The primary function of a telescope is to magnify distant objects, making them appear closer and larger than they actually are.

Reflecting telescopes use a concave mirror as their primary objective to collect and focus light from distant objects.

The eyepiece of a telescope magnifies the image formed by the objective, allowing the observer to see a magnified view of the object being observed.

A microscope is an optical instrument used to magnify small objects, allowing the observer to see details that are not visible to the naked eye.

A compound microscope uses the principle of refraction of light to magnify small objects. The objective lens refracts light from the object, forming an enlarged real image. The eyepiece then refracts light from this real image, forming a further enlarged virtual image.

A spectroscope is an optical instrument used to analyze the composition of light by separating it into its component wavelengths.

A prism in a spectroscope disperses light into its component wavelengths, allowing the observer to analyze the composition of the light.

A periscope is an optical instrument used to view objects that are hidden from direct view, such as objects above or below the observer's line of sight.

A periscope uses the principle of reflection of light to allow the observer to view objects that are hidden from direct view. Light from the object is reflected by a series of mirrors inside the periscope, allowing the observer to see the object.

A goniometer is an optical instrument used to measure the angle of incidence of light on a surface.

A collimator in an optical instrument produces a parallel beam of light, which is used to illuminate the object being observed.

A refractometer is an optical instrument used to measure the refractive index of a material.

A refractometer uses the principle of refraction of light to measure the refractive index of a material. The refractive index is determined by measuring the angle of refraction of light passing through the material.

A focal length meter is an optical instrument used to measure the focal length of a lens.

A focal length meter uses the principle of refraction of light to measure the focal length of a lens. The focal length is determined by measuring the distance between the lens and the image formed by the lens.