The zeiss 21mm f28 t biogon zm silver lens offers outstanding performance and extreme resolving power even when shot wide open with virtually no distortion excellent control of flare and ghosting and superb contrast rendition across the entire frame the slim lens design is easy to grip and focus and uses a standard 46 mm filter diameter similar to many of the other zm lenses and allows filters to be interchanged between the lenses the lens is rangefinder coupled for easy focusing and the