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A Simple Explanation On How Aperture Impacts Depth Of Field (And Why Pinholes Are Always Sharp)

by 5 Comments

lenses-pinholes

There is a Seinfeld episode where George loses his glasses, yet he is able to spot a coin on the floor by squinting. Without knowing the team at Seinfeld made a very elegant scientific experiment comparing lenses to pin holes.

A Lens makes things sharp by focusing rays of light coming from a source so the rays converge on a single sport.

A pinhole, on the other hand, only allows light to enter from a single direction thus not letting it blur.

Both aspects are very clearly explained in this video by MinutePhysics.

Indecently, this video also explains how aperture works and why the Bokeh Masters Kit makes star shaped bokeh.

So why most applications prefer a lens over a pinhole (which is obliviously cheaper to manufacture?) Because pinholes work by blocking light the resulting image is significantly darker.

[How to See Without Glasses via reddit]

Related posts:

What Actually Happens When You Stop Down a Lens Don’t Have a Polarizer? This Tutorial Just Might Convince You to Get One Everything You Need To Know About Depth of Focus and Lens Equivalency What the heck is hyperfocal distance?

  • You seriously need to rethink this sentence: “Because pinholes work by blocking light the resulting image is significantly darker.”
    Really? That’s exactly what a mechanical iris does. Compensate for a smaller aperture by using a longer exposure time, whether it’s a pinhole or a precise diaphragm.

    • yup! a “stopped down” mechanical iris is just like a small pinhole. On that section though, I am comparing pinholes optics to lens optics.

      • Nope. It doesn’t matter what you’re comparing it to. Exposure is exposure. A pinhole does not make an image darker. Underexposure makers an image darker.

        • Tom Meyer

          it does reduce the light, but as we all know, you’ll just need to extend the exposure time to collect the same amount of light as a wider aperture, since the stuff actually accumulates, like all matter (electrons, ya know?).
          If you’ve ever tried focusing a big view camera with a small maximum aperture lens (like f11 or smaller), you’ll understand what I think Udi means when he says it’s darker… it’s like looking into a cave as compared to that 85mm 1.2 on your Nikon/Canon.

          My (different) observation about this post is that while pin holes (and smaller apertures in general) *do* increase depth of field, making more stuff *in focus*, that doesn’t mean they are “sharper”. It just means more of the scene is in focus.

          Sharpness is a function of lens optics and construction. Depth of field (what’s “in focus”) is a function of aperture size. Another thing about small apertures is that in extreme cases, they actually degrade the sharpness, an aberration known as diffraction.

  • catlett

    Pinholes are not always sharp. It depends on what is capturing the image. e.g. try a pinhole on a D800 and you will be very disappointed with the sharpness because of refraction issues.

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