Skip to main content
\( \newcommand{\lt}{<} \newcommand{\gt}{>} \newcommand{\amp}{&} \)

Section3Simple Optical Instruments

Subsection3.1Magnifier

Use a convex lens as a magnifying glass. The image you see when looking through the lens is a normal, erect, and virtual image.

<<SVG image is unavailable, or your browser cannot render it>>

Figure3.1Converging lens as a magnifier.

Subsection3.2Refracting Telescope

Hold up a large convex lens, facing a fairly distant window. Move a paper screen until an image of the window appears on the screen. Now use a smaller convex lens as a magnifying glass to examine the back of the screen. Pull the screen out of the way; if you are still looking through the smaller lens, you should now see a magnified image of the window. That is, you are looking through a telescope.

The virtual image seen is both inverted and perverted. The large lens is used to focus (i.e. gather) a large amount of light which is then refined by the smaller lens so that the light can be processed correctly.

Figure3.2Double refraction as in a refracting telescope.

Subsection3.3Reflecting Telescope

Place a concave mirror so that it faces a fairly distant window. Move a paper screen until an image of the window appears on the screen. Now use a convex lens as a magnifying glass to examine the back of the screen. Then remove the screen and you should find yourself looking through a reflecting telescope.

The virtual image seen is both inverted and perverted. The mirror is used to focus a large amount of light which is then refined by the lens so that the light can be processed correctly.

Figure3.3Refraction of reflection as in a reflecting telescope.