Distagon T 18mm f/4 is a classical Zeiss manual lens. The optical construction
of the lens consists of 10 elements in 9 groups, including a single floating low
dispersion glass element for correcting chromatic aberration at close range. The
build quality of the lens is superb, a common trait of Zeis lenses in mount
barrel is metal and both focus and aperture rings are rubberized. The lens looks
as if it has an inner focusing mechanism, but the lens barrel actually extends
(very) slightly when focusing towards closup. The lens is relatively compact and
lightweight (for such an ultra-wide lens), measuring 7.0 x 5.15cm
and weighing 350g. The minimum focusing distance is 30cm and the
minimum aperture is f/22. The lens accepts 86mm screw-in type filters, but requires
a 70mm/86mm adapter ring. On an APS-C cameras with 1.6x crop ratio, the lens has
field of view similar to that of a 28mm lens on a full-frame body.