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.
During manufacturing, the lens is oversized in diameter. Be aware, forms well behaved within clear aperture may turn exotic or undefined just beyond the final diameter.
Manufacturing Limits for Cylindrical Surfaces Based on Manufacturing Method
Rod or Arbor
|3||Cylinder Radius (mm)||10||∞|
|4||Concave sag to flat (mm)||0.100²||=Radius|
|wdt_ID||Attribute||Asphere Tolerancing Limit|
|1||Glass Quality (nd, vd)||Melt Rebalanced and Controlled|
|2||Diameter (mm)||+0, -0.010|
|3||Center Thickness (mm)⁶||± 0.010|
|4||Sag – Concave (mm)||± 0.010|
|6||Vertex Radius⁸||± 0.1% or 3 HeNe fringes⁹|
|7||Irregularity – Interferometry (HeNe fringes)¹⁰||0.11¹¹|
|8||Irregularity – Profilometry (μm)¹⁰||± 0.5|
|9||Wedge Lens – ETD (mm)||0.002¹²|
|10||Bevels – Face Width @ 45° (mm)¹³||± 0.05|
|11||Scratch – Dig (MIL-PRF-13830B)¹⁴||10 – 5|
|12||Surface Roughness (Å RMS)¹⁵||10|
- This is at minimum radius and width. The part-specific minimum will grow in proportion to radius.
- Flat surfaces lead to scratching problems and polisher contact issues. For both practical and economic reasons consider plano here.