Why a larger pupil sees luminous bodies larger
Notebook H optics: the pupil contracts at midday, and the owl's night vision
A pen note on the physiology of vision: all things appear larger at midnight and in the morning than at midday, because the pupil of the eye is much smaller at midday than at any other time. Leonardo argues by comparison with the owl, whose pupil is proportionally larger than a man's, so it gathers more light and sees things larger by night. A small red-chalk figure sits below the first text.
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The pupil's size and the apparent size of things by day and night
All things seen appear larger at midnight and in the morning than at midday, because the eye's pupil is much smaller at midday than at any other time. As the owl's pupil is proportionally larger than a man's, it sees more light by night and sees things larger; at midday it sees nothing unless it contracts that pupil.