How It Works?

aaronmichael · May 23, 2011

I was telling some of my friends about pinhole photography the other day, showing them my plastic 35mm film canister pinhole cameras and some photos I took with them. They all asked the question "Well how does that work?" I told them that all the light from outside the pinhole travels towards the pinhole and then spreads back out after passing through the pinhole, therefore creating the image. Then one of them said "But how does that work?" and I was at a loss for words - haha. So is there a more complicated science behind it or is it really as simple as what I told my friends? That's the only way I knew how to explain it. How have you explained pinhole photography to people that didn't know about it?

bobwysiwyg · May 23, 2011

This is pretty straight forward. The only thing I might add is the light doesn't 'spread' so much as the light point will appear 'opposite' positionally within the camera. At least that's my explanation.

http://www.howstuffworks.com/question131.htm

Poisson Du Jour · May 23, 2011

The method of pinhole cameras goes back a long, long way to the very basic origins of image formation "caught in the box".

The simplest "how it works" explanation is that light rays from the scene pass through the single (pinhole) point and project an inverted image on the opposite side of the box (onto film, or any photosensitive material enclosed).
Our eyes, in bright light act in a similar way, as do modern cameras using quite small apertures. Pinholes don't have a mirror to flip the image right-way up, like the human brain does, or by which SLRs using mirror systems accomplish the same thing.

In this month's National Geographic magazine is a fascinating spread on pinhole photography using a large format set up to project images onto walls in homes, on the ground in floorless tents and a demonstration of the simplest visual explanation of image formation using a light globe to visibly project an inverted image of it inside an open (no photosensitive material) cardboard box pinhole "camera". It's well worth a look for the innovative twist on an old method.

Ric Johnson · May 25, 2011

I tell people that pinhole cameras/photography acts the same as any other photograph. The only difference is pinhole cameras do not have a lens, which means the photograph has a softer effect.

puptent · May 25, 2011

bobwysiwyg said:
This is pretty straight forward. The only thing I might add is the light doesn't 'spread' so much as the light point will appear 'opposite' positionally within the camera. At least that's my explanation.

http://www.howstuffworks.com/question131.htm

Originally known as Camera Obscura. A room, or tent, with a pinhole aperture that projects an image on the backwall or an easel for tracing by an artist or draftsman inside a darkened room. The diameter of the pin hole is related to the focal length, or distance between the pinhole and the capturing surface; the wall, a piece of film, photo paper, whatever. If the diameter of the aperture is too large, like a window, there will not be the inversion and focusing of the image. I think that theoretically, there is an optimum focal length for each pinhloe aperture that will focus perfectly, or am I wrong about that? So, in theory, if the focal length was long enough wouldn't an aperture as large as a window focus an image?

puptent · May 25, 2011

Oh, and BTW, the mirror in an SLR serves only to re-direct the light from the lens to the eyepiece, it swings away just before the shutter is opened, and the image captured on the film will be whatever is fucused by the lens. And it's true that the image on the back of your eye is inverted, all babies see everything upside down until the brain learns how to compensate.

bobwysiwyg · May 25, 2011

all babies see everything upside down until the brain learns how to compensate.

How do 'they' know that?

puptent · May 25, 2011

Hi wysiwig (love the handle!) the cornea is a lens, and it has physical properties the same as a lens, so, what's on the back of your eyeball is the inverted image of what ever you are looking at. Your brain actually learns how to rotate the image so that it makes sense. =)

aaronmichael · May 25, 2011

I'm aware of the focal length, diameter of pinhole, apertures,...etc. I was just having a hard time trying to explain it and how it works. I suppose it is as simple as a beam of light passing through the hole and ending up projected on the other side. I think I'll have to use the flashlight example next time I try to explain.

bobwysiwyg · May 25, 2011

What I really meant, but didn't phrase correctly is, how do they know the baby doesn't see it the same way we do right from the start? Did they ask them?

