Model 01 · Transmission
Bandpass: rays pass through
Exit-angle changes come from the effective optical-thickness profile.
Ray angles exaggerated for visibility
Animated incident rays interact with a filter whose surface-form error changes with the controls.
Imaging consequence
Can the sensor still resolve it?
A Siemens star, fine line pairs, and small lettering expose blur, directional smear, and local distortion sooner than a natural photograph.
Ideal referencePerfect wavefront
Reflected pathRWD 0.00 λ
Bandpass imageTWD 0.00 λ
What changed?
Power defocuses, irregularity distorts locally, and wedge moves the full transmitted image together.
How to read the target
Watch the star’s center, the thinnest line pairs, and the word FLAT. They fail first as wavefront error rises.
Power
Curvature changes focus smoothly.
Power is the best-fit spherical curvature of the nominally flat surface. In reflection, its wavefront contribution follows the doubled optical path and the AOI cosine factor.
RWD = 2 · cos(θ) · flatness
Irregularity
Local errors break the wavefront unevenly.
Irregularity is what remains after power is removed. Neighboring rays see different slopes, so fine structure smears and warps rather than moving as one coherent image.
Total form = power + irregularity
Wedge
Non-parallel faces steer the whole beam.
Wedge primarily changes beam pointing through a plate. It is normally removed as tilt when TWD is reported, so a sharp image can move on the sensor without becoming intrinsically blurry.
δ ≈ α · (n − 1)