Inside the Camera Obscura

You can either imagine yourself very small, or the camera obscura very large. Whatever suits you.

You are standing with your back against the wall, and looking through the opening in front of you.

There are two distinct images we have to consider.

1) The retinal image of the outside scene, which will be of course inverted, allowing you to see the outside scene the normal way.

2) The image projected through the opening on the wall against which you are standing. This image will be much larger than your eyes, and probably overflow all around you. That is an image you only can see if you change position and face the wall.

The question now is: will making the opening smaller make both images darker, or only the second one?

You should know my answer by now.

he light coming through the opening seems to brighten all the closeby space, and the more light there is, the wider the bright space becomes. — Hachem

We've been through this... Space cannot be "bright". If you're referring to the light reflected from particles floating around in space, this is something different. It's been long proven that you cannot see photons without having them enter our eyes or else through some form of "detector" (i.e: something for them to strike)

That would be the only reason for projected images to become darker by smaller aperture — Hachem

The reason why smaller apertures result in less bright images is because fewer photons (electromagnetic light waves) make it through the aperture and strike the array of sensors. The lens redirects the incoming light waves onto the array, so if more light is coming in then more will be focused onto the photo-sensitive array, resulting in a brighter image. On a polaroid style camera the image becomes brighter because more photons strike the light sensitive coating on the photo, causing cumulative chemical reactions to create brighter and darker spots.

At the same time, that is only possible if the images are not directly projected by light rays, since otherwise they should keep the same brightness as long as the same scene is projected. — Hachem

Since diffuse light expands outward in all directions (and gets weaker as it does so) light from an object should not magically retain some "brightness" component when viewed from different distances. Brightness has more to do with "how many waves of light are available for detection" and "how sensitive is the detector (i.e: what is the minimum number of light waves required for it to register a unit of "brightness", and what is the maximum number of light waves it can detect in a given time period before it registers "maximum brightness".)

We wear sunglasses because they reflect a great deal of light which makes objects appear less bright.

How can that be under your presumptive regime?

Camera sensors react to light first, to color second. Or maybe the other way around. It does not matter. — Hachem

Do you have any sweet clue how different kinds of cameras actually work?

If not, what makes you so confident that anything you say about them is accurate?

Did you know how "color" is determined? If I explain it to you, will you listen?

The eye cells also react this way. A white beam directed into the eye can give different color impressions, and different cells can give the same visual impression, whatever their first inclination. — Hachem

A "white" beam is "white" because it appears "white". I don't know what you're trying to say here though; it's incoherent. What do you mean "their first inclination"? Which eye cells exactly?

It seems you accept that cellular biology is real, but how can you trust data from traditional/electron microscopes if you cannot see cells with your eyeball by getting really close to them?

There is no reason to believe that increased sensitivity has to come at the cost of sharpness, and the latter becomes anyway irrelevant the darker it is. — Hachem

Generally sensitivity comes at the cost of sharpness because it's very hard to fit more sensitive light detectors next to to each-other in an array. You can use the same array to produce an image that is more sensitive, but you will have fewer pixels in the end because instead of a single photo-receptor being used for a single pixel, groups of adjacent photo-receptors all waiting to detect light will all be used together to produce a more "sensitive" photo-receptor for a single pixel (thereby reducing the number of overall pixels).

It is known that the eye cells need to be refreshed, and that happens through constant eye movements. When projecting an image directly on the retina, and having the image follow the eye movements so that the same cells are perceiving constantly the same image, the image disappears from perception. My interpretation of this fact is that we are simply in presence of overexposure, and not some mysterious neural program that would stop the eye cells from functioning if the image does not chan — Hachem

I am having a hard time deciphering what you mean. Which eye cells?

What do you mean by "the image follow the eye movements so that the same cells are percieving constantly the same image, the image disappears from perception"? The way that eye movements contribute to "eye cell" refreshing is by changing the light that is activating given "eye cells" which gives them a movement to regenerate their light sensing capability. Blinking achieves the same effect. If you stare at a light bulb and look away or close your eyes you can still see an "image" of the light bulb which "follows your eye movements" because the "eye cells" there are taking longer to regenerate than their surrounding "eye cells".

