What are the advantages of a high resolution spectrometer?
The high resolution spectrometer might be used to search for very small Doppler shifts. The discovery of planets near stars has been done by careful measurements of Doppler shift. The high resolution spectrograph tends to be a large, heavy and sensitive piece of equipment. Often they are placed at the Coude focus of the telescope. The disadvantage of the Coude spectrograph is that it requires more light to detect the spectral lines. This is because the same light is spread across a longer color spectrum and because at the very long focal length a very small angle of the sky is overly magnified onto the spectrometer slit. At the Keck Telescope the spectrograph is used at a lower F ratio ( shorter focus ). To have the high resolution with high sensitivity requires a very large diffraction grating. Also to have the spectrograph at a shorter focus the spectrograph is at the top of a platform beside the telescope and the accurate positioning of optical elements is maintained by precision electronic servos.