Centration

Glass Quality

Controls: Index and dispersion variation in optical glass

Related Terms: Homogeneity, bubble grade, striae grade, stress birefrigence, international code, 6-digit code

Units: Dimensionless

Specification Must Contain: Nominal value and linear tolerance (Dispersion tolerance typically given a percentage)

Optimax Preferred Specification: Nd and Vd

Reasons: Correlates with international code, information widely available

For More Information

Optimax's Technical Note on Glass Quality

Mechanical Attributes – Diameter, CT and Sag/OAH

Controls: Location of mechanical datums, the distance between optical surfaces or a combination of the two

Related Terms: Center Thickness (CT), Sagitta (Sag), Outside Diameter (OD), Overall Height (OAH)

Units: Linear units

Specification Must Contain: Nominal value and linear tolerance

Optimax Preferred Specification: Directly measured quantities

Reasons: Directly measured quantities offer the best chance for repeatable measurements with minimal error sources

For More Information

Optimax's Technical Note on Mechanical Attributes

Radius

Controls: Radius of curvature of a spherical surface at minimum RMS irregularity, spherical power of a plano surface or vertex radius of asphere

Related Terms: Radius of Curvature, Power

Units: Linear units for radius, wavelengths or half-wavelengths (fringes) for power

Specification Must Contain: Nominal radius value and fringes of power over an aperture or a nominal radius value with linear or percent deviation from nominal over an aperture

Optimax Preferred Specification: Radius deviation for spherical and aspherical, fringes power for plano

Reasons: Radius is directly measured on an interferometer for radii with interferometric coverage or with a profilometer for aspheres and long spherical radii without interferometric coverage

For More Information

Optimax's Technical Note on Radius

Irregularity – Interferometric Measurement

Controls: Form of actual surface relative to perfect form

Related Terms: Form Error, Sphericity, Flatness

Units: Linear units, wavelengths or half-wavelengths (fringes)

Specification Must Contain: Value (RMS, Peak-to-Valley (P-V) or both) over an aperture

Optimax Preferred Specification: P-V surface error in fringes at HeNe

Reasons: Contributors may be directly targeted

For More Information

Optimax's Technical Note on Irregularity

Irregularity – Profilometric Measurement

Controls: Form of actual surface relative to perfect form

Related Terms: Form Error, Rt, Rq

Units: Linear units

Specification Must Contain: Value (RMS, Peak-to-Valley, +/- Sag Error or combination) over an aperture

Optimax Preferred Specification: +/- Sag Error in units of microns

Reasons: Change is relative to nominal form

For More Information

Optimax's Technical Note on Irregularity

Wedge Lens

Controls: Location of once center of curvature relative to some other item. It may be related to another center of curvature, a plane in space, or a physical datum.

Related Terms: Edge Thickness Difference (ETD), Edge Runout (ERO), Wedge, Mechanical Wedge, Total Indicated Runout (TIR), Beam Deviation

Units: Linear units or angular units

Specification Must Contain: Relationship between a center of curvature and the reference.

Optimax Preferred Specification: ETD

Reasons: Directly measured on the machine or with little specialized equipment

For More Information

Optimax's Technical Note on Centration

Bevels

Controls: Intersection of mechanical and optical surfaces. Removes sources of contamination and cosmetic damage.

Related Terms: Breakedge, chamfer

Units: Linear units for a toleranced or a maximum linear dimension, angular units for angles

Specification Must Contain: Width of face and angle, leg length and angle, or only leg lengths

Optimax Preferred Specification: Maximum face width at 45 degrees

Reasons: Directly measured with graduated eye loupe, tooling creates angle

For More Information

Watch for future link on: Optimax's Technical Note on Bevels

Cosmetics

Controls: Quantity and size of local defects within a specific aperture. Local defects could be scratches, pits, broken bubbles, sleeks, scuff marks or coating blemishes.

Related Terms: Scratch-Dig, ISO 10110 Part 7, Defect Grade

Specification Must Contain: Grade to be met under specific grading system

Optimax Preferred Specification: Scratch-Dig per MIL-PRF-13830B

Reasons: Historical familiarity

For More Information

watch for future link on: Optimax's Technical Note on Cosmetics

AR Coating

Controls: Thin films deposited onto optical surfaces used to increase transmission of the surface. AR coatings are matched to requirements of each optic, ranging from the most common and cost effective single-layer MgF2 to custom, multi-band designs specific to a single application

Related Terms: Witness sample (used to test performance), coating durability, adhesion, MIL-C-675C, MIL-F-48616, MIL-C-48497A, MIL-M-13508C

Specifications Must Contain: Wavelength band in linear units, Percent Reflectance or Transmission, Angle of Incidence (if other than normal incidence), and minimum coating aperture (if different than Clear Aperture).

Specifications May Include: Laser Damage Threshold in J/cm²(include Pulse-width, wavelength, repetition rate, spot size), multiple wavelength bands, combinations of R and T specs, polarization requirements.

Optimax Preferred Specification: Average Reflectance, normal incidence

Reasons: Metrology is the most straightforward

For More Information
Optimax's Technical Note on Thin Film Coating

Samples of Standard Coatings Available at Optimax:

Single Layer (l/4 thick) MgF2

- Most cost effective option

- Same coating for all optical glasses

- Performance varies with substrate index