How an eye focuses.
Why does an image become blurry?
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Why does an image become blurry?
Fit the effective eye lens and inspect the image plane.
The cornea and lens bend incoming light toward an image plane. Vision is sharp when that plane coincides with the retina. Accommodation changes lens curvature to focus objects at different distances.
Thin effective lens combines cornea and crystalline lens; retina position x maps to 10–30 mm behind it. Image distance 1/(1/f−1/do). Focus tolerance 0.7 mm is illustrative.
Focus a nearby object onto the retina.
Focus a sharp image on the retina.