Huygens Question - Using a Pinhole Box in the Giant Pinhole Irvine

[ndvcxk123]

TL;DR Summary

The Irvine Giant Pinhole Box generated a ~40m landscape image w. a 4mm hole. Q. is on effects of directing another small pinhole box at the lightsource, while standing in lower part of scenery.

The image generated by the Giant Irvine pinhole cam is a landscape, with features in top of image and ground/water image on the bottom. Now, directing a small shoebox-type pinhole cam at the lightsource while standing only in the lower part of the image (no bldg. features visible there or projected against the user), what does the mini-screen of shoebox-pinhole show ? 1) The ground features only, not the upper part of the giant image, bec. those light portions do not reach the box, or 2) (Huygens?) - a small version of the entire image, including the bldg.detail features in the upper portion ? Thx.

(Ref.)
https://www.worldrecordacademy.org/...-world-record-set-in-irvine-california-422354

 

[Charles Link]

With a pinhole camera, you get a geometric image=light travels in straight lines, (from the source, through the pinhole, and on to the screen).
Diffraction effects with a very small aperture can make for some blurring, but if the pinhole is too large, you also get reduced resolution, because of blurring determined by a point source making a finite sized spot from geometric optics when the aperture is finite. In general, there is an optimal aperture size, where diffraction effects are minimal, and where the spot size from a point source using geometric optics (i.e. using the straight line principle=the aperture shows up on the screen, etc. using ray tracing ) is also reasonably minute.

 

[Charles Link]

To add to the above, you do want to have the pinhole large enough that sufficient light gets through to generate the image, but not so large that the resolution is considerably reduced by having point sources whose image becomes a somewhat large circular spot. Ideally you want the image from a point source to be a very small circle=nearly a point.

Note that the energy that gets through the pinhole to create the image is proportional to the area of the pinhole.

 

[tech99]

If I understand the question, you stand inside the large camera holding a small pinhole camera. In this case, from geometrical considerations, you will form a tiny image of the portion of the scene seen through the 4mm hole, and it will be little bigger than the pin hole. And in addition, the resolution will be softened in the ordinary way by the finite diameter of the hole and by diffraction created by the aperture. The brightness will be very low and I am not certain that anything would be visible.

 

[hutchphd]

You will form a small small dim image of the spot and whatever may be in the line of sight of the spot in the harbor. It will not be useful.

 

[Charles Link]

On this one, I answered it with the assumption that the OP did not know how a pinhole camera works. If he had known the principles of its operation, he would most likely be able to answer any puzzles about it, like the ones he came up with.

 

[ndvcxk123]

If I understand the question, you stand inside the large camera holding a small pinhole camera. In this case, from geometrical considerations, you will form a tiny image of the portion of the scene seen through the 4mm hole, and it will be little bigger than the pin hole. And in addition, the resolution will be softened in the ordinary way by the finite diameter of the hole and by diffraction created by the aperture. The brightness will be very low and I am not certain that anything would be visible.

Thx for responding, the 4mm hole is the entry hole of the pinhole Irvine...as non-physicist reading Huygens, am realizing it was not formulated clearly enough. We are not looking though the 4mm hole, we're looking at the screen of a shoebox pinhole we are holding. I take it your answer is the "portion view" (1) ground. Here diagram:

You will form a small small dim image of the spot and whatever may be in the line of sight of the spot in the harbor. It will not be useful.

Thx for responding. So you are saying also, "only the lower portion." As non-physicist I posted this bec. of Huygens notion of an opening in a barrier replicating an entire wave newly. My view was also (1).

 

[tech99]

Thx for responding, the 4mm hole is the entry hole of the pinhole Irvine...as non-physicist reading Huygens, am realizing it was not formulated clearly enough. We are not looking though the 4mm hole, we're looking at the screen of a shoebox pinhole we are holding. I take it your answer is the "portion view" (1) ground. Here diagram:View attachment 329688

Thx for responding. So you are saying also, "only the lower portion." As non-physicist I posted this bec. of Huygens notion of an opening in a barrier replicating an entire wave newly. My view was also (1).

If the little camera is pointed at the screen then it can form an inverted image of the screen. The cutoff of the image will depend only on the dimensions of the box. The image will be very dim, probably not possible to see anything.

 

[hutchphd]

So you are saying also, "only the lower portion.

I don't think so. I'm saying "only one tiny spot"

 

[ndvcxk123]

If the little camera is pointed at the screen then it can form an inverted image of the screen. The cutoff of the image will depend only on the dimensions of the box. The image will be very dim, probably not possible to see anything.

Hey thx, no, we are pointing the shoebox (its tiny opening) at the source (4mm, far away) not at the screen...