This all means according to me that in fact ambient light is contributing only indirectly to image formation. Larger apertures, or longer exposure, would apparently make the wall or the screen in the camera obscura, the film or the sensor chips, more sensitive, up to a certain limit. — Hachem

"Ambient light" is just diffuse light from some external source or "the light that is already present in a scene". Bigger photo-sensitive arrays, longer exposure times, larger apertures, all means more light data can be collected, which means more detail and contrast can be put into the images we can create

If you look at some of the pictures carefully, you will see some dark shadows where light did not enter even after months of exposure. — Hachem

I don't actually see evidence of this, although the idea is that where less light strikes the photo-sensitive film there is less chemical reaction, so there should be some darker spots....

1) When beams of light travel through space, they leave their bright traces behind them. — Hachem

No, long exposure times show that light leaves traces when photo-receptors detect them

2) Ambient light is only additive up to an extent. Non-moving objects which are not in shadow nor in the path of light beams, keep most of their details even after hours, days, or months of exposure. (I find this puzzling) — Hachem

Define ambient light.

Objects like a tree will keep their details because they move very little, and so over time the few photons per minute which actually strike the film take the same shape. When something is moving though, you get blurred streaks as the moving object throws light from different directions (which strikes the film at different places).

3) There remain places from which bright scenes can be observed, which themselves remain cloaked in shadow. — Hachem

You haven't even mentioned anything pertaining to this mechanic in this post; you're just throwing it on at the end as if you have demonstrated it. Please explain the error with the following info-graphic:



If you can see the stars on a moonless night, then you are bathed in starlight (not darkness). If you are under a tree on a starry but moonless night, then you are bathed in the ambient light being reflected from the surrounding objects that are being struck by starlight. If you are locked inside of a box with no internal light source, then you are not visible unless you have something special like a thermal camera. Since all objects above zero kelvin do emit some EM waves (thermal radiation) you would need to be in a box and at zero kelvin in order to be in a true absence of light... I could dig out the other info-graphic but you get the idea...

The question now is: will making the opening smaller make both images darker, or only the second one? — Hachem

Fewer photons will be entering the camera to be spread out over a given area, so generally, yes..

It's been long proven that you cannot see photons without having them enter our eyes or else through some form of "detector" (i.e: something for them to strike) — VagabondSpectre

I find this a very strange assertion in this context. We are talking about visible light, like for instance a beam of light directed towards or away from us. We can see this beam of light if the medium allows it.
As for instance in a swimming pool where the water is not "pure".

I have no trouble with the idea of invisible photons that only detectors could see. But we are talking about enough photons to create an image on our retina. Wherever we stand. Still you persist in your affirmation that they will remain invisible and that the area where we stand will remain utterly dark.

What if we you were to spray some chalk dust around you? Would the chalk dust become visible?

I would consider that as an empirical test for my analysis: if the dust become visible, then somehow photons are reaching the dark place of the observer.

I can tell you that It is very improbable. You will be able to make the (laser) beam visible, but not the photons leaving the beam and impinging on your retina.

Of course, if you think that even the dust would remain invisible, then I wouldn't know anymore what to tell you.

I find this a very strange assertion in this context. We are talking about visible light, like for instance a beam of light directed towards or away from us. We can see this beam of light if the medium allows it.
As for instance in a swimming pool where the water is not "pure". — Hachem

The "medium" (like fog or something?) reflects the "beam" in many directions ("diffuses it"). Some of that light enters our eyes, allowing us to perceive some of the light from the beam. If it didn't enter our eyes we would not see anything. If there was nothing in the medium to reflect the "beam" (ie: vacuum, empty space), then we would not see it. This is an experiment you can try out for yourself.

I notice that all you are doing is reciting the Optics gospel. You are not answering my question which could put an end to this sterile discussion.

I am offering an empirical test, all you do is repeat what is in the textbooks.

I notice that all you are doing is reciting the Optics gospel. You are not answering my question which could put an end to this sterile discussion. — Hachem

I notice that you have failed to address any of my objections yet again by labeling me as religious. you should be aware that this is nothing more than a puerile attempt to avoid the blatant problems with your ideas.

The beam pointed away from you is invisible unless something is there to reflect it. If enough light gets reflected from a beam maybe adequate light would be available to see the white powder you sprinkle about your person.

