Distortion image at corners is common with wideangle lenses, but this particular lens is especially made for Distortion Free based on the sophisticated lens formula which produces a resolution power of *350-line at center. Mounting threads is 55mm. Front filter size is 72mm. Nominal 0.66X(Actual 0.66X/diagonal, 0.66X/center).Optional Sizes/Weight : 75mm x 39mm 178g* MTF 30%. Equivalent to 1890-line/TV(1/4" CCD),2520-line/TV(1/3" CCD).