 

[ndvcxk123]

I don't think so. I'm saying "only one tiny spot"

Ok, thx, so with strong magnification, would the tiny spot be a replica of the whole image, or only of lower portion ? (I realize the luminosity is quite low).

 

[hutchphd]

No it will not
The small camera will give thie same image it would give without the "big" camera except that the big camera occludes all but a tiny 4mm spot. You will see only a tinier spot (and what little lies geometrically behind because the depth of field is infinitely deep)
Why don't you build two cameras? Take you half an hour, two boxes and some aluminum foil

 

[Charles Link]

The physics principles of the pinhole camera are rather simple. The light travels in straight lines. For the most part you can ignore diffraction (Huygens) effects. It isn't completely clear to me in how it is stated above if you are pointing the smaller camera at the illuminated city scene or at what is basically the back side of the front face of the larger camera, where all that is illuminated is then just a 4 mm aperture. In any case, if you understand how the light travels in straight lines with these pinhole cameras, (no bending/focusing of the light rays that you get with a lens), you should be able to answer most of what you are asking.

 

[ndvcxk123]

No it will not
The small camera will give thie same image it would give without the "big" camera except that the big camera occludes all but a tiny 4mm spot. You will see only a tinier spot (and what little lies geometrically behind because the depth of field is infinitely deep)
Why don't you build two cameras? Take you half an hour, two boxes and some aluminum foil

My diagram was weak, here it is with the observer, sorry, + thx. You said " would give without the "big" camera except that the big camera occludes all but a tiny 4mm spot. " (Endquote) - So, observer is inside the "Irvine cam" (building) - we are not comparing the two, separately, but one inside the other, w. the observer at the screen side of the small-shoebox pinhole. One barely even sees the 4mm pinhole of the room, and the image they created may have been developed over a longer exposure (I don't know). But assuming similar screen composition/chemicals in the mini shoebox, very weak light is still entering it, though I believe it would just be of the ground scenery, not the top. BTW, I built a shoebox-size pinhole box, + was shocked at the clarity of the image.

 

[ndvcxk123]

The physics principles of the pinhole camera are rather simple. The light travels in straight lines. For the most part you can ignore diffraction (Huygens) effects. It isn't completely clear to me in how it is stated above if you are pointing the smaller camera at the illuminated city scene or at what is basically the back side of the front face of the larger camera, where all that is illuminated is then just a 4 mm aperture. In any case, if you understand how the light travels in straight lines with these pinhole cameras, (no bending/focusing of the light rays that you get with a lens), you should be able to answer most of what you are asking.

Thx so much for sticking w. the topic. For clarity below the observer can now be seen in the diagram.

Re straight lines, was "hoping" for a "wavelet" effect where the light at the bottom somehow still has all the info + creates new wave triggered by the aperture :) :). Thx!

 

[hutchphd]

But assuming similar screen composition/chemicals in the mini shoebox, very weak light is still entering it, though I believe it would just be of the ground scenery,

You may believe what you like even if incorrect. I think my description is clear and I know it is accurate.
The Camera Obscura (trans. room darkened) has a long history in science and art much of it done with a pinhole objective lens.

 

[ndvcxk123]

Hey I'm asking, you guys know the answer if the diagram is clear ?

 

[hutchphd]

I think so. Was my explanation unclear?

 

[ndvcxk123]

No but it referred to another case, so in this case, you are saying the observer gets just a tiny dot on the shoebox screen, the second pinhole has no image creation effect, right ?

 

[hutchphd]

Which is the "second" pinhole?
The big pinhole has no effect on the box image other than to block (almost) all of it. (The holes in this example are large enough that any diffraction effects can be ignored)

 

[pbuk]

No but it referred to another case, so in this case, you are saying the observer gets just a tiny dot on the shoebox screen, the second pinhole has no image creation effect, right ?

No pinhole has any "image creation effect", all the pinhole does is block light from most of the outside world from reaching the screen. If you draw a straight line from a point on the screen through the pinhole you will see where in the outside world that light has come from.

For your smaller camera, you need to draw a straight line through both pinholes to work out what light gets to what part of the screen (if any).

Also note

1. Your labels "city scenery" and "ground scenery" are the wrong way round: pinhole camera images are upside-down.
2. The word "focussed" is incorrect here, pinhole cameras do not focus anything.

 

[pbuk]

The image generated by the Giant Irvine pinhole cam is a landscape, with features in top of image and ground/water image on the bottom.

No, the image generated by a pinhole camera is inverted. The image now displayed in the warehouse is hung the other way up from the way it was created.

