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Light rays do not exist!

Optics for Career Changers

Dipl. Math. Michael Schäfer
Lensation GmbH, Karlsruhe, Germany


  • Motivation
    Why this title?
    Why this book?
    For whom is this book?
    For whom is this book not?
  • About the Author
    About Lensation GmbH
    Lensation is different
    We have what you are missing – time for lens search


  • Open your eyes! Lenses are everywhere
  • Lens model
  • Comparison entocentrical – telecentrical – pericentrical
  • There’s thousands and thousands of lenses – but why?
    Money reasons
    Project constraints
    Technical developments

Hostile Brothers

Dangerous Half Knowledge

  • Half knowledge about light
    The speed of light is constant and equal for all light colors
    Light does not change its direction within a medium.
  • Half knowledge about Glass
    Glass is transparent
    Every type of glass has a different refractive index
  • Half knowledge about lenses
    Lenses are transparent.
    Lenses for large sensor can also be used on all smaller sensors.
    Opening angle and focal length are equivalent.
    Lenses with the same angle, the same length and focal length have the same FOV.
    The larger the (apparent) iris of a lens, the more light sensitive it is.
    Lenses of the same focal length have the same viewing angle.
    The larger the f-number the larger the depth of field.
    A lens is the more light sensitive, the larger the apparent diameter of the iris.
    An objective can never be “too good”.
    For C-mount lenses, the distance between the flange of the lens thread and the sensor (image plane) is 17.526 mm
    For CS-mount lenses, the distance between the flange of the lens thread and the sensor (image plane) is 12.52 mm
    The length difference between the Back Flange Length of C-mount and CS-mount lens is 5mm
    Lenses change the focal length with the sensor size.
    Fixed focal length lenses have a constant magnification.
    If object and the sensor have the same aspect ratio (eg 4:3), so does the image
    Images of near objects are larger than images of remote objects.
    The physical distance between the object and the sensor determines the aperture angle.


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