Optical error where light rays at the lens edge focus differently than at center, creating soft edges.
Spherical Aberration
Spherical aberration is an optical defect where light rays entering the edge of a spherical lens are focused at a different point than rays passing through the center.
Effects
- Wide Aperture: Maximum effect, soft glow
- Narrow Aperture: Minimum effect, sharper image
- Bokeh: SA affects the quality of the blur
Correction
- Aspherical Elements: Non-spherical lens shapes correct SA
- Floating Elements: Movable groups optimize for different distances
- Stopping Down: Visibly reduces SA (but also the amount of light)
Creative Use
Some filmmakers intentionally use SA for a vintage-like look. Lenses like the Helios 44-2 or Canon Dream Lens are known for their characteristic SA glow.
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