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

[sophiecentaur]

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.

But getting the picture the right way round is pretty important. What is he trying to image with the small camera? Is it an image of a pinhole or an image of the large camera image? This is not a mere detail imo.

 

[Charles Link]

But getting the picture the right way round is pretty important. What is he trying to image with the small camera? Is it an image of a pinhole or an image of the large camera image? This is not a mere detail imo.

Or even the scene with the first camera absent. From what I can gather, he seems to want to try all 3 cases, and see if there is something of interest for each.

 

[pbuk]

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.

This was covered in #2:

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.

From the article linked in #1:

A seamless piece of muslin cloth was made light sensitive by coating it with 21 US gallons (80 l) of gelatin silver halide emulsion and then hung from the ceiling at a distance of about 80 feet (24 m) from a pinhole, just under 6 millimeters (0.24 in) in diameter

From the aperture size calculator linked in #33:

Focal length of camera in millimeters 24000
Optimal pinhole size: 5.7... mm

But none of this affects the key point that the image you get can be simply determined by ray tracing (it just means that the image is blurred due to (1) rays from opposing extremes of the aperture hitting the screen at different points and (2) individual rays forming diffraction patterns. The smaller you make the aperture the better you make (1) but the worse you make (2) as well as image brightness (increasing exposure time), and vice versa.

 

[sophiecentaur]

The smaller you make the aperture the better you make (1) but the worse you make (2) as well as image brightness (increasing exposure time), and vice versa.

That point was already made and there are links quoted with some actual figures.
As for diffraction limiting image quality, that's clear because astrophotography (and observing) requires apertures as big as your can afford.

 

[sophiecentaur]

For the situation described I will respectfully disagree.

After thinking more about the OP, I have to agree that the whole scheme has very modest requirements for resolution. My comments were basically about squeezing the last juice from the imaging lemon so we can ignore diffraction in this project. in fact, the 'pinhole' should to be as big as possible, consistent with the acuity of the viewers and their distance from the screen - i.e the old 'five times picture height' rule for viewing distance with standard definition TV would set the size of hole for best picture brightness / sharpness tradeoff. The Irvine 4mm (?) camera hole may have got it fairly right. But this appears to have been more of a 'record breaking stunt'. The resolution would not have been very special, with brightness the more important for impressiveness.

 

[ndvcxk123]

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.

Well, I wondered whether sampling with a small opening might recreate the full wave entering...

 

[ndvcxk123]

But getting the picture the right way round is pretty important. What is he trying to image with the small camera? Is it an image of a pinhole or an image of the large camera image? This is not a mere detail imo.

Well, was not sure what the result would be....

 

[sophiecentaur]

Well, I wondered whether sampling with a small aperture might recreate the full wave entering...

You would need to explain that more fully. I have made assumptions:

There is a tradeoff between aperture and resolving power. The smaller the aperture, the wider the diffraction pattern. Assuming you could describe the resultant wave from light entering from all across a scene then a tiny aperture would not allow discrimination between light from all the different elements of the scene. So you'd just get a (slightly weighted) value at one emerging angle from your small aperture which is a sum of light flux from all different directions.
The nearest thing to the "full wave entering" would be obtained with a massive aperture.

 

[ndvcxk123]

But getting the picture the right way round is pretty important. What is he trying to image with the small camera? Is it an image of a pinhole or an image of the large camera image? This is not a mere detail imo.

Re learning curve: After constructing first pinhole shoebox cam, find that it works, but I'm running out of breathing air quickly closing black coat around it + my head ! :) The other aspect interesting me is image reflection w. out a lens, bec. still, from the middle of the image there are just slightly diagonal lines which should cover the other middle objects. However, pinhole images, while weak, are still really precise. To me, that's surprising.

 

[hutchphd]

Pinhole cameras are a lot of fun and useful teaching tools, but are really quite simple. Here is how they work:

Light from the object travels in straight line through the hole to the image.

That's all you need to know 99.9% of the time

 

[sophiecentaur]

However, pinhole images, while weak

"Weak"? In terms of galactic distances, the James Webb Space Telescope is a pinhole. You can hardly say that's weak when it gets us back to the formation of the Universe.
JWST does need some very long exposures to get there, though.

 

[ndvcxk123]

Pinhole cameras are a lot of fun and useful teaching tools, but are really quite simple. Here is how they work:

Light from the object travels in straight line through the hole to the image.

That's all you need to know 99.9% of the time

 

[ndvcxk123]

Pinhole cameras are a lot of fun and useful teaching tools, but are really quite simple. Here is how they work:

Light from the object travels in straight line through the hole to the image.

