On optics, light, etc ..... wow this photography thing is getting deep!

snapsnap1973 · Jan 3, 2015

Ok, this morning I'm really getting interested in the "origins of photography" and was reading about the camera obscura. I guess this goes back to BC Aristotle, etc. Anyways, I got to the part about light going through the hole and crossing opposite directions and of course "flipping" the image and now I'm curious about the whole field of optics I guess!

Darn, now I've gotta go read up on optics! Sir Issac Newton anyone?? LOL.

Anyways, before I go read I though I'd ask a simple (yeah right!) question about how light works. Ok so of course we have to have a light source in order to percieve objects correct? So I'm guessing that light travels from say the sun to an object and then "bounces off" that object to our eye (the sensor) and we percieve it?

Before I go off to read about "optics" and without having really read up on optics, how am I doing so far in my understanding??

Also, I thought that I read that "light travels in straight lines" somewhere today. So if light is bouncing off an image of something and traveling in a straight line, how does it "bend" to enter the tiny hole in the wall if it's not in a direct line with that hole?

I mean say your camera obscura is pointed towards a landscape and there's a mountain that goes up higher than the tiny hole you have in the wall. Does the light bend to get through from the height of the mountain?

This is fun!! Here I go off to read!

480sparky · Jan 3, 2015

At least you didn't pick a boring hobby.

JustJazzie · Jan 3, 2015

I'm sure the experts will chime in here, but think about a pool table. If the ball is hit, it doesn't usually (unless hit straight on) go in a straight line from there, it bounces off at an angle. When it hits the Side of the table it never bounces where it came from, but in an opposite direction. The motion is still linear, but it can Change direction.

Hopefully that made a bit of sense. I'm precaffinated, so my brain only half works. ;-)

Designer · Jan 3, 2015

In higher theory, light may actually bend, but here on earth we just consider straight lines only. The reason an entire mountain can go through a tiny hole is because the rays at the top (going in a straight line, remember) go through the hole and strike the wall at the bottom. Similarly, the light rays coming from the bottom of the mountain go through the hole and strike the wall near the top.

Simple, really. And since light has no mass (except in higher theory) ALL the light rays can squeeze through a very tiny hole all at the same time, without rubbing shoulders or stepping on the feet of their companions.

snapsnap1973 · Jan 3, 2015

Thank heavens for Issac Newton!

480sparky · Jan 3, 2015

Get a copy of Light, Science and Magic.

dennybeall · Jan 3, 2015

You hit the nail on the head with the straight line concept. The light from the extreme left of the scene comes thru the hole and since it's in a straight line it goes to the far side of the film plane, The light from the right side goes in a straight line which takes it to the left side. It's a big "X" with the pinhole at the crossing point. Hence the light on the film plane is a reversed image........

soufiej · Jan 3, 2015

Designer said:
In higher theory, light may actually bend, but here on earth we just consider straight lines only. The reason an entire mountain can go through a tiny hole is because the rays at the top (going in a straight line, remember) go through the hole and strike the wall at the bottom. Similarly, the light rays coming from the bottom of the mountain go through the hole and strike the wall near the top.

Simple, really. And since light has no mass (except in higher theory) ALL the light rays can squeeze through a very tiny hole all at the same time, without rubbing shoulders or stepping on the feet of their companions.

Ask a physicist, "What is light?" If they don't begin with, "Well, see ... ", you know to ignore their response. The enigma of "light" as we presently understand its operation suggests it can be either a wave or a particle. As a wave, you are correct, it has no mass. As a particle, it has mass.

I would say the op has somewhat mistaken the operating principles of the human eye with the functional properties of a camera's lens. However, to the basic question ...

"Also, I thought that I read that 'light travels in straight lines' somewhere today. So if light is bouncing off an image of something and traveling in a straight line, how does it 'bend' to enter the tiny hole in the wall if it's not in a direct line with that hole?

I mean say your camera obscura is pointed towards a landscape and there's a mountain that goes up higher than the tiny hole you have in the wall. Does the light bend to get through from the height of the mountain?"

Your question would possibly be vaild IF only one particle or wave of light were to strike and bounce off that mountain. Of course, life in general would be very different should there only be one particle (or wavelength) of light bouncing around the universe. The "straight line" concept is useful for certain experiments and discussions. It is not, though, how life actually exists. Essentially, what this means to the photographer is more like, if the mountain is in front of your lens, you aren't going to see the tree on the far side of the mountain.

