Comparison of Carl Zeiss 18mm f/3.5 Distagon T* 3.5/18 and Sigma 20mm f/1.8 EX DG Aspherical RF

Attribute	Sigma 20mm f/1.8 EX DG Aspherical RF ×	Carl Zeiss 18mm f/3.5 Distagon T* 3.5/18 ×
Diagonal Angle of View (degree)	94.50	99.00
Notes	Available AF Mounts: Sigma, Canon, Nikon, Minolta, Pentax	Available SLR mounts: Canon EF (ZE), Nikon F (ZF, ZF.2), Pentax K (ZK). Lens shade included. Nikon ZF.2 version includes CPU interface for autoexposu
Aperture (f)	1.80 - 22.00	3.50 - 22.00
Magnification Ratio (x)	0.25	0.083
Filter Size (mm)	82	82
Type	Wide Prime	Wide Prime
Closest Focus (m)	0.2	0.3
APS Equivalent	1.5x: 30mm; 1.6x: 32mm	1.5x: 27mm
Lens Construction	13 elements in 11 groups, including 2 aspherical elements	13 elements in 11 groups
Image Circle	35mm	35mm
Focal Length (mm)	20.00	18.00
Brand	Sigma	Carl-zeiss
Name	Sigma 20mm f/1.8 EX DG Aspherical RF	Carl Zeiss 18mm f/3.5 Distagon T* 3.5/18
Weight (g)	520	470
Diameter (mm)	88.6	87
Length (mm)	89.5	84
Diaphragm Blades	9	-
Focus Details	Internal (Rear Focus) with Dual Focus mechanism	Manual focus only