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Aspheres

 

Customers trust Optimax to create high-quality optics and deliver them fast, and our custom aspheres are no exception. Designing with aspheres reduces the size and weight of your system. Optimax produces aspheres from glass, fused silica, crystals and ceramics for UV, Visible and IR applications using proprietary “grind and shine” techniques for low scatter surfaces.

About Aspheric Lens Manufacturing

Aspheres have one or more optical surfaces of non-constant curvature. They are used to manage aberrations inherent to spherical lens systems, and to reduce system size and weight. Aspheric lenses have enabled a leap forward in capabilities for medical devices and defense and security.

Manufacturing and metrology of complex aspheres is an emerging science for optical fabricators: Optimax leads the way in our investment in cutting edge equipment and testing, research and training, and track record of performance on customer programs.

We’ll walk you through the process, and invite you to visit the Resource Library for technical resources at every step.

Specifying Aspheres

Specifying an asphere begins with a custom aspheric form, often fit to the Forbes Q Polynomial (Figure 1) or the Even Aspheric Equation (Figure 2). Describing form involves specifying Vertex Radius (I/C). Conic Constant (k) and applicable Aspheric Coefficients (a). Including a Sag Table (Figure 3) provides reference information to check correct data entry for each manufacturing or metrology tool used.

Forbes Q Polynomial

Asphere Chart Form1

Figure 1
Even Aspheric Equation
Sag Table
Asphere Chart Form2 Asphere Chart Form3
Figure 2

Optimax places tolerances on vertex radius and form error, without tolerances on conic constant or aspheric coefficients. Even aspheric coefficients are preferred.

Need to spec or quote an asphere? Contact us or browse our technical resources:

Specifying, Manufacturing and Measuring Aspheric Lens – Part I and Part II.

Asphere Decision Tree

Manufacturing Aspheres

Looking for the most advanced manufacturing and metrology technology in North America? Optimax utilizes deterministic CNC machine tools for predictable removal rates and adherence to tight tolerances. To control centration, precision tools maintain the optical axis.

Need to spec or quote an asphere? Contact us or browse our technical resources:

Optimax’s Manufacturing Tolerances Chart

Optimax’s Asphere Manufacturing Limits

 

Aspheres Coating Capabilities

Coatings can make or break an asphere’s performance. Optimax offers integrated coating services to reduce the risk and time delay in coating your optics. Our clean environment thin film coating lab has the capability to coat from UV through IR wavelengths. Featuring multiple chambers with deposition sources, including electron-beam and ion assist, Optimax can offer a wide variety of coating options including BBAR, V-coat and mirror coatings. Custom coatings are also available. Coating verification is supported by Perkin-Elmer spectrophotometers.
Coatings Data Sheet
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Testing Aspheres

Optimax inspects 100% of all optics. Test data is provided with prototype orders.

Our metrology must match the sophistication of our manufacturing technology. Optimax offers state-of-the-art metrology, including surface profilers and interferometers to verify that parts meet the form error specification. Testing options are form-specific lenses with mild departure from a best-fit sphere that has the highest potential for fractional wave precision.

Asphere Metrology Matrix

Quality Assurance

Optimax inspects 100% of all optics. Test data is provided with prototype orders. The use of state-of-the-art metrology assures customer satisfaction.

For more information please see Optimax’s Inspection Data Options.

Fast Delivery

Optimax manufactures a wide variety of optical components. When on-time delivery is crucial, Optimax offers an expedited delivery option with a money back guarantee.

Continued Innovation

Optimax’s R&D department is continuously looking for ways to improve our fabrication process and produce higher quality optics. Our current research projects are designed to meet future market needs, such as:

  • Conformal and freeform optics
  • Mid-spatial frequency error-free surfaces

For more information please see Optimax Innovation or contact sales@optimaxsi.com.

Asphere 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
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 accommodated 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

Manufacturing Limits for Freeform Surfaces

Attribute
 Tolerancing Limit*
Diameter (mm) +0, -0.010
Center Thickness (mm) ± 0.050
Irregularity – Interferometry
(HeNe fringes)
0.1**
 Irregularity – Profilometry (μm)  ±1.0
 Wedge Lens – ETD (mm)
 TBD
 Surface Roughness (Å RMS)  10
* Soft Tolerancing Units **Stitching/CGH dependent

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.
  • During manufacturing, the lens is over-sized in diameter.

