会社のニュース Aspheric Lenses vs. Spherical Lenses: Differences and Applications

Aspheric Lenses vs. Spherical Lenses: Differences and Applications

Spherical Lenses

Spherical lenses are rotationally symmetric optics whose shape corresponds to a section of a sphere (Fig. 1). The distance from the geometric center to the curvature radius is constant. This means the optically effective surface can be described with a single parameter: the radius R. This uniformity grants spherical lenses significant cost advantages in manufacturing.

Fig. 1: Optically effective area of a spherical surface defined by radius Ra

Manufacturing Advantages

The spherical geometry enables simplified production processes and shorter lead times, especially for small diameters where multiple optics can be fabricated simultaneously on a single substrate. Uniform surface geometry also streamlines optical inspection. Measurement techniques include:

• Tactile methods (profilometers, CMMs)

• Optical methods (interferometers, CGHs)

Applications
Widely used in:

• Metrology

• Aerospace (e.g., satellite spectrometers)

• Medical technology (e.g., slit lamps for eye examinations)
  Their low cost, rapid production, and versatility make them fundamental to optics with excellent price-to-performance ratios.

Optical Performance Optimization

Spherical lenses utilize collecting, dispersing, or focusing properties to refract light. In imaging systems:

• Image quality can be enhanced by adjusting light source position or aperture size.

• Spherical aberration can be reduced via aperture stops that block peripheral rays.

• Multi-lens combinations (e.g., achromats – bonded convex/concave lenses) correct chromatic/spherical aberrations, commonly used in camera lenses.

Aspheric Lenses
Aspherics are ideal for applications demanding:

• High image quality

• Large numerical apertures

• Space minimization
  These rotationally symmetric optics feature radially varying curvature radii (Fig. 2), deviating from spherical profiles to significantly improve imaging performance.

Fig. 2: Comparison of optically effective areas: spherical vs. aspheric surface

Key Characteristics

• Peripheral flattening reduces spherical aberration by ensuring all incident rays converge at a common focal point (Fig. 3).

• Eliminates blur caused by spherical aberration.

• Mathematical surface definition (asphere equation):

• 
• 
• Where:
  $z$ = sagittal height
  $h$ = distance from optical axis
  $R$ = base radius
  $k$ = conic constant
  $A$2i= aspheric coefficients
• 
  
• 

Fig. 3: Spherical aberration correction via aspheric surface

System Miniaturization
Aspherics enable compact optical designs:

• Example: Monolithic beam expanders (e.g., asphericon’s a-BeamExpander) reduce system length by 50% vs. Keplerian/Galilean telescopes (Fig. 5).

• Weight reduction benefits aerospace applications (e.g., Earth observation satellites like Sentinel-4).

Fig. 5: Size comparison: BeamExpander vs. traditional telescopes

Production & Metrology

Modern advances enable high-precision volume manufacturing:

• Methods: Grinding, polishing

• Measurement techniques:

  • CGH interferometry

  • Tactile probing

  • Tilt-wave interferometry (surface topography in 20-30 seconds)

• Digitalized production (e.g., asphericon’s fully automated workflow) reduces costs via batch optimization.

Applications

• Laser systems (beam shaping/expanding)

• Fluorescence microscopy

• Projection systems

• Satellite instrumentation

Final Comparison