That's all you need to know 99.9% of the time

"The straight line" you mention is part of the standard description. But (sorry), it seems to me to be inadequate, or too symbolic. Consider the roof tiles, tow. center. Take one of the tiles. The space next to it is another tile. Would you not accept that light from the first, at equal intensity, also covers the left and right tile ? Should we not say that cones (small though they are) enter the aperture ? Too me, it seems that each source object throws a cone of light larger than the pinhole, i.e. each feature reflection covers the pinhole completely +causes entry of a pinhole-sized cone.. (I realize this contradicts noninterference on the screen)
Thx.

 

[hutchphd]

The space next to it is another tile. Would you not accept that light from the first, at equal intensity, also covers the left and right tile

No I would not.
Please show me how that works. If you just mean that the pinhole has some finite size then that will provide blur. The light (ignoring diffraction) will travel in a straight line. The angular effect of diffrraction ~lambda/d where d is the diameeeter of the pinhole (so very tiny for the giant camera).

 

[sophiecentaur]

Too me, it seems that each source object throws a cone of light larger than the pinhole

Light from parts of the object that are close to the hole will form a 'cone' with a bigger angle than parts in the background. But, if you actually do the sums, the angles are all 'small' in a working pinhole camera. If not, then use a smaller pinhole or only look at distant objects.
BUT it's only the cone of light that actually gets through the pinhole. The rest is cut off.

 

[ndvcxk123]

No I would not.
Please show me how that works. If you just mean that the pinhole has some finite size then that will provide blur. The light (ignoring diffraction) will travel in a straight line. The angular effect of diffrraction ~lambda/d where d is the diameeeter of the pinhole (so very tiny for the giant camera).

 

[hutchphd]

Yes?

 

[ndvcxk123]

Note the small white dots at the tip of the arrow within the projected image of the Irvine pinhole, (diameter 6mm). Multiple, superthin lasers can project rectilinearly straight through the hole. For convenience, assume that the white paint dots of interest are precisely centered. Now, moving the laser a nanometer would still allow moving the projection point a bit, (just a bit, else one is outside of the pinhole). So now, the case of diffuse light: These little dots, like millons of other source, fill the pinhole completely, I would have thought they would start to cover each other, spreading ? Yet they are clearly defined. Why is there not more "coning"? Thx.

 

[ndvcxk123]

(Its not allowing posting of the image, sorry...)

 

[hutchphd]

Why is there not more "coning"? Thx.

"The straight line" you mention is part of the standard description. But (sorry), it seems to me to be inadequate, or too symbolic. Consider the roof tiles, tow. center. Take one of the tiles.

Because the "'standard description" is, in fact, completely adequate despite your misgivings. Shall I repeat it, only louder ...or less symbolically somehow?.
The sources are considered points and hundreds of meters away across the harbor so the amount of ''coning" can be easilly shown to be very very small (make a scale drawing using straight lines). This means that the angular size of the image matches that of the object.

 

[berkeman]

(Its not allowing posting of the image, sorry...)

Use the "Attach files" link below the Edit window to upload a JPEG or PDF file.

 

[sophiecentaur]

No pinhole has any "image creation effect", all the pinhole does is block light from most of the outside world from reaching the screen.

That is a very sweeping statement. If you acknowledge that a convex lens has an "image creation effect" then the same has to be said about a pinhole. A lens with an extremely small aperture is effectively a plane sheet of glass because the angles for all light paths from object element to image are more or less the same.

 

[hutchphd]

That is a very sweeping statement.

Indeed that seems a bit overstated. An image is to my reckoning any continuous one to one (usually) optical mapping. A pinhole lens does not provide any focus is probably a better way to put it.

 

[sophiecentaur]

A pinhole lens does not provide any focus is probably a better way to put it.

A form of aberration, along with all the others. But definitely nothing special, except that the simplest ray optics will show how a pinhole works (at a basic level). I am hoping that the OP is now able to do that simple (and universal) ray optics for a range of optical imaging arrangements.

 

[pbuk]

If you acknowledge that a convex lens has an "image creation effect"

Yes, a convex lens creates an image of an object (which is at a distance >> 2f) just beyond its focal plane.

then the same has to be said about a pinhole.

No it doesn't. Where would that image be?

A lens with an extremely small aperture is effectively a plane sheet of glass because the angles for all light paths from object element to image are more or less the same.

This is not correct. A lens with a focal length of 35 mm has a focal length of 35 mm no matter how small its aperture. Edit: With a tiny aperture it is only possible to get a tiny image, With any aperture the further you move the screen (or film) away from the lens the more out of focus the image becomes. With a plane sheet of glass (or none at all) this does not happen: because there is no focus it cannot become "less focussed", as you move the screen away from the pinhole the image gets larger and stays just as "blurry" with the amount of "blurryness" dependent only on the aperture.

 

[sophiecentaur]

With a tiny aperture it is only possible to get a tiny image,

Not at all. When you alter the aperture of your camera, do you only get a selected bit of the original image? * The only 'restriction' of image size is the depth of the hole / dimensions of the lens etc, which will actually cut off the direct light path. Draw a scale diagram of a 4mm hole in a piece of 1mm foil and see the possible range of angles of a straight line through the hole. Use 0.5mm foil and the angle opens up still further.

