Pinhole Projector: How Many Photons, How Small a Hole for Shape?

[mishima]

I'm confusing myself trying to explain the pinhole projector (card with pin point hole used to watch eclipses). How many photons are required, or how small a hole could you maintain, to still get the apparent shape in the projection? Why? Obviously only one photon isn't enough to describe the shape in a projection, and too small a hole would eventually produce diffraction and interference. Any thoughts?

 

[Drakkith]

You are correct. But a pinhole is not small enough to introduce those effects. Or at least not on a scale big enough to cause an issue with general observing on an eclipse.

 

[Andy Resnick]

I'm confusing myself trying to explain the pinhole projector (card with pin point hole used to watch eclipses). How many photons are required, or how small a hole could you maintain, to still get the apparent shape in the projection? Why? Obviously only one photon isn't enough to describe the shape in a projection, and too small a hole would eventually produce diffraction and interference. Any thoughts?

Consider the fact that the object is of finite size- if you like, photons are entering the pinhole from different directions. As long as that directional information is preserved, you will form an image. Pinholes in cards are many wavelengths in diameter- so you can see just fine with a 'pinhole camera'.