Aberration

• Aberration (defects)


  Deviations or defects observed in the actual size, position, shape, and colour in the objects formed by single lens

  
• Types of aberrations (defects)

  • Monochromatic aberrations
  • Chromatic aberrations

  
• Aberration (defects)


  Deviations or defects observed in the actual size, position, shape, and colour in the objects formed by single lens

  
• Types of monochromatic aberrations

  • On/off axis
  • Spherical aberration
  • Coma
  • Astigmatism
  • Curvature of field
  • Distortion

  
• Types of aberrations (defects)

  • Monochromatic aberrations
  • Chromatic aberrations

  
• Types of monochromatic aberrations

  • On/off axis
  • Spherical aberration
  • Coma
  • Astigmatism
  • Curvature of field
  • Distortion

  
• Types of chromatic aberrations

  • On/off axis
  • Longitudinal
  • Transversal

  
• Types of chromatic aberrations

  • On/off axis
  • Longitudinal
  • Transversal

  
• Low degree aberrations


  • Myopia
  • Hyperopia
  • Astigmatism
• Low degree aberrations


  • Myopia
  • Hyperopia
  • Astigmatism
• Spherical aberration


  Optical problem that occurs when single wavelength of incoming light rays ends up focusing on different points after passing through a spherical surface

  
• High degree aberrations
• Spherical aberration


  1. Light rays passing through lens near horizontal axis are refracted less than rays closer to edge

  2. Parallel light rays do not converge at same point after passing through lens

  
• Spherical aberration


  Parallel light rays of incoming light do not converge at the same point after passing through the lens

  
• Ways to reduce spherical aberration

  • Using specialized aspherical (non-spherical) lens surface curved outwards to converge light rays into single focal point

  
• Spherical aberration


  • Light rays passing through a lens near its horizontal axis are refracted less than rays closer to the edge or "periphery" of the lens and as a result, end up in different spots across the optical axis

  
• Chromatic aberration


  Optical problem that occurs when different wavelengths of incoming light rays end up focusing on different points after passing through a spherical surface

  
• Types of chromatic aberrations

  • Longitudinal chromatic aberration (on axis)
  • Lateral chromatic aberration (out of axis)

  
• Longitudinal chromatic aberration


  Different wavelengths of color do not converge at same point after passing through lens

  
• Ways to reduce spherical aberration

  Using a specialized aspherical (non-spherical) lens surface, which is curved outwards on one side for the purpose of converging light rays into a single focal point

  
• Lateral chromatic aberration


  Different wavelengths of colour coming at angle focus at different positions along same focal plane

  
• Lateral chromatic aberration cannot be removed by stopping down lens but can be removed or reduced in post-processing software

  
• Chromatic aberration


  Different wavelengths of incoming light rays end up focusing on different points after passing through a spherical surface (converging lens)

  
• Many lenses have both longitudinal and lateral chromatic aberrations present at same time

  
• Ways to reduce chromatic aberrations

  1. Stop down lens (to reduce longitudinal chromatic aberration)

  2. Fix lateral chromatic aberration in post-processing software

  
• Coma


  Type of optical aberration that results in off-axis points of light appearing comet-shaped

  
• Coma damages image permanently and cannot be fixed via post-processing software

  
• Types of chromatic aberrations

  • Longitudinal chromatic aberration (on axis)
  • Lateral chromatic aberration (out of axis)(transverse chromatic aberration)

  
• How to reduce coma

  Stop down lens to smaller aperture
• Oblique astigmatism


  Occurs when rays from off axis point pass through spectacle lenses, causing light to focus as two focal line images (tangential and sagittal)

  
• Longitudinal chromatic aberration


  Different wavelengths of color do not converge at the same point after passing through a lens

  
• Distortions


  Optical distortion caused by lens design, and perspective distortion caused by camera position relative to subject

  
• Lateral chromatic aberration


  Different wavelengths of colour coming at an angle focus at different positions along the same focal plane

  
• Types of optical distortion

  • Barrel distortion
  • Pincushion distortion
  • Mustache/moustache (wavy) distortion

  
• Lateral chromatic aberration cannot be removed by stopping down the lens but can be removed or reduced in post-processing software

  
• Barrel distortion


  Straight lines are curved inwards in shape of barrel, commonly seen on wide angle lenses

  
• Pincushion distortion


  Straight lines are curved outwards from center, commonly seen on telephoto lenses

  
• Many lenses have both longitudinal and lateral chromatic aberrations present at the same time

  
• Mustache/moustache (wavy) distortion


  Combination of barrel and pincushion distortion, straight lines curved inwards towards center then outwards at corners
• Ways to reduce chromatic aberrations

  Stopping down the lens (to reduce longitudinal chromatic aberration) and then fixing lateral chromatic aberration in post-processing software