When your iris changes in size from light why does does the area we can see not change?
In: Biology
Oh, but you can! Do you have an afghan or a loosely knit scarf or something? You know, a piece of fabric that you can see through because it has a whole bunch of small holes?
Cover your eyes with it. I mean right up against your face, so you can see through it. Face a bright light. Even your monitor should work. Now, stare straight forward, close your eyes and count to 5 or 10, then open them up quickly and just keep staring forward. Don’t move your eyes.
If you do it right, you should see all the little holes you’re peering through get smaller for a second, then probably expand again. That’s because your pupils were adjusted to the dark of your closed eyes so they opened up, then they got smaller again from the sudden light.
It’s an example of the [pinhole camera](https://en.wikipedia.org/wiki/Pinhole_camera) effect. The reason the holes you’re looking through look blurry is because they’re not in focus. Each “spot” of light coming through the material is making a blurry circle in your vision. In photography they call these “[circles of confusion](https://en.wikipedia.org/wiki/Circle_of_confusion)” or “[bokeh balls](https://duckduckgo.com/?q=bokeh+balls)”. They’re round because your pupil is round. A small diameter opening will improve the focus by blocking the rays of light at the edges. When your pupils shrink, they create a small opening, causing the light coming through the holes to be more in focus. This causes the out of focus circles of light to decrease in size.
It’s kinda fun to see a real-time indication of your pupil size.
You could also do this experiment using aluminum foil and just poke some holes in it. They can be any smallish size as long as you’re letting enough light through to cause your iris to react to the sudden brightness.
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