You need to try to see what's actually going on here and not to stick to your preconceived mental model. PF is not wrong in this matter.

*cheap lenses can exhibit 'vignetting' around the edges of an image so they can claim to have a larger aperture than is justified. Avoid!!

 

[pbuk]

An image is to my reckoning any continuous one to one (usually) optical mapping.

If you like (although for a perfectly focussed image isn't it a many to one mapping?). And a pinhole does not create any optical mapping, all it does is destroy mappings.

 

[pbuk]

A pinhole lens does not provide any focus is probably a better way to put it.

Yes that is a good way to put it, however you are taking my comment out of context. The OP wrote:

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 ?

...implying that the first pinhole was creating some "magic" which the second pinhole was not. So I wrote

No pinhole has any "image creation effect", all the pinhole does is block light from most of the outside world from reaching the screen.

In the same post I also wrote

1. The word "focussed" is incorrect here, pinhole cameras do not focus anything.

What are we trying to do here, split hairs and score points off each other or correct fundamental misconceptions?

 

[sophiecentaur]

If you like (although for a perfectly focussed image isn't it a many to one mapping?). And a pinhole does not create any optical mapping, all it does is destroy mappings.

Sorry but that is nonsense. There is no method of 100% accurate mapping of a scene onto a plane image. Quality is on a scale from really bad to quite good. A lens has many ways of messing up that mapping; it's referred to as Aberrations. You name it and your £nk lens has it at some level.
A 'perfectly focussed' image will be as near to one to one mapping as the lens can manage.

In fact the only reason to use a bigger aperture than a pinhole for most imaging is the small amount of light it lets through. Diffraction is the last thing on a normal photographer's mind - but astrophotography is another problem and it's 'least worst' that counts here.

 

[pbuk]

Not at all. When you alter the aperture of your camera, do you only get a selected bit of the original image? *

No, of course, this was nonsense and I have corrected it.

 

[vanhees71]

Sorry but that is nonsense. There is no method of 100% accurate mapping of a scene onto a plane image. Quality is on a scale from really bad to quite good. A lens has many ways of messing up that mapping; it's referred to as Aberrations. You name it and your £nk lens has it at some level.
A 'perfectly focussed' image will be as near to one to one mapping as the lens can manage.

In fact the only reason to use a bigger aperture than a pinhole for most imaging is the small amount of light it lets through. Diffraction is the last thing on a normal photographer's mind - but astrophotography is another problem and it's 'least worst' that counts here.

One should add that you can easily check for yourselfe that a pin hole creates an image:

https://blackcreek.ca/how-to-make-your-own-camera-obscura/

 

[pbuk]

One should add that you can easily check for yourselfe that a pin hole creates an image:

https://blackcreek.ca/how-to-make-your-own-camera-obscura/

This thread started with a working example and the 64 subsequent posts have (mostly) tried to correct misconceptions about that working example. I am not sure another working example is going to help the OP with their misconceptions

 

[pbuk]

Perhaps it is time for a summary, corrections and improvements gratefully received:

• The larger the aperture of (any) camera the more light it lets in and so the brighter the image is.
• The further away from the pinhole the screen is the larger the image is.
• The light in a pinhole camera travels in straight lines: there is no focussing.
• Because of this pinhole camera images are blurred and in general the blurring of the image is directly proportional to the diameter of the aperture and the distance to the screen.
• We can make the image sharper by decreasing the size of the pinhole, but eventually it will be small enough that diffraction effects become important, although in general the image will become too dim to view before diffraction effects become significant.
• If we are using film with a long exposure time to record a (static) image we should calculate the optimum size of aperture where the blurring due to aperture size and diffraction effects are similar. Using the Fraunhoffer approximation for a circular diffraction pattern we get the diameter $d \approx \sqrt{2.44f\lambda}$ https://en.wikipedia.org/wiki/Pinhole_camera#Selection_of_pinhole_size.

 

[vanhees71]

This thread started with a working example and the 64 subsequent posts have (mostly) tried to correct misconceptions about that working example. I am not sure another working example is going to help the OP with their misconceptions

Well, if you have somebody not believing what's told about the phenomena, the best thing you can do is to let him observe these phenomena himself. Then you can try to explain it in terms of theory.

 

[sophiecentaur]

Because of this pinhole camera images are blurred and in general the blurring of the image is directly proportional to the diameter of the aperture and the distance to the screen.

This is true but, if you take a bog standard lens, you find that the other aberrations - spherical / chromatic etc. are at least as bad. So much so that, for good depth of field (landscapes with foreground) you stop down as far as possible to remove the 'lens-ness' of the camera. Fact is that pinhole blur is minimal in most cases.