The most significant portion of the solar telescope used at Mojave Solar is the Magneto-Optical Filter (MOF).
The MOF used at Mojave Solar allows the passage of light in two narrow wavelength ranges ("passbands"), on either side of the potassium D solar absorption line (769.9 nm). By measuring the difference in intensity in each of these passbands, we can determine Doppler shifts in the lines caused by motions in the solar surface, and also measure the Zeeman splitting of the lines caused by the solar magnetic field. Light passing through the MOF is imaged on a CCD. These images are then used to create maps of velocity and magnetic field over the Sun's surface (Dopplergrams and magnetograms).
Currently, the MOF is in use at only a few locations around the world.