Question

which are advantages of reflecting telescopes? check all that apply.
there is no rainbow - like halo around the image.
reflecting telescopes can be made very large.
reflecting telescopes use only lenses, not mirrors.
only the reflecting side of the primary mirror needs to be perfectly shaped and smooth.
the eyepiece creates an image for the observer.

Explanation:

• No rainbow - like halo: Reflecting telescopes do not suffer from chromatic aberration (which causes rainbow - like halos in refracting telescopes as different colors of light are focused at different points). Since reflecting telescopes use mirrors (which reflect all wavelengths of light in the same way), there is no such halo.
• Can be made very large: Mirrors in reflecting telescopes can be made larger. In refracting telescopes, large lenses are difficult to make (they can sag under their own weight). Mirrors can be supported from the back, so reflecting telescopes can have larger apertures (which is important for gathering more light and seeing fainter objects).
• Only reflecting side of primary mirror needs to be smooth: For a mirror in a reflecting telescope, only the front (reflecting) surface needs to be perfectly shaped and smooth. In a refracting telescope (which uses lenses), both sides of the lens need to be precisely shaped.
• "Reflecting telescopes use only lenses, not mirrors" is incorrect. Reflecting telescopes use mirrors (e.g., a primary mirror) as the main light - gathering element.
• "The eyepiece creates an image for the observer" is a function of both refracting and reflecting telescopes and is not a unique advantage of reflecting telescopes.

Answer:

• There is no rainbow - like halo around the image.
• Reflecting telescopes can be made very large.
• Only the reflecting side of the primary mirror needs to be perfectly shaped and smooth.