Manufacturing Limits for Spherical Surfaces

Based on Form Error Tolerance

Attribute
Minimum
Maximum
Diameter (mm) 3 400
Radius (mm) ±1 2
Aspect Ratio (Diameter/Center Thickness) <1:1 30:1
Included Angle (°) 0 2103
1Limited by machine envelope
2Metrology dependent. Avoid 3-10 meter radii when possible, choosing to stay plano instead. It will be less expensive too.
3This represents highest values possible. Actual value possible depends on finished and metrology options available plus tolerance range available for a given part.

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 fabrication becomes more difficult.
  • Certain combinations are unattainable, e.g. 3mm convex radius with 100mm length.
  • Certain configurations add significant fixturing costs, e.g. crossed axis cylinders, cylinders/spheres.
  • Interferometric testing of cylinders is somewhat case specific. Aperture coverage is often limited by the range of diffractive nulls available.
  • Length is always the dimension along the plano axis and width is the dimension across the power axis.

Manufacturing Limits for Cylindrical Surfaces Based on Manufacturing Method

Rod or Arbor
Attribute
Minimum
Maximum
Length (mm) 3 5001
Width (mm) Radius dependent 2 < 2x Radius
Cylinder Radius (mm) – Convex Only 2 150
X-Y
Attribute Minimum Maximum
Length (mm) 3 300
Width (mm) 2 300
Cylinder Radius (mm) 10
Concave sag to flat (mm) 0.1002 =Radius
1This is at minimum radius and width. The part-specific minimum will grow in proportion to radius.
2Flat surfaces lead to scratching problems and polisher contact issues. For both practical and economic reasons consider plano here.

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.

Manufacturing Limits for
Prism Surfaces

Attribute
Minimum
Maximum
Diameter (mm) 3 300
Thickness 1 150
Aspect Ratio1 1 502
1Diameter divided by thickness
2This represents highest values obtained. When at maximum other minimums (irregularity) may not be possible. Will be smaller with less well behaved materials.

Thin Film Coating Manufacturing Limits

Coating Capabilities
Attribute
Minimum
Maximum
Diameter 3mm 500mm
Wavelength 193nm 6000nm
Use Environment Vacuum >95% RH
Durability Moderate abrasion Severe abrasion
Measurement 68°, s, p, average polarization
Laser Damage Threshold 1064nm: >30J/cm2@10ns, >1MW/cm2CW
Layers 1 200
* Soft Tolerancing Units **Stitching/CGH dependent

Above are manufacturing limits and tolerances specific to thin film coating. For more detailed information, please contact sales@optimaxsi.com.

Asphere Tolerancing Limits

General Comments on Tolerancing Limits

  • This represents a general list of soft limits and is intended for reference only.
  • Reducing tolerance range increases costs.
  • Optimax advises a close consideration of budget (tolerance, delivery or dollar) versus need be made prior to choosing any value below.
  • 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 
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.

General Comments on Tolerancing Limits

  • This represents a general list of soft limits and is intended for reference only.
  • Reducing tolerance range increases costs.
  • Optimax advises a close consideration of budget (tolerance, delivery or dollar) versus need be made prior to choosing any value below.
  • Robust sensitivity analyses will help yield the most cost effective tolerancing.

