Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Pinhole CameraPinhole Camera

Imaging Science Fundamentals

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Typical imaging chain for pinhole cameraTypical imaging chain for pinhole camera

Visible light source

Object

Dark box

pinhole

Film (capture)

processing

Image

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Light from a Point SourceLight from a Point Source

A point source is a source in which the light appears to be emanating from one point in space.

A point source casts energy in all directions, shown above as rays.

A star can be considered a point source. (Why?)

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Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Point Source Casting RaysPoint Source Casting Rays

Take a look at 7 of the rays cast from one position (the tip) of the object.

With no collection element, all of these rays fall on the “image plane.” There is no way to determine the source of the rays.

Object

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Three Points on the ObjectThree Points on the Object

This becomes a problem when three points on the object are considered.

The energy can be collected at the image plane, but all information about the object is lost.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Need for Collection ElementNeed for Collection Element

A crucial element in most imaging systems is the component responsible for collecting the energy emerging from a given point on the object, such that it is brought to a single point in the image.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Ideal Pinhole CameraIdeal Pinhole Camera

An ideal pinhole allows only a single ray from each point on the object to pass through. This preserves the spatial distribution of energy, creating a sharp image.

An ideal pinhole camera has an infinitely small aperture (opening).

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Problems with Ideal Pinhole CameraProblems with Ideal Pinhole Camera

An infinitely small aperture allows an infinitely small amount of light (zero) to pass through.

Diffraction (which is ignored in geometric optics) blurs the image when the pinhole is very small.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Realistic Pinhole CameraRealistic Pinhole Camera

Since the pinhole cannot be infinitely small, more than one ray actually gets through, blurring the image formed at the image plane.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

CaptureCapture

The image can now be captured using a detection system, such as photographic film.

Film must be processed to yield a permanent, visible image.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Image Capture - Photographic FilmImage Capture - Photographic Film

Film consists of a photosensitive compound known as Silver Halide (AgX), which reacts with light.

The area exposed to light turns dark after processing.

The total amount of light hitting a given area of film (known as exposure) determines how dark that area turns.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science

Limitations of Pinhole CameraLimitations of Pinhole Camera

Finite pinhole size and diffraction degrade final image.

Light collection is poor - aperture must be small - so image acquisition is slow.