You cannot see the beam: do this test yourself; it's a test which has been performed many times. If you have a laser pointer you can do the test yourself.

I have done the test, and I have seen it done on Youtube. I will give you the link as soon as I find it back.

"gospel" in this context has no religious connotation.

I do not feel like repeating our long and boring discussion where you stick to the official theory and I have to defend myself.

I thought we could avoid it by trying to be as objective as possible and devising empirical tests like the one I proposed, and of which you deny that it is even possible.

I do not feel like repeating our long and boring discussion where you stick to the official theory and I have to defend myself — Hachem

Prove to me that the beam is visible then. Show me the youtube video. Personally, I do not feel like repeating our long and boring discussion where you don't defend yourself.

Let us be clear on the test, and I will keep searching.

1) The subject shines a beam of light away from him at another object (in this case a lens).
2) He blows a handful of chalk dust in the air to make the beam visible.
3) the beam becomes visible, but no dust linking the beam to the subject is visible.

Agreed?

Let us be clear on the test, and I will keep searching.

1) The subject shines a beam of light away from it at another object * in this case a lens).
2) He blows a handful of chalk dust in the air to make the beam visible.
3) the beam becomes visible, but no dust linking the beam to the subject is visible.

Agreed? — Hachem

I asked you to prove that lasers pointed away from us are visible without something to reflect them.

This experiment demonstrates nothing as ive already explained: the diffused light coming from the chalk particles within the laser beam probably wont reflect sufficient light to make chalk particles outside the beam visible.

Let us give up the pretension that we could ever agree on even the simplest of tests.

Let us give up the pretension that we could ever agree on even the simplest of tests. — Hachem

How about you respond directly to the dialogues you keep initiating on this forum?

I asked you to prove that lasers pointed away from us are visible without something to reflect them. Please do so.

Because I already did, while you refuse systematically to discuss my empirical objections.

You prefer, like everybody until now, the safe discussion where your are exposing the "scientific" theory while pushing me in the weirdos' corner.

I will pass and not answer until you decide to take my objections seriously, not in a general way, since we have already done that.

Why don't you comment on my pictures concerning double slit, newton rings and interference? That would be very precise and empirical. Your chance to show that I just don't get it.

Why don't you comment on my pictures concerning double slit, newton rings and interference? That would be very precise and empirical. Your chance to show that I just don't get it. — Hachem

Your slit "experiment" wasn't controlled or well described and defined to any reasonable degree of precision, nor were your interpretations of the results clear, nor were your conclusions warranted. Half of what you write borders incoherence.

"Light doesn't travel in waves because I don't understand this interference pattern" isn't scientific, precise, or empirical, therefore i cannot address it as such.

Why do you claim that laser beams are themselves visible?

what are you afraid of?

Why do you claim that laser beams are themselves visible? — VagabondSpectre

not me no how

stop trying to hit me and hit me!

https://youtu.be/FVpPU4NIJh0
around 1:55 mn. You can see the beam, but no link to the subject.

But then, that was because the photons are invisible and too few, right?

edit: no link to the camera either that is filming all this.

what are you afraid of? — Hachem

I'm afraid that after taking the time to read and respond (by trying to explain simple proven science to you) you will just bail on the conversation by saying "you're appealing to the gospel of accepted science" or something like it and open a new and equally challenged thread.

stop trying to hit me and hit me! — Hachem

This isn't how debates work. Your confused view of light stems from faulty presumptions like "like beams are visible" or "a particle of dust in between me and an illuminated particle of dust should be visible".

I'm just about the only one bothering to make any responses to your threads, so if you want to get anything out of them other then you need to address the content of my objections.

When you say "why isn't the particle between me and the illuminated beam visible?" and i respond " because the light reflected off a few particles isn't bright enough to then detect by looking at another particle with the naked eye", then it's your turn to respond and actually address the current point of contention

around 1:55 mn. You can see the beam, but no link to the subject.

But then, that was because the photons are invisible and too few, right? — Hachem

and at 2:07-2:09 you can see the cloud of talcum powder reflecting the normal ambient light when he blows it.

What do you mean "link" to the subject? ("link" left undefined makes your point here incoherent). Why would there be a "link"? The talcum powder reflects light in random directions, not just toward observers.

why are you procrastinating?

