The tolerance in Optical Design

1. Radius (Surface Accuracy)

• Refers to the measurement accuracy of test plates. Optical designers should communicate with optical fabricators.

2. Power Matching (Fringes)

• 1 fringe ≈ ½ wavelength of sagitta-induced radius change.

• Standard fabrication: ≤5 fringes

• Precision fabrication: ≤3 fringes

• Formula: Z=(2λ)⋅N

3. Surface Irregularity

• Evaluated via local fringes.

• Achievable precision: 0.3 fringes.

4. Thickness/Spacing

• Includes optical element thickness and mechanical spacer gaps.

• Zemax simulation:

• Nominal thicknesses: Surface 3 (BK7) = 3mm, Surface 4 (F2) = 4mm, Surface 5 (Air) = 6mm.

• If TTHI on Surface 3 = +0.1mm:

• Adjusted thicknesses: 3.1mm (BK7), 4.0mm (F2), 5.9mm (Air).

• Absolute position from Surface 6 to image plane remains unchanged.

• Int1 = Surface to tolerance

• Int2 = Compensating surface

• Min/Max = Deviation in lens units (mm)

• TTHI operand:

• Example:

5. Wedge/Concentricity/Tilt

• Wedge angle = Edge thickness difference (2δ) / Diameter (D) (in radians).

• Zemax simulation:

• Example: TIR=0.10mm → +0.05mm (min +X) and -0.05mm (min -X).

• TIRX/TIRY: Simulates Total Indicator Runout (TIR).

• TETX/TETY: Tilts any surface (standard/non-standard).

• TSTX/TSTY: Tilts standard surfaces only.

• To tilt a single surface: Set Int1 = Int2 = Surface number.

6. Decentration

• Two types:

1. Lateral shift (up/down).

2. **"Roll"** (maintaining contact with mount).

• Zemax simulation:

• Int1/Int2 define the boundary surfaces of a lens group.

• TSDX/TSDY: Decenters standard surfaces (units: mm).

• TEDX/TEDY: Decenters elements (standard/non-standard).