1. Lenses refract light.
2. Convex lenses converge light.
3. Concave lenses diverge light.
4. Focal length measures a lens’s power.
5. Diopters quantify lens power.
6. Lenses form images.
7. Images can be real or virtual.
8. Real images can be projected onto a screen.
9. Virtual images appear behind the lens.
10. Lenses correct refractive errors like nearsightedness and farsightedness.
11. Cameras use lenses to focus light onto a sensor.
12. Telescopes use lenses to magnify distant objects.
13. Microscopes use lenses to magnify tiny objects.
14. Lenses are made of glass or plastic.
15. Lens shape determines its focal length.
16. Aberrations can distort images formed by lenses.
17. Anti-reflective coatings reduce reflections on lenses.
18. Fresnel lenses are thin and lightweight.
19. Contact lenses rest directly on the eye.
20. Zoom lenses have variable focal lengths.

1. Key Light: The primary source of light in a portrait, often placed to the side of the subject to create shadows and dimension.
2. Fill Light: A secondary light used to soften and reduce shadows created by the key light, often placed opposite the key light.
3. Backlight: Positioned behind the subject, it creates a glowing effect around the edges, adding depth and separating the subject from the background.
4. Ratio: The relationship between the key and fill lights, affecting the contrast and mood of the image. Common ratios include 2:1, 3:1, and 4:1.
5. Soft Light: Diffused or softened light that reduces harsh shadows and creates a more flattering, even illumination.
6. Hard Light: Direct and unfiltered light that produces sharp shadows and high contrast, often used for dramatic effects.
7. Natural Light: Utilizes sunlight or ambient light indoors, offering a soft and diffused lighting source, ideal for outdoor portraits.
8. Light Modifiers: Tools like umbrellas, soft boxes, and reflectors that shape and control the quality of light.
9. Exposure: The overall brightness of the image, determined by the combination of aperture, shutter speed, and ISO settings.
10. Direction: The angle and direction from which light hits the subject, influencing the shape and texture of features, as well as the creation of shadows and highlights