1. Basic Optical Devices
Part 2
Lenses

2. Lenses
Lenses are curved pieces of glass, plastic or crystal. There are two types of lenses:
Diverging which have at least one Concave side:
Have a virtual Focus
Always create a smaller virtual image that is closer than the object…
So they are used to correct nearsightedness
Are used in telescopes as only as a part of a compound lens

3. Converging which have at least one Convex side:
Used to gather light & into a real focus,
Creates an erect virtual and larger image
of an object placed closer than its focus
the image is farther away than the object
so they are used to correct farsightedness
Create inverted real image
Of an object placed farther away than the focus
That get smaller the farther away the object is
Converging lenses are often used in telescopes
projectors, cameras etc.

4. Prisms
Prisms are flat sided pieces of glass, plastic or crystal, They are used to:
disperse white light into a spectrum.
change the direction of a ray of light
Diffraction Gratings
Diffraction Gratings are a series of parallel slits usually in a plastic film.
They use diffraction to disperse white light into a spectrum
A Spectroscope is a devise that uses a prism or diffraction grating to study spectra