A pinion engages a rack on a slide. Focusing is achieved by turning a knob or wheel, which moves the lens or image panel. Radiography is the technique of using X-rays, gamma rays and charged particles to form shadow images on photographic materials. Used in medical and industrial research because of its ability to penetrate opaque objects. Rangefinder is a focusing system which measures the distance from camera to subject.
Rapid fixer is a fixing solution that uses ammonium thiocyanate or thiosulfate instead of hypo.
Rapid rectilinear is a lens system composed of two matching doublet lenses, symmetrically placed around the focal aperture. It was introduced by Dallmeyer and Sternheil and removed many of the aberrations present in more simple constructions. Rear curtain sync is when the flash fires an instant before the second or rear curtain of the focal plane shutter begins to move. When slow shutter speeds are used, this feature can create a blur effect from the ambient light, i.e., patterns following a moving subject with subject movement frozen at the end. Rear focus refers to the focused area behind the picture's subject.