Imaging instrumentation

Imaging Instrumentation

Basic Properties of Instruments

  • Imaging instruments are tools used to visualise or capture images of objects and areas.
  • They function based on various principles such as reflection, refraction, polarisation, and interference of light.
  • Types of imaging instrumentation include the human eye, cameras, microscopes, telescopes and other optical devices.

The Human Eye

  • The human eye works much like a camera.
  • It has a lens that focuses light onto the retina, which serves as a light-sensitive screen.
  • The lens changes shape to focus light from objects at different distances, a process known as accommodation.
  • The blind spot is the point on the retina where the optic nerve exits; it has no light-sensitive cells and therefore we cannot see light that hits it.
  • Colour perception is based on three types of light-sensitive cells that respond to different parts of the spectrum.

Camera

  • A camera captures images by focusing light onto a light-sensitive surface, like a film in traditional cameras or a sensor in digital cameras.
  • It uses a lens to focus light, and the aperture controls the amount of light allowed in.
  • The shutter speed determines how long the light-sensitive surface is exposed to light.
  • A camera’s depth of field refers to the distance between the closest and farthest objects that are in sharp focus in an image.

Microscopes and Telescopes

  • Microscopes magnify small objects to enable detailed observation. They have a compound design, with two sets of lenses for magnification: the objective and the eyepiece.
  • Telescopes gather light from distant objects and focus it to create an image. They use either lenses (refracting telescopes) or mirrors (reflecting telescopes).
  • The Focal length of a telescope is the distance between the lens or mirror and the point where the object is brought into focus.

Interferometry and Polarimetry

  • Interferometry uses the principle of interference to measure distances or examine the detailed structure of an object.
  • An interferometer splits a beam of light into two, reflects them back, and then recombines them to create an interference pattern.
  • Polarimetry is the science of measuring the polarisation of light.
  • Instruments such as polarimeters and spectropolarimeters are used to measure properties of light including its polarisation angle and ellipticity.

Medical Imaging Devices

  • X-ray machines use short wavelength electromagnetic waves to create images of dense substances like bone inside the body.
  • Ultrasound scanners use high-frequency sound waves to produce images of organs and structures inside the body.
  • Magnetic Resonance Imaging (MRI) leverages the property of nuclear magnetic resonance to visualise internal structures.

Lenses in Optics

  • Converging or convex lenses gather light and bring it to a point. They are thicker in the middle than at the edges.
  • Diverging or concave lenses scatter light away from a point. They are thinner in the middle than at the edges.
  • The focal point or the focus of a lens is the point where light rays meet or appear to diverge from.
  • Lens aberrations refer to distortions in the image resulting from the lens design. There are two main types: chromatic and spherical aberration.