Digital Camera Lenses

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Summary
This post delves into the various aspects of digital camera lenses, including their imaging principles, basic functions, and inherent properties such as speed/aperture and focal length. It categorizes lenses into types like standard, wide-angle, telephoto, zoom, macro, and fisheye, discussing their unique characteristics and applications. Additionally, it addresses common lens issues such as flare, perspective distortion, and linear distortion, offering solutions to mitigate these effects. The article also provides guidance on lens cleaning to maintain optimal performance.
  • Convex Lens Imaging Principle: Single focal length determines virtual/real image, double focal length determines size
  • Basic Functions
    • Converge light beams to create image on film
    • Collect large amount of light
  • Inherent Properties
    • Speed/Aperture
      • Amount of light in specific time
        • Maximum aperture
      • Fast lens: More light
      • Slow lens: Less light
    • Focal Length
      • Distance from lens center to digital CMOS where clear image forms
      • Longer focal length:
        • Higher magnification (proportional to focal length)
        • Smaller scene in frame
      • Closer lens to CMOS, stronger light
  • Focus Types
    • Fixed Focus
      • Clear image for objects beyond minimum focus distance
    • Variable Focus
    • Auto Focus
  • Focal Length Categories
    • Longer focal length = Smaller angle of view
    • Larger film requires longer focal length for standard field coverage
      • 35mm format diagonal 50mm, standard lens around 50mm
    • Standard Lens
      • Standard angle of view
        • Matches human visual perspective
    • Wide-angle Lens
      • Wider angle of view
        • Shorter focal length
    • Telephoto Lens
      • Narrower angle of view
        • Longer focal length
          • Expensive
          • Heavy
          • Less stable
            • Shutter speed should be at least 1/focal length(cm) for handheld shots
    • Zoom Lens
      • Disadvantages
        • Expensive
        • Bulky
        • Less sharp than prime lenses
      • Two control rings
        • Focus control
        • Focal length control
      • Best practice: Focus at maximum zoom, then adjust focal length
    • Macro Lens
      • Reproduction ratio
        • Ratio of image size to actual object size
      • Types
        • True macro: 1:1
        • Micro focus: 1:1.2~1:2
        • Close focus: 1:2~1:4
      • Usually medium focal length: 50mm, 100mm
      • Tiny depth of field (1 inch), requires precise focus
  • Lens Issues
    • Flare
      • Bright light reflects off lens surface creating ghosting
      • Solutions
        • Anti-reflective coating
        • Lens hood
    • Perspective Distortion
        1. Objects appear smaller with distance
        1. Less apparent changes with greater lens distance
        • Stronger perspective effect up close
      • Wide-angle perspective distortion
        • Close-up shots exaggerate features (nose appears larger)
      • Telephoto compression
        • Objects appear similar in size at distance
      • Portrait Lens
        • For head-and-shoulders portraits
        • Avoid “big nose” effect from too close
        • Avoid “flat face” effect from too far
        • 85-135mm
          • Maintains proper distance and frame filling while keeping psychological connection
    • Linear Distortion
      • Parallel lines appear non-parallel in tall structures
      • Occurs with all lenses at same angle
      • Solution: Keep camera back parallel to building facade
  • Fisheye Lens
    • Ultra-short focal length, ~180° view angle
    • Lines radiate from center, only center lines remain straight
  • Lens Cleaning
    • Don’t blow on lens surface (saliva droplets)
    • Use professional lens tissue