Dual speed focuser

rdf:langString Dual speed focuser

rdf:langString The Dual speed focuser is a focusing mechanism used in precision optics such as advanced amateur astronomical telescopes and laboratory microscopes. A dual speed focuser can provide two focusing speeds by using a set of co-axial knobs, one for fast focusing and another for fine focusing when the film or CCD is near the perfect focal plane. This is different from the two separate focusing knobs seen on low level microscopes. Another common reason to employ a dual-speed focuser is with the use of short focal length eyepieces, where the depth of focus is short, requiring critically accurate focusing. A dual speed focusing mechanism is often combined with a Crayford focuser, forming a Dual speed Crayford focuser in order to eliminate backlash during fine focusing.