The Rodenstock HR Digaron-SW float 138 mm f/6.5 is an exceptional sharp long focal length lens for adjustable technical cameras intended for a wide distance range from infinity up to an image scale 1:5 (β' = -0,2).
The optical design with eleven lens elements in ten groups is very complex for a prime lens. It has the highest possible resolving power extremely close to the diffraction limit. This is not only achieved across the entire field  – but also to the edge of the large 110mm image circle to allow for lens shifts and tilts.
The rotation of the focusing ring automatically controls the floating elements group and all aberrations are therefore minimized throughout the whole focusing range.
Even with extreme camera movements (shift and tilt) this lens provides an unprecedented sharpness to the corners as proven by the MTF curves given up to 80 lp/mm on the following pages 4 to 6. It provides negligible distortion (almost always below 1‰) and a total suppression of the chromatic aberration for perfect freedom from color fringing.
The image circle of the HR Digaron-SW float 138 mm f/6.5 has a constant diameter of 110 mm throughout its entire image scale range. For professional technical cameras, even with the largest sensor formats, this gives ample clearance for parallel shifts for perspective corrections (avoiding or reducing converging vertical lines). This also allows swing and tilt for extended depth of field without excessive stopping down of the aperture according to the Scheimpflug rule.