B (Huygens) Irving Giant Pinhole variation: Extend it with a 70 mm tube?

[ndvcxk123]

TL;DR Summary

So my (non-physicists) quest. is on object-expansion vs interobject separation + why light diffusion based on emitting surfaces can be expected to be similar...see example.

For simplicity: The Irv. pinhole image contains some white spots from paint on a parking lot. We are placing the pinhole w. tube directly across. (Micr. AI) said we should now get a smaller image of the spots. Can we agree that: 1) At that distance, diffuse light fr. each spot, fills the tube completely, and 2) yet they are projected w. space in between? and 3) Experimentally increasing/distancing the screen would cause a size expansion, contraction (right?). For simplicity, we repainted the grey (also reflecting) asphalt in a non-reflective black coating, so we just have the two spots. So the separation of the spot, and the spots themselves increase at the same rate (I take it) (Image proportions maintained.)
My q. is does the image size, on pulling screen back, only increase bec. of angular changes of rays, or is there an inherent mechanism of expansion when light is emitted from the aperture ? Thx.

 

[sophiecentaur]

TL;DR Summary: So my (non-physicists) quest. is on object-expansion vs interobject separation + why light diffusion based on emitting surfaces can be expected to be similar...see example.

bec. of angular changes of rays,

There is no angular change between rays as they pass through the pinhole, Any reduction or magnification is due to the relative distances between object and image. In a camera the magnification is less than unity.
Of course, the hole size affects the resolution because of multiple paths through a narrow cone. You would need to explain better what you mean about the "bright spots". If you are getting specular reflections of the Sun from parts of the scene then the apparent size of spots can increase because of the diffraction - same sort of effect as you get with reflecting telescopes and very bright stars which have 'starburst' distortion.

 

[ndvcxk123]

Thx Sophie ! So the white spots are just two spots of white paint from parking guidelines, (3 cm diameter) (don't have the image now). Note that we are discussing a case w.o. a lens, all we did is add a tube (of varying length). Now angular effects (rectilinear beam entering on right, exiting inside on left are minimized, though still there, and increase with distance). Is the projected image totally proportional ? And I take it the aperture itself has zero effect, we see the expanded image only bec. the beams were at diff. angles at the outset. The central, empty non-reflecting space is growing also, so inter-object distance also slowly increases. Can one really say that rays from each spot are filling the tube completely ? How tiny would the image be under those conditions. (The screen of the Irv.G.P. is quite far away fr. the pinhole). Thx!

 

[hutchphd]

What is your intent with the tube?? It will cut down light from the edges but that is not extraordinary. Is there a purpose for doing this? A picture is worth 4000 words.......

 

[sophiecentaur]

Can one really say that rays from each spot are filling the tube completely ?

It depends on how wide the tube is and which actual direction it's pointing. I'm not convinced that you have understood what's going on here. Did you try drawing a diagram and adding those rays you ask about?
Each item in the scene is producing rays in all directions (unless it is a collimator or shiny plane reflector etc). Some rays will enter the pinhole and get to the screen to form a part of the full image. How narrow is this tube of yours``? Is it narrower than the pinhole? Draw it out if you want an answer. It all depends on the actual situation. When it blocks rays, they won't get through (obvs).PS If you have a problem with ray diagrams then Google "Optics ray diagrams" for examples.