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

[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.

 

[hutchphd]

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

I can only speak to what I am trying to do: no points, imagined or otherwise, are involved. What you do is up to you. Please do not presume to speak for me.
The concept of a giant camera obscura has much pedagogical merit. I am interested because the diffraction scale is fixed by the wavelength of the light so that the diffraction limited angular acuity of a large camera scales with size. That pedagogy was being totally lost on the OP.