LENSES

• Lens


  Transparent optical device that manipulates light through refraction
• Lens


  Originates from the Latin word "lenticula," referring to a seed with a shape resembling a lens
• Lenses


  • Have one or more curved surfaces
  • Spherical lenses have at least one spherical surface
• Convex lens


  Thicker in the middle
• Concave lens


  Thicker at the edges
• Convex lens


  Used to correct farsightedness
• Concave lens


  Used to correct nearsightedness
• Optical Center (P)

  The point through which all light rays pass without being bent
• Double concave or double convex lenses

  • The optical center is the geometric center
• Convex Lens - Principal Focus (F)


  Parallel rays falling on the lens are refracted and converge to a point
• Concave Lens - Principal Focus (F)

  Parallel rays falling on the lens spread out, and the refracted rays appear to come from a point in front of the lens
• Focal Length (f)

  The distance from the optical center of the lens to the principal focus
• Thin Lenses

  • The focal points are equidistant from the center of the lens even though the curvature on each side is different
• Secondary Focus (2F)


  The focal point that is twice the distance from the optical center as the principal focus (F)
• Converging Lenses

  • The principal focus (F) is behind the lens, and the secondary focus (F') is in front of it
• Diverging Lenses


  • The principal focus (F) and the secondary focus (F') are in front of and behind the lens, respectively
• Principal Axis


  The line joining the optical center and the principal focus
• • For any object distance from the lens, the image formed by a concave lens is: Virtual, Upright, Smaller than the object, and Located on the same side of the lens as the object.
  • Concave lenses form the same kind of image as convex mirrors.
  • Convex lenses form the same image as concave mirrors.
• • For any object distance from the lens, the image formed by a concave lens is: Virtual, Upright, Smaller than the object, and Located on the same side of the lens as the object.
• • Convex lenses form the same image as concave mirrors.
• • Concave lenses form the same kind of image as convex mirrors.
• • The camera compensates for the eye’s inability to produce permanent records of the images formed in the retina.
• Camera Obscura:

  • The predecessor of the modern camera.
  • A darkened box with a single small opening on one wall and a white projection screen on the opposite wall.
  • Projects an inverted, real image of a brightly lit exterior object onto the white wall.
  • Credited to Arab-Persian scientist Hasan Ibn al-Haytham.
• • In 1826, French inventor Joseph Nicéphore Niépce created the first photographic image using a camera obscura fitted with a lens to project an image onto light-sensitive paper.
• • Both the human eye and the camera process light and record images, but they do it in different ways.
• • When focusing, a camera lens moves to adjust the distance between lens elements/groups and the image sensor.
  • The eye changes shape with the help of ocular muscles to focus on objects at different distances.
• • Both have converging lenses that focus light, but differ in how they adjust to let different amounts of light in.
  • The human eye adjusts the amount of light through the iris, while the camera adjusts the aperture (diaphragm).
• • Human Eye:
  • Processes light and delivers information directly to the brain.
  • Camera:
  • Uses light to record images on a chip, film, or memory card.
• Magnifying Glass


  A converging lens (convex) that produces virtual, upright, and enlarged images of an object placed at a distance less than its focal length
• Using a magnifying glass


  1. Hold close to the eye

  2. Allows a bigger image to be formed on the retina
• Eye's focusing distance


  Can clearly focus on an object at least 25 cm away
• Object placed closer than 25 cm


  Retinal image becomes blurred
• Use of a magnifying glass


  Enables moving the object closer to the eye without requiring the eye to focus closer than 25 cm
• Magnifying glass


  • A short-focused one produces greater magnification than a long-focused one
• • A magnifying glass is often combined with another converging lens to achieve greater magnification.
  • The result is an optical device called a compound microscope.
• Compound microscopes are designed to ensure that the eye is fully relaxed when viewing the final image.
• Eye Relaxation and Image Distance: This relaxation is only possible if the final image is very far from the eyepiece or at infinity.
• Objective and Eyepiece Alignment: This occurs when the first image formed by the objective falls very near the focal point of the eyepiece.
• Magnification: Greater magnification is achieved by using short-focused objective and eyepiece lenses.
• 1. Invention of the Compound Microscope: The compound microscope is credited to the father and son team of Hans and Zacharias Janssen, who invented it in 1590.