What size pinhole

How big should I make the pinhole?

D. Browne

The size of the pinhole controls the quality of the image you see.

  • The bigger the hole, the brighter the image is.
  • The bigger the hole, the more blurred the image is.
Blurring by a big pinhole

In a pinhole camera, light from one place on the sun’s surface does not end up at one point on the screen. Instead, it ends up spread over an area on the screen the same size as the pinhole. So, two points close to each other on the sun end up with overlapping spots on the screen, making the image blurred.

The amount of blurring depends on the width of the pinhole, and the distance from the pinhole to the screen.

If the width of the pinhole is about 1/1000-th of the distance to the screen, the sun is 10% blurred.  Sharp features on the sun (like the moon’s edge or a sunspot) are smeared over about 10% of the sun’s diameter.

If the width of the pinhole is bigger than 1/100-th of the distance from the pinhole to the screen, the sun’s image is completely blurred.

So, we should have very tiny pinholes if we want sharp images.  Those are faint images, of course.   It also turns our there is another problem.

Blurring from Diffraction

Light doesn’t actually travel in perfectly straight lines, like rays. Since light is a wave, light that passes through as small opening, like a pinhole, will actually spread out as it passes through. All waves do this. Water waves on the ocean will appear to ‘bend around’ a sea wall. It’s called diffraction.

The smaller the hole, the worse the spreading out from diffraction becomes.   A pinhole that is too small results in a faint and very blurred image.  So, there is a minimum hole size where the diffraction starts to make the blurring worse.   Here is a table

Distance to screen  Minimum pinhole diameter
 Minimum blurring
2 ft 0.04″ 18%
5 ft 0.06″ 12%
10 ft 0.09″ 8%
20 ft 1/8″ 6%
50 ft 3/16″ 5%

If your hole is close to the optimum size above, you will be fine.

How do I make small holes?

Here are some common objects and the size of the hole they make

  • 0.7mm mechanical pencil lead = 0.03″
  • Jumbo paper clip = 0.04″
  • #2 pencil lead = 0.1″
  • Outside of a #2 pencil= 0.25″

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