This is the light pattern on the retina, not a picture of what a person experiences.
Change how much light shines on the object.
Balance the light: open wider in dim light, narrow in bright light.
Move the retina card closer to or farther from the lens.
Try it: change one thing at a time
1. Move the retina until the image is as sharp as possible.
2. Turn the light up and open the pupil wide. Can narrowing the pupil bring back detail?
3. Turn the light down to 10%. Compare a small and a wide pupil. Which shows more detail?
4. Make it blurry. Can a smaller pupil make the blur less noticeable?
5. Turn on a few rays. Trace light from the top of the arrow. Where does it land?
How this model works
Light reflected from the object enters the pupil. The focusing lens bends the rays. Light from the top of the object meets below the center, forming an upside-down image.
The retina card catches the sharpest image at one distance. Before or after that distance, rays from each point spread across the card, making blur.
A larger pupil lets in more light, making a dim image easier to detect. A smaller pupil lets in less light and reduces blur from small distance errors. With no light, even the widest pupil cannot make an image visible.
In this model, very bright light with a wide pupil washes out detail. Narrow the pupil to balance the brightness. This white washout is an exaggerated teaching effect, not a literal simulation of a retina or a prediction of what you would see. Real eyes also adjust the sensitivity of their light-sensing cells.
This simplified model uses one lens to stand for the eye's focusing parts (cornea and lens). The flat card represents the curved retina. Distances are model units, not real eye measurements. In real eyes, the pupil responds to light automatically; here you control it. Very small-pupil diffraction, automatic focusing, and brain processing are not simulated. This model does not simulate blindness.