When your iris changes in size from light why does does the area we can see not change?
In: Biology
Because light travels in all directions at once.
If you shine a flashlight through a hole, you sort of get what you’re talking about. Some light, and a shadow.
But that’s a single source of light moving a single direction.
Your iris is more like the window in your room.
You can go to almost any part of the room and look out the window. But what does “look out the window” really mean? Your eyes don’t emit light, they only receive light. So looking out the window actually means going to a place and observing the light passing through the window and reaching your position. That includes reflected light, so the light bouncing off a car, through the window, and reaching you.
So, say you close your window mostly, leaving just a 6-inch hole in the middle. You can still go to any of the places you could goto before to see out that hole.
The only difference is, now, as you walk around, through this smaller hole, you can see fewer things at a time.
Say, there’s a tree outside your window, a fence further back, and a house even further back.
If used to be, before you covered most of your window, you could stand anywhere in your room pretty much and see the tree, the house, and the fence, all at once.
But, now that you’ve covered most of the window, you can still see everything as you move around, but you see fewer things through the hole at once. Maybe now, from one spot, you can only see some tree leaves, or a section of fence, or a region of house.
That’s mostly what opening and closing the iris does: it allowed your eye to focus.
When your window is very large, as you move about the room, the thing that’s most stable in your vision is t
This is an amazing question!! Good job! Tbh, I don’t even need to know the answer, I just came here to say I am IMPRESSED by your thought process!
Am I the only one who read this as asking about the area of the iris that can been seen?
Camera time! Take an old camera and change the aperture. When you look in the camera, you dont see less from moving the aperture. Not a medical guy so I cant explain the eye, but I do know a camera is just a mechanical eye.
because optics. the size of the it’s does not correspond to the size of the image on the retina.
The retina primarily controls the intensity of light reaching the retina, but has some side effects on sharpness.
Imagine if you held a hole in front of a flashlight. If the hole is very close to the bulb/LED, then it doesn’t really matter how small the hole is (as long as it’s larger than the bulb). The area of light stays the same size because you’re not blocking any light. If you moved the hole further away from the light source, then it starts changing the size of the area.
Similarly, the iris is very close the the focal point, which is where all the light rays converge to a point. Since the light is already concentrated around a tiny point, the size of the iris is always much larger than that point, so light coming from outside of the field of view never would’ve hit your retina regardless of how big your iris was.
Instead, the extra light is coming into the eye from a different angle, but is getting focused to (almost) the same spots in the retina. So instead of getting a wider view, you just get more light.
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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