Filter Angle Shift Calculator
Calculate the wavelength shift of interference filters due to angle of incidence. Supports both collimated beams (fixed AOI) and convergent beams (f-number).
Interference filters — bandpass, longpass, notch, and dichroic designs — are fabricated for normal incidence. Tilting the filter or using it in a convergent beam shifts its center wavelength toward shorter wavelengths according to λ(θ) = λ₀ √(1 − sin²θ / n_eff²), where n_eff is the effective refractive index of the filter stack (typically 1.5–2.1 depending on coating design). This tool handles two cases. In Collimated Beam mode, a single angle of incidence (0–30°) is applied uniformly and the tool returns the shifted center wavelength and shift magnitude. In Convergent Beam mode, a beam f-number defines the cone half-angle, producing both a net blueshift of the effective passband center and a broadening of the passband — both effects degrade spectral selectivity. Use it to anticipate filter performance in tilted or focused-beam configurations.