MattKing · May 25, 2011

bobwysiwyg said:
What I really meant, but didn't phrase correctly is, how do they know the baby doesn't see it the same way we do right from the start? Did they ask them?

I have a long time friend who, as part of her pre and post doctoral work did some fascinating research on questions concerning how babies perceive and learn. The tests that she and others came up to check on many commonly held hypotheses were/are really creative. Asking babies directly doesn't work, but sometimes there are ways of getting them to tell you what you want to know .

tim k · May 25, 2011

Its magic.

aaronmichael · May 26, 2011

tim k said:
Its magic.

Sure is when you stand inside of a camera obscura for the first time.

Chirs Gregory · May 26, 2011

"Water, fire, air and dirt,
Pinhole cameras, how do they work?"

Same way magnets work: Miracles.

That is precisely how I would have answered the question. Of course, I would have followed up with "But really, the light from an object passes through the aperture, getting inverted along the way, until it hits the paper or film and produces an image." I mean, defining focal length, f-stop and diffraction and all that jazz is fun, but most of the time people are either wondering about why you're standing there with a Quaker Oats tin, or they're trying to tell you that you've left your body cap on.

puptent · May 26, 2011

Hmmm, so maybe we can't ask babies what they see... but they do give them acuity tests right after birth. Also, there are survivors of head trauma who have had inverted vision for a period of time. And then, it might just be FM (freakin magic) after all.

SMBooth · May 29, 2011

It possibly an explanation why babies are always falling down.....

moki · May 29, 2011

SMBooth said:
It possibly an explanation why babies are always falling down.....

You got it all wrong... adults fall down too. If baby's saw everything inverted, they'd fall up

I always explained pinholes with the fact that light travels in straight lines/rays through air (may be a half-truth, but good enough for most people and easy to prove) and a little sketch of a camera. It's not hard to understand that only the rays of light that form the image are let through and all others are blocked. When it comes to more complicated cameras, "magic" is the more useful explanation, as I could explain it all, but would take days.

IAphotog · Feb 14, 2012

Also, the cornea is not the primary focusing device of the eye. Your eye has a lens just behind the iris, that changes shape to focus at different distances. Pupil is the variable aperture and retina is the receiver of the upside-down, reversed image. Brain makes the corrections necessary for understanding of what our eye perceives.

My $.02

Steve Smith · Feb 14, 2012

puptent said:
Your brain actually learns how to rotate the image so that it makes sense. =)

Or your DNA already knows that the image is upside down and grows your optical nerves with that in mind.

However, if you fit someone With a pair of glasses which reverse the iamge, they will very quickly be seeing things the right way up again.

Steve.

holmburgers · Feb 14, 2012

Imagine you're in a pinhole camera, or better yet, picture a large room that's been made into a camera obscura with 1 small diameter hole in the window looking outside, and a large flat wall opposite that.

Ok, now imagine what you'd see through that hole if you were looking out from various points on the wall. Putting your head near the floor for instance, you'd be looking up through the hole and out onto perhaps the top of a tree, the sky, or the roof of your neighbors house. Now put your head near the ceilling and through the hole you can only see the ground outside, the trunk of a tree, or the sidewalk.

The aperture only lets in a small circle of light from any given direction and this shines on the back wall. Imagine every point on the back wall and knowing that there's a ray of light making a beeline from the outside to the inside... well you can see basically how the image is formed.

And it's true, you could have a 5-foot diameter window and as long as the "film plane" was (perhaps) several hundred feet on the other end, an image would be formed.

pawlowski6132 · Feb 14, 2012

If you remember that light always travels in a straight line, that will help. So, imagine light bouncing off the top of the building. It travels through the pinhole and hits the bottom of the film. That's why, in a ground glass everything is upside down and inverted. It's not really "spread" through the pinhole.

Newt_on_Swings · Feb 14, 2012

pawlowski6132 said:
If you remember that light always travels in a straight line

Not always, it bends a bit around objects with lots of gravitational mass. (insert yo momma joke) jk lol

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