the peripheral vision, creating challenges in usability and visual comfort.
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  High Plus Prescription Recommendations Lensdesign considerations especially for high plus prescriptions above +8.00 D include aspheric or lenticular designs to minimize thickness and aberrations. Material choice (higher refractive index) can reduce lens thickness but may introduce chromatic aberration. Bringing lenses closer to the eye (short vertex distance) reduces magnification and associated distortions.
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  2. Minification inHigh Minus Lenses Overview High minus lenses (concave lenses with negative diopter values) produce minification, making objects viewed through them appear smaller.
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  Effects of Minification Thereduction in image size occurs because the lens diverges light rays, decreasing the size of the retinal image relative to the actual object. Visual Appearance • The wearer’s eyes appear smaller (sometimes described as “peephole” effect) when observed by others.
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  Design Considerations Minus lensestend to have thinner centers and thicker edges; the thick edges can create lens rings due to internal reflections, which may affect aesthetics. Visual Impact • Minification impacts the wearer’s field of view, potentially reducing peripheral clarity. • High minus lenses can introduce barrel distortion, where straight lines appear curved outward.
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  High Minus LensRecommendations Lens design to reduce minification includes selecting appropriate base curves and using high-index materials to reduce thickness and edge weight. Minimizing vertex distance also reduces minification and enhances visual comfort. Anti-reflective coatings help reduce internal reflections and minimize the "power ring" appearance at the thick edges of minus lenses.
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  3. Comparison and OpticalPrinciples Similarities and Differences Both magnification and minification arise due to the lens power affecting the size of the retinal image; plus lenses converge light rays increasing image size, while minus lenses diverge rays decreasing image size.
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  Challenges Both high plusand minus lenses have challenges in terms of thickness, weight, optical aberrations, and cosmetic appearance. Careful frame selection, lens design (aspheric, lenticular), and material choice (high-index, polycarbonate) are critical in optimizing comfort, appearance, and optical performance for high power lenses. Vertex distance adjustments and minimizing prismatic effects improve visual comfort and reduce unwanted magnification or minification effects.
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  Aspect High PlusLenses High Minus Lenses Lens Type Convex (positive power) Concave (negative power) Effect on Image Magnification (enlarged retinal image) Minification (reduced retinal image) Visual Appearance “Bug-eye” effect (eyes appear larger) “Peephole” effect (eyes appear smaller) Lens Thickness Thick center, thinner edges Thin center, thick edges Optical Distortion Pincushion distortion, blind annular area Barrel distortion Field of View Reduced field of view, peripheral scotomas Reduced peripheral clarity Material/Design Aspheric, lenticular, high index to reduce thickness High index, base curve optimization Vertex Distance Short to reduce magnification and Short to reduce minification and 4. Summary Table
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  Thank You