Tolerancing Limits for Spherical Surfaces

Attribute
Sphere Tolerancing Limit
Glass Quality (nd, vd) Melt Rebalanced and Controlled
Diameter (mm) +0, -0.010
Center Thickness (mm)4 ± 0.020 
Sag – Concave (mm)  ± 0.010 
Clear Aperture  100%5
Radius (mm)6 ± 0.0025 or 1 HeNe fringe7
Irregularity (HeNe fringes)8 0.059
Wedge Lens – ETD (mm)  0.00210
Bevels – Face Width @ 45° (mm)  ± 0.0511
Scratch – Dig (MIL-PRF-13830B)12 <10 – 5 
Surface Roughness (Å RMS)  313,14
4This is for the most well behaved materials. More difficult materials (CaF2, Ohara S-FPL, etc.) will need larger tolerances ranges.
5Of full aperture (FA)
6In addition to irregularity
7Whichever is correspondingly larger over the clear aperture
8Coverage dependent, stitched or otherwise, and also subject to system error
9As geometry requirements move closer to a min or max shown the less likely this is possible
10This specification is extremely tight and expensive. For a more economical limit, please consider using 0.005mm.
11Subject to measurement uncertainty
12Crystals and reflective materials will receive 40W inspection
13This represents lowest values obtained. Actual values for crystalline, especially polycrystalline materials, will be higher.
14With scan length and filter appropriate for the selected spatial period.

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 Cylinder Surfaces

Attribute
Cylinder Tolerancing Limit
Glass Quality (nd, vd) Melt Rebalanced and Controlled
Length and width (mm) +0, -0.020
Center Thickness (mm)3 ± 0.020 
Sag – Concave (mm)  ± 0.020 
Clear Aperture  100%4
Radius5 ± 0.1% or 3 HeNe fringes6
Irregularity – Interferometry (HeNe fringes)7 0.18
Irregularity – Profilometry (μm)  ± 0.5 
Plano Axis Wedge – ETD (mm)  0.00512
Cylinder Axis Decentration – TIR (mm)9 0.01010
Axial Twist Angle (arcminutes)  3 
Bevels – Face Width @ 45° (mm)11 0/0mm max
Scratch – Dig (MIL-PRF-13830B)12 10 – 5 
Surface Roughness (Å RMS)13 5 
3This is for the most well behaved materials. More difficult materials (CaF2, Ohara S-FPL, etc.) will need larger tolerance ranges.
4Of full aperture (FA).
5In addition to irregularity.
6Whichever is correspondingly larger over the clear aperture.
7Typical metrology is Zygo MetroPro plots for interferometry.
8As geometry requirements move closer to a min or max shown the less likely this is possible.
9Optimax measures total indicated runout (TIR) as part is rotated. Actual decentration varies with focal length.
10This specification is extremely tight and expensive. For a more economical limit, please consider using 0.0100mm.
11Subject to measurement uncertainty.
12Crystals and reflective materials will receive 40W inspection.
13This represents lowest values obtained. Actual values for crystalline, especially polycrystalline materials, will be higher.

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 Prism Surfaces

Attribute
Prism Tolerancing Limit
Glass Quality (nd, vd) Melt Rebalanced and Controlled
Diameter (mm) +0, -0.010
Center Thickness (mm)3 ± 0.010 
Sag – Concave (mm)  ± 0.010 
Clear Aperture  100%4
Power5 0.1 HeNe fringes6
Irregularity – Interferometry (HeNe fringes)7 0.18
Wedge Prism (window) – ETD (mm)9 0.00210
Bevels – Face Width @ 45° (mm)11 sharp 
Scratch – Dig (MIL-PRF-13830B)12 10 – 5 
Surface Roughness (Å RMS)13 4
3This is for the most well behaved materials. More difficult materials (CaF2, Ohara S-FPL, etc.) will need larger tolerance ranges.
4Of full aperture (FA)
5In addition to irregularity
6This represents lowest values obtained. Will grow with diameter. Will be larger with less well-behaved materials.
7Typical metrology is Zygo MetroPro plot for interferometry.
8This represents lowest values obtained. Will grow with diameter. Will be larger with less well-behaved materials.
9Also known as parallelism or pyramidal error in prism manufacture.
10Tighter specification is possible but can be extremely expensive. For a more economical limit, please consider using 0.005mm.
11Subject to measurement uncertainty
12Crystals and reflective materials will receive 40W inspection
13This represents lowest values obtained. Actual values for crystalline materials, especially polycrystalline, will be higher.

Here are manufacturing limits and tolerances specific to optical aspheres, prisms, cylinders and spheres. For more detailed information on any attribute, please contact sales@optimaxsi.com.

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