Optical instruments, such as cameras, microscopes, and telescopes, are used to produce images for viewing or detection. Most use several individual lenses in combination to improve performance. You’ll learn how to analyze a system with multiple lenses.

《 LOOKING BACK Sections 34.5–34.6 Thin lenses

A camera uses a lens—made of several individual lenses—to project a real image onto a light-sensitive detector. The detector in a digital camera uses millions of tiny pixels.

• You’ll learn about focusing and zoom.

• You’ll also learn how to calculate a lens’s f-number, which, along with shutter speed, determines the exposure.

  

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The human eye is much like a camera; the cornea and lens together focus a real image onto the retina. You’ll learn about two defects of vision—myopia (nearsightedness) and hyperopia (farsightedness)—and how they can be corrected with eyeglasses.

Lenses and mirrors can be used to magnify objects both near and far.

• A simple magnifying glass has a low magnification of $2\times$ or $3\times$.

• Microscopes use two sets of lenses to reach magnifications up to $1000\times$.

• Telescopes magnify distant objects.

  

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Color depends on the wavelength of light.

• The index of refraction is slightly wavelength dependent, so different wavelengths refract at different angles. This is the main reason we have rainbows.

• Many materials absorb or scatter some wavelengths more than others.

  

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Light passing through a lens undergoes diffraction, just like light passing through a circular hole. Images are not perfect points but are tiny diffraction patterns, and this limits how well two nearby objects can be resolved. You’ll learn about Rayleigh’s criterion for the resolution of two images.

《 LOOKING BACK Section 33.6 Circular-aperture diffraction