 

[Charles Link]

To the OP: You are looking for some kind of magic to occur with two pinholes, and it just doesn't happen. If the hole is small enough in the second pinhole, you can get diffraction effects=especially if you have a bright source like the sun in the line of sight of the two pinholes. Then you could get a ring pattern (the light is not monochromatic though), but you could then get an airy disc type diffraction pattern, instead of a small bright spot on the image screen of the smaller camera. (The smaller the hole, the wider the ring pattern). In any case, you will not magically get the image of the whole scene to appear. The light needs to go through the two pinholes, and neglecting diffraction effects, it travels in straight lines.

See https://en.wikipedia.org/wiki/Airy_disk

Note that if the second pinhole is small enough, you can get the central spot of the airy disc pattern on the image screen to be larger than the bright spot that normally would appear from the 4 mm aperture being observed on the image screen of the second camera. This bright spot can also be larger in size than the spot you would get if you opened up the front face of the first pinhole camera, allowing for direct viewing of the sun with the second camera. It is a diffraction type bright spot, where the light spreads out from interference effects as it emerges from the aperture of the smaller pinhole camera. It in general does not generate an optical image, but is better described as a blurring type of effect=instead of getting the expected small bright spot from geometric optics, (with a small source) when using a very small pinhole for the second camera, the observed spot can be larger than what would be expected from the source and can contain a couple of rings.

 

[sophiecentaur]

If the little camera is pointed at the screen then it can form an inverted image of the screen.

That sounds right. If you (your eye) can see the image on the screen then so will the small pinhole camera. Of course, that second image will be very faint, having only the light through the first pinhole available.

Diffraction will occur at the first pinhole and at the second pinhole. The already blurred first image on the screen will be further blurred by the second pinhole.

One more point: the angular size of a component of the second image will be the same as for the first image, which will be the same as objects in the original scene. Straight lines and similar triangles all along. So images on the second screen will be smaller than images on the first screen.

 

[sophiecentaur]

Which is the "second" pinhole?
The big pinhole has no effect on the box image other than to block (almost) all of it. (The holes in this example are large enough that any diffraction effects can be ignored)

I'd like to add to this. The width of the pinhole affects the resolution of the image - a perfectly thin line in the scene will turn up as a line of roughly the thickness of the pinhole. So bigger gives more blurred due to simple ray optics. BUT smaller will increase diffraction effects. There is a trade-off. This link discusses it with examples.
Note: the optimum size for resolution is inconveniently small when exposure time is involved. Some blur is built in for most practical photography.

 

[Charles Link]

It might be of interest to the OP that the brightness level on the screen of a pinhole camera is on the order of one millionth of the brightness of the scene that is being viewed. Thereby the light levels from observing the first large image with a second pinhole camera would be extremely low.

 

[sophiecentaur]

a second pinhole camera would be extremely low

Definitely. If the small box is 200mm deep and the pinhole size is 2mm, the f number (aperture) would be f100. That's way below the minimum stop of any camera I know of. Think of the exposure time needed.

 

[ndvcxk123]

No pinhole has any "image creation effect", all the pinhole does is block light from most of the outside world from reaching the screen. If you draw a straight line from a point on the screen through the pinhole you will see where in the outside world that light has come from.

For your smaller camera, you need to draw a straight line through both pinholes to work out what light gets to what part of the screen (if any).

Also note

1. Your labels "city scenery" and "ground scenery" are the wrong way round: pinhole camera images are upside-down.
2. The word "focused" is incorrect here, pinhole cameras do not focus anything.

Thx for the corrections. Amazingly, looking through my own pinhole shoebox ab. a month ago, I did not remember it being inverted. (Hence the diag. error). Re focusing, it is interesting though, that it become less sharp if the aperture is widened (due to addit. light entry).

 

[ndvcxk123]

To the OP: You are looking for some kind of magic to occur with two pinholes, and it just doesn't happen. If the hole is small enough in the second pinhole, you can get diffraction effects=especially if you have a bright source like the sun in the line of sight of the two pinholes. Then you could get a ring pattern (the light is not monochromatic though), but you could then get an airy disc type diffraction pattern, instead of a small bright spot on the image screen of the smaller camera. (The smaller the hole, the wider the ring pattern). In any case, you will not magically get the image of the whole scene to appear. The light needs to go through the two pinholes, and neglecting diffraction effects, it travels in straight lines.

See https://en.wikipedia.org/wiki/Airy_disk

Note that if the second pinhole is small enough, you can get the central spot of the airy disc pattern on the image screen to be larger than the bright spot that normally would appear from the 4 mm aperture being observed on the image screen of the second camera. This bright spot can also be larger in size than the spot you would get if you opened up the front face of the first pinhole camera, allowing for direct viewing of the sun with the second camera. It is a diffraction type bright spot, where the light spreads out from interference effects as it emerges from the aperture of the smaller pinhole camera. It in general does not generate an optical image, but is better described as a blurring type of effect=instead of getting the expected small bright spot from geometric optics, (with a small source) when using a very small pinhole for the second camera, the observed spot can be larger than what would be expected from the source and can contain a couple of rings.