I am sure I could formulate my ideas better, more precisely, more carefully.

I am also certain that I am far from knowing everything there is to know about physics, or even about Optics.

But I am presenting you with empirical claims. The wet dream of every scientist, and you keep babbling about generalities?

and at 2:07-2:09 you can see the cloud of talcum powder reflecting the normal ambient light when he blows it. — VagabondSpectre

But we see the beam not only from that place, but from anywhere!

But I am presenting you with empirical claims. The wet dream of every scientist — Hachem

The wet dream of every scientist is an intuitive theory with empirical evidence to back it up.

Please provide evidence that shows we can see collimated beams of light in a vacuum...

Please provide evidence that shows we can see collimated beams of light in a vacuum... — VagabondSpectre

You are really pathetic in your avoidance strategy. Please do not waste my time anymore.

But if I leave you alone you won't get any responses...

Your strained writing skills and inability to clearly explain anything stop half of your would be respondents, and the sheer ridiculousness of your ideas stops the other half. I'm either stupid or very patient for even making the effort to respond.

Presently you want me to address your claim that there should be a visible "link" between a laser beam and a camera it points away from. What do you mean? Like a shaft of light? No, because dust diffracts and reflects light in many directions, not just toward the camera (therefore we should see a field of light, not random or single shafts emanating from the main laser) and because light reflecting off dust particles get partially absorbed, which weakens it, and because as diffuse light expands outward in many directions it becomes less intense.

A laser beam in fog will have a slight glow around the beam but it's not going to visibly illuminate the entire sky due to atmospheric diffraction and reflection; the light isn't strong enough to do so...

If you think that a visible shaft of light should appear between a laser beam and a camera it is pointing away from if you blow talcum dust through it, then you evidently still do not understand the scientific description of light.

When we blow talcum powder into a laser, that's why it becomes visible; we are seeing photons which bounce off particles and travel in our direction (but remember it travels in many directions, not just towards our eyes). The ambient light or "diffuse light" created from a laser and some dust isn't always significant though, so while it might appear like you can see the beam itself and are "cloaked in darkness", you're actually not seeing the beam, you're seeing light from it reflected off dust particles, and you're not cloaked in darkness, you're being illuminated (albeit at low or undetectable levels) by the same mechanism which allows you to "see the beam", light reflecting off dust particles.

Look at this picture:

It is a laser pointer being made visible by snow. Do you see the glow which surrounds the laser? This is due to light being reflected off snow. Notice how the beam gets noticeably weaker the further it travels, this is because more and more of it has been diffracted and reflected by snow. The glow is strongest where the beam is strongest (at the beginning) and steadily gets weaker until it becomes undetectable.

There is no missing shaft or link...

I'd rather have no responses that dishonest responses. I never say there should be a link, only that if photons were propagated in all directions, that there should be a reaction of the matter between us and the beam. For instance, chalk dust should light up.

It does not, and your answer is well known enough. No use to repeat it to me. I say it does not light up for the simple reason that there are no photons going our way. What makes us see object is still a puzzle, but the contemporary theory of light does not convince me.

But you already knew that.

Now, if you won't answer to my challenge, and that is, to keep it simple:

How do you explain the pictures I made of a laser beam that look so much like Newton rings, or cases of interference?

Face my empirical queries or give it a rest.

I'd rather have no responses that dishonest responses — Hachem

This kind of unwarranted snobbery is also going to scare people away. You shouldn't say "I'm not educated in physics at all and am hoping to have my errors explained to me", and then when people actually start explaining things say "I'm going to basically ignore and disregard everything you write by labeling it as a dishonest appeal to authority".

It's lazy and transparent. Sophistry at best, gibberish at worst...

Let's carry on!

I never say there should be a link, only that if photons were propagated in all directions, that there should be a reaction of the matter between us and the beam. For instance, chalk dust should light up. — Hachem

why should only the chalk between us and the beam be illuminated? if the room was filled with chalk dust, there would be a glow around the actual laser beam, but it probably wouldn't be strong enough to illuminate the entire room. Did you read my last post? I explained this already...

It does not, and your answer is well known enough — Hachem

My answer is not well known enough?

I still don't know what you're really trying to say with "for instance, chalk dust should light up" because you're so vague and imprecise in describing things. Which chalk should light up? The chalk between us and the laser? Again, why should only the chalk between us and the laser light up?

