Transmission gratings have specialized uses in spectrometry. Any optical imaging system, such as a camera or telescope, can be converted into a spectrograph by placing a transmission grating in the system, typically in front of the objective lens. Transmission gratings also serve as convenient beamsplitters for monochromatic light sources such as lasers. The efficiency behavior of transmission gratings is simpler than that for reflection gratings since no metals are present to introduce complicated electromagnetic effects and since the angles of diffraction are usually small. Thus, polarization effects are virtually absent.