Yep, was looking for a Huygen's magic :). Follow on question: Would there be a way of analyzing the contents of the bright dot ? (Are we really only seeing info from the straight line descending to us?) :) :)

 

[Charles Link]

Yep, was looking for a Huygen's magic :). Follow on question: Would there be a way of analyzing the contents of the bright dot ? (Are we really only seeing info from the straight line descending to us?) :) :)

I'm going to try to give you a good answer here, that you might find of some interest. With a single pinhole, one of the better things you can do is use it to observe the sun during a solar eclipse. The first time I observed a solar eclipse with a pinhole camera=seeing the image on the screen with part of the sun obstructed by the moon, I was perhaps ten years old with a very limited science background, and it seemed like magic.

There doesn't seem to be much to gain by using a second pinhole=you can get an airy disc if the hole is small enough, but what could be much more interesting is to replace the second pinhole with two slits, as in Young's famous two slit experiment, or even have multiple slits or a diffraction grating, even of the reflective kind, and the light source (e.g. the sun) will get sorted into the colors of the rainbow, where interference maxima occur when $m \lambda=d \sin{\theta}$, where $m$ is an integer=the condition for constructive interference between adjacent slits or lines (reflective bars) of the grating. With multiple slits or lines the interference (primary) maxima become narrower (in angular spread) as the number (of slits) increases, so that many slits or lines as a grating has (a typical diffraction grating used in spectroscopy can have thousands of equally spaced lines) can sort out the colors in a very dramatic fashion.
(Note: If you use a monochromatic source, the primary maximum (for each integer $m$, usually limited to a couple or a few integers) can then be a very narrow bright spot at a specific angle (with a very small angular spread), and results in what is then called a spectral line).

 

[sophiecentaur]

Thx for the corrections. Amazingly, looking through my own pinhole shoebox ab. a month ago, I did not remember it being inverted. (Hence the diag. error). Re focusing, it is interesting though, that it become less sharp if the aperture is widened (due to addit. light entry).View attachment 329844

There's a problem with that diagram. It appears that the small camera is actually looking at the front of the big camera, which has just a small bright spot in it. The brightness of that spot corresponds to the brightness of the scene in that direction.
We (or at least some of us) may have been talking at cross purposes. What was the actual question - in the light of that possible mis-understanding?

 

[hutchphd]

The fundamental misunderstanding in this thread is manifest in the title. The Huyghens construction (and in fact any diffractive effect) has essentially nothing to do with this analysis because of the sizes involved. Strictly Ray optics... one needs only a ruler and notion of aperture area. All else is irrelevant.

 

[sophiecentaur]

The fundamental misunderstanding in this thread is manifest in the title. The Huyghens construction (and in fact any diffractive effect) has essentially nothing to do with this analysis because of the sizes involved. Strictly Ray optics... one needs only a ruler and notion of aperture area. All else is irrelevant.

Lensless imaging is a hot topic in some quarters of google searches. This link and this link would suggest that the optimum pinhole size includes consideration of diffraction as well as ray geometry. For 200mm deep camera the optimum pinhole size is about 0.5mm so, although an impractical design (far too dim images) it's worth thinking about and not completely irrelevant.

 

[hutchphd]

For the situation described I will respectfully disagree.
One of the hallmarks of the art piece described is its mammoth size.
Using your numbers for the small camera the pinhole angular resolution limit ~.5/200=1/ 400 but the diffraction limit for 500nm (bluegreen ) light will be ~500nm/0.5mm=1/1000 so it would not be high on the list. (Honestly it is bigger than I had anticipated!!)

 

[Charles Link]

Lensless imaging is a hot topic in some quarters of google searches. This link and this link would suggest that the optimum pinhole size includes consideration of diffraction as well as ray geometry. For 200mm deep camera the optimum pinhole size is about 0.5mm so, although an impractical design (far too dim images) it's worth thinking about and not completely irrelevant.

I would agree. The OP seems to be on a learning curve when it comes to optics and pinhole cameras, (as well as diffraction theory), but we should not discourage him from getting what he can out of what should be a good learning experience.

Edit: To comment on post 34, which I just saw=the OP should soon figure out if he hasn't already, that there is little to gain by using a pinhole camera on the image of another pinhole camera. In any case, he picked a good topic, and we ought to be able to at least point out a couple of things of interest for him.