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Asphere Limits

Below are manufacturing limits and tolerances specific to aspheric lenses. For more detailed information on any attribute,  please contact sales@optimaxsi.com.

Asphere Manufacturing & Tolerancing Limits

This is a graphical description of some of the terms used below.

General Comments on Manufacturing Limits

  • This represents a general list of soft limits and is intended for reference only.
  • As requirements move closer to a min or max shown the more challenging the part will be.
  • Certain combinations may not be possible – Choosing Max Sag and Min Diameter on concave surfaces for example.
  • Interferometric testing of aspheres is extremely case specific. The slower the onset of departure, the more likely interferometric testing is possible.
  • During manufacturing the lens is oversized in diameter. Be aware, forms well behaved within clear aperture may turn exotic or undefined just beyond final diameter.

Manufacturing Limits for Aspheric Surfaces

Based on Form Error Tolerance

Form Error > 2μm Lower Resolution Profilometry (2-D)1
Attribute
Minimum
Maximum
Diameter (mm) 3 250
Local Radius (mm) -8 (Concave)
Sag (mm) 0 502
Departure (mm) 0.01 20
Included Angle (°) 0 120
Form Error 0.5 – 2μm Higher Resolution Profilometry (2-D)1
Attribute
Minimum
Maximum
Diameter (mm)3 3 250
Local Radius (mm) -12 (Concave)
Sag (mm) 0 252
Departure (mm) 0.01 20
Included Angle (°) 0 150
Form Error < 0.5μm Interferometry with Stitching (3-D)
Attribute
Minimum
Maximum
Diameter (mm)3 3 250
Local Radius (mm) -13 (Concave)
Sag (mm) 0 252,4
Departure (mm) 0.002 1
Included Angle (°) 0 120+5

General Comments on Tolerancing Limits

  • This represents a general list of soft limits and is intended for reference only.
  • Reducing tolerance range increases costs.
  • Robust sensitivity analyses will help yield the most cost effective tolerancing.

Tolerancing Limits for Aspheric Surfaces

Attribute
Asphere Tolerancing Limit
Glass Quality (nd, vd) Melt Rebalanced and Controlled
Diameter (mm) +0, -0.010
Center Thickness (mm)6 ± 0.010 
Sag – Concave (mm)  ± 0.010 
Clear Aperture  100%7
Vertex Radius8 ± 0.1% or 3 HeNe fringes9
Irregularity – Interferometry (HeNe fringes)10 0.111
Irregularity – Profilometry (μm)10 ± 0.5 
Wedge Lens – ETD (mm)  0.00212
Bevels – Face Width @ 45° (mm)13 ± 0.05 
Scratch – Dig (MIL-PRF-13830B)14 10 – 5 
Surface Roughness (Å RMS)15 10 

1Typical metrology is Zygo MetroPro plots for interferometry
2For concave surfaces the maximum may be smaller, limited by tool clearance first. Short radii have lower maximums
3Larger diameters can be accomodated using multiscan fusion
4Total sag allowed is a function of diameter, determined by fringe resolution of the interferometer
5Very basic forms (paraboloid, ellipsoid) can have higher included angles
6This is for the most well behaved materials. More difficult materials (CaF2, Ohara S-FPL, etc) will need larger tolerance ranges
7Of full aperture (FA)
8In addition to irregularity
9Whichever is correspondingly larger over the clear aperture
10A vertex radius tolerance is required in addition to irregularity
11As geometry requirements move closer to a min or max shown the less likely this is possible
12This specification is extremely tight and expensive. For a more economical limit, please consider using 0.005mm.
13Subject to measurement uncertainty
14Crystals and reflective materials will receive 40W inspection
15This represents lowest values obtained. Actual values for crystalline, especially polycrystalline materials, will be higher.