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I tried the finger trick on some small print and it works! This would be even better if the physics behind it was explained? Interference comes readily to mind, but doesn’t explain anything to me?
Any help?
I prefer beer goggles.
When you close up an aperture, it creates a “lensing” effect. In old days, some painters would use the camera obscura to focus an image on the back of the box. The box could hold an adult, and the image was inverted. The pupil of the eye does the same thing but have the brain to make the image normal (at least normal for the ones who have some brain function, politicians are not included.)
I’ve made many pinhole cameras with 126 film (gone the way of the dodo) and even made a photograph of my grandfather that wasn’t bad for a 10 year old.
I have one eye where I suffered a detached retina. The doctor has a device that covers the eye but has pin holes. I have to look through it every visit and read an eye chart. I can attest that it works. Without the pin holes I can hardly read the E at the top. With the pin hole I can read pretty far down the chart.
Stopping down a camera, i.e. using a smaller aperture, creates more depth of field for the same reason.
Funny though, when I read the title, I was expecting the Joo Janta 200 Super-Chromatic Peril-Sensitive Sunglasses that go completely opaque when danger is present, this shielding the wearer from knowledge of the danger, from the Hitchhiker’s Guide to the Galaxy, of course.
Well, I’ve googled “pin hole camera” just a bit and caught some interesting detail.
I understand the rectilinear propagation of light and how the image is formed–what I can’t find is how it corrects my faulty vision which should see “everything” as out of focus?
Now that’s interesting. I tried this myself and it works, even if you wear strong glasses! Maybe this is related to people’s incentive to squint if they can’t see something?
I’d definately like to learn how this works.
Here’s a starting point for light passing through a pinhole and why it works for a camera. Basically, only roughly parallel light rays pass through the pinhole, thus focusing the light onto a planar surface some distance behind the hole.
From “Practical Physics” –.
http://tinyurl.com/3xfm2j
It increases the depth of field (focus distance) at the retina.
Didn’t this guy used to be on the Red Green Show?
Being quite myopic, I found this trick (both the pinhole and the finger trick) when I was 8 or so. To me it seems like common knowledge.
yeah ive known about this for a LONG time, doesnt make it any less cool tho
The smaller the hole (aperture), the more the light rays are in parallel, Conversely, the larger the aperture, the more diffuse the rays are to each other. The diffuse rays of a large aperture will focus in a small range. The more parallel the rays, the longer the focus point.
Our eyes generally have a large aperture. The light entering must focus to an exact spot by the eye lens. When the lens can’t bend enough to focus the light to the back of the eye due to age, injury, misshaped eye, or other problem, the image will appear out of focus. This is because the eye lens is focusing either behind the receptors or in front of the receptors. When the light rays entering the eye are parallel, there is a bigger range to put them into focus.
Most of the body organs like things in a certain range; not too much or too little. The eyes want sufficient light to stimulate the light receptors but not too much. When there is low light our pupils open wider to allow more light to enter. When the light increases the pupils close down smaller. This regulates the amount of light entering the eye.
In the video, the pin hole stops most of the light from entering the eye. The pupil opens up to allow the same amount of light to again hit the receptors. BUT, the pin hole also narrows the light that enters the eye into nearly parallel rays compared to without the pinhole. Because the light rays are near parallel, the eyes don’t need corrective lenses to see the image clearly. The image is still not exactly focused, BUT it is close enough that our minds accept the image as good enough to say it is in focus.
***
A camera works the same way. Only it adds two more variables, the speed of the receptor (film or CCD) and the speed of the shutter. An eye does not have variability in either. But the camera wants an exact amount of light to hit the receptor to record the image. Usually, the receptor speed (film speed) is set and seldom changed. That leaves the shutter and aperture to regulate how much light hits the receptor. The two must be balanced out to allow the specific amount of light so the picture is not over or under exposed.
When the aperture is made larger, then the shutter is open for less time and conversely. The advantage is when a larger aperture is used, the light rays are more diffuse and the image has a shorter focusing range. If a smaller aperture is used then the light rays are more parallel making for a longer focusing range. These two characteristics are balanced to achieve different effects.
Sports photography will generally use a large aperture to allow more light to enter in a short period of time. Portrait will also use a larger aperture to limit the amount of the picture in focus. Landscape photography generally uses smaller apertures to keep the entire picture in focus.
I hope this helps. Keep in mind, books have been written on this and I’ve tried to condense it to a few paragraphs.
Wow! That’s quite a dissertation for a guy named “Mr. Catshit.”
#13, Hopper,
My friends call me Bull. I’m convinced it’s because of my size.
Hey Catshit–that actually helps alot and better than anything I could find with google. I don’t think your concept of “parallel” light beams is accurate as the phenomenon arises from the rectilinear properties of light passing thru a pin hole. True, the light rays are NOT diffuse (ie, going off in every direction thereby needing a lens to focus) they are instead sorted by the pin hole into “single rays” from infront of the pin hole, to behind the pin hole.
But, once again, thanks for your valuable input.