What makes us see object is still a puzzle, but the contemporary theory of light does not convince me. — Hachem

You don't understand the contemporary theories concerning light.

How do you explain the pictures I made of a laser beam that look so much like Newton rings, or cases of interference?

Face my empirical queries or give it a rest. — Hachem

I don't know because you have so poorly described your "experiment" (just like "why isn't there a link between us and the beam") that nobody has any sweet clue what exactly you're talking about.

In a lab they measure everything with precision and give exact and plentiful instructions for how the experiment is to be duplicated. The most amount of info that I have is that you have a Nikon camera, a pinhole lens, a laser pointer, and have been screwing around with it. I don't even know if the photos you took are actually interference patterns and not some other phenomenon...

Nobody is going to try and debug your poorly executed experiments...

Inside the Camera obscura (2)
The distinction between the retinal image and the projected image can hopefully help us understand why a laser beam directed through a (multiple) slit creates the images we know with bright and dark spots.

Imagine your retina as wide as the screen, and looking at the grating.

However you move your eye, or move through the camera obscura, you will see the beam through at least one slit at a time.

But you won't be able to see it through the gaps between the slits. They will be represented as dark lines or bands, just like the window grating on the upper floor of my building.

The difference between this picture, and the ones taken with a grating, as that of the bookshelf and the outside scene on one hand, and that of the laser beam on the other, is that the latter does not fill the entire width of the visual scene, but only a very circumscribed location.

What we are seeing therefore is each time the same beam, but then through another slit, with spaces in between them.

Only one beam image

Try as I may, I could not, using the grating, get the nice lineup of bright and dark spots when directing the laser beam through a pinhole lens, or even through an open body. Changing the distance and the exposure time did not change a thing, and I thought that I was making a mistake somewhere.

When I held the same slide in my hand and pointed the laser beam through it, I got the same image one sees in all clips and textbooks.

I then realized that the camera sensors did react somewhat like a retina. They took a picture of the laser mouth through the slit directly facing the camera. By shifting the camera slightly to the right or the left, another image of the same laser was taken.

The central image overwhelmed the other parts, and I had to reduce the exposure time drastically to get other, smaller, red points representing what I think was the laser beam. But the points were, as a consequence of the reduced exposure, not very detailed.

I also got sometimes more than one very bright spot, which I think was more a matter of false reflection and bad centering of the beam than anything else.

I am therefore left with the necessity of interpreting unclear images, or rather, relying on the ones usually used in this kind of experiments.

I do not believe in the theory of constructive and destructive interference. I think it is unnecessarily complicating some very simple facts:

Light has to go through splits that are separated by opaque bands, We see bright and dark spots. Why should it surprise us?

The dark spots are only visible under certain circumstances, like my pictures show.

The wider the object or the scene is, the less visible the grating will be,

But in the case of a localized light source, the grating will be prominent, and we will have the pattern that has puzzled every scientific mind since Newton.

Inside the Camera obscura (3)

There remains at least one question unanswered.

How come we get practically the same pattern with one slit?

Here are some preliminary suggestions.

Imagine walking at night along the road on a full moon. The moon seems to be following you. That is of course a simple optical illusion because the distance you can walk at anytime is infinitely smaller than the moon is large, and the distance separating you from it.

What is important is that, each time, you see a complete moon, and it is always as sharp.

If we replaced you with a camera which would be moved only microns at a time, the result would still be the same: one sharp moon for each position.

I do not think you could find a position, however close to the preceding one, that would show you a double or unsharp image.

In other words, wherever you are, you see one moon, and one moon only.

It does not really matter how that happens since that would only bring up an undesirable polemic.

When a grating is used, the opaque bands take care of the dark spots.

But we also know that the grating can be made invisible, as good as absent, without changing the image.

Whether the grating is present or not, different copies of the same object could be projected on the screen, depending on the size of the sensors and other technical properties.

VagabondSpectre, you are wasting your precious time. Hachem isn't interested in the truth, as it is apparently incompatible with what he wants to believe. He has an agenda that he is going to pursue no matter what. Beating your head against this wall is only going to give you a headache. I've encountered this type of person before. You will not make any progress with him. Walk away.