is a specific kind of: device.

is a broader term that covers: autofocus | biprism | camera lucida | coelostat | collimator | diffraction grating, grating | diffuser, diffusor | finder, view finder, viewfinder | Kerr cell | laser, optical maser | lens, lens system, lense | Nicol prism | planetarium | polarimeter, polariscope | optical prism, prism | projector | Rochon prism, Wollaston prism | stereoscope | viewer ... show more.