Here the operation of the human eye is far more useful and should be considered the analog to the aperture setting of your camera's lens. The answer provided by saying, " ALL the light rays can squeeze through a very tiny hole all at the same time, without rubbing shoulders or stepping on the feet of their companions", is the best answer. The mountain does not represent one single particle of light but rather an innumerable number of particles which the aperture allows us to focus on. Think of the lens as the starting point of the "image" you wish to capture and the objects in front of the lens determined or "confined" to an angle defined by the focal length of the lens. The op's question would appear to be thinking of the mountain as the starting point for the image, which, for the purposes of this question, it is not. Not for the purpose of focal length at least. The important word is "ALL" of the light (particles) enter the lens since there will be a very large number of (straight line) waves which arrive at the plane of the lens.

Squint or otherwise change the aperture of your eye or your lens and your depth of field will change accordingly. One difference between the human eye (and the human mind which makes sense of the incoming electrical signals) and the aperture of the lens would be, the lens has what we call a depth of field not completely shared by the eye. The "hyper-focal" length of the lens is not the same as the focal abilities of the human eye. Basically, the human mind is what "sees" the images and it has the ability to perceive an image into an almost infinite distance. Being a mechanical device, a camera lens lacks the cognitive abilities of the human eye and only accepts what it is told to accept.

By altering the aperture of the lens, we can intentionally alter the depth of field of the lens system which will cause several of those particles to literally "rub shoulders with" others. This results in a less sharply focused image across certain planes, changing in specific and predictable ways. In other words, if you were to create a small hole in a piece of cardboard and look through the hole at the mountain, your eye's mechanisms (and your mind's capacities) would de-focus on the cardboard directly in front of your eye and would instead focus on the mountain on the opposite side of the hole. A lens, however, is a bit more limited in its ability to discriminate between such objects which it defines as a series of planes extending from the lens itself and outward to the object we wish to capture as an image. The lens would tend to focus on the cardboard and would not clearly recognize the image on the opposite side.

soufiej · Jan 4, 2015

After reading yesterday's response this AM I think it might help the op to think about light from the viewpoint of the lens/sensor, not from the viewpoint of the mountain. Obviously, the shutter cannot move at a speed faster than that of light. Therefore, what the sensor "sees" (ignoring the fact the sensor in a digital camera only sees a series of 1's and 0's which define an on-off status as fed to each pixel by the image processing system) would be a series of planes running parallel to the lens/sensor itself. Think of a series of slices of this "pie shaped wedge", near infinite in number, with each slice containing the reflected light bouncing from the subject under examination. It is the classic example of focal length which shows the angle of view beginning at the lens and extending forward from the lens to the subject; http://media.digitalcameraworld.com..._is_hyperfocal_distance.dof_take_further3.jpg All the op needs to do with that example is to add an infinite number of slices to the viewing angle making each slice run parallel to the plane of the lens/sensor/film.

Within each slice is the image of the subject represented by reflected light coming from the subject. Focal length and aperture define the angle of view and the hyperfocal distance. The hyperfocal distance defines which aspects of the reflected light will be captured without interference by other light waves/particles thus creating a sharply defined image. Those same factors will also determine which waves/particles will create the interference which throws the image out of focus.

The light wave does not need to bend in this example. It is either within or outside of the viewing angle of the lens in each slice. It is also either passing through the lens without distortion or it is being distorted by the lens' focal length and aperture.

"When you focus on an individual point within your landscape, you are in fact creating a plane of focus that lies parallel to the sensor"; Getting Landscapes Sharp: Hyperfocal Distances and Aperture Selection - Digital Photography School

Make sense?

photoguy99 · Jan 4, 2015

You need to know about almost none of this stuff to take pictures. It's great that you're enjoying yourself, but it's no more related to photography than petroleum chemistry is to driving a race car

480sparky · Jan 4, 2015

But there's nothing wrong with learning the technical side of the craft either.

Designer · Jan 4, 2015

photoguy99 said:
You need to know about almost none of this stuff to take pictures. It's great that you're enjoying yourself, but it's no more related to photography than petroleum chemistry is to driving a race car

You can denigrate the OP for asking the question, but me, I am happy to attempt to answer it.

sashbar · Jan 4, 2015

The particles of light exhibit the qualities of a particle and simultaneously of a wave. That is true for any elementary particle by the way, and is known as wave-particle duality. To understand what light is and why it behaves this way you can read quantum theory. It is really a kids stuff and you will crack it in no time. Niels Bohr and Heisenberg wrote about the metaphysical nature of the duality paradox, start with digging those guys. It will not take long, I am sure it will take you no more that 4-5 days. Did I say days? No no, it is years, not days. 4-5 years. Then come back and start shooting and posting your images there. I am sure the light in your images will be wonderful.