Comparison of Pentax 17-70mm ƒ/4 AL IF SDM SMC DA and Sigma 28-70mm f/2.8 EX DG

Attribute	Pentax 17-70mm ƒ/4 AL IF SDM SMC DA ×	Sigma 28-70mm f/2.8 EX DG ×
Magnification Ratio (x)	0.31	0.23
Filter Size (mm)	67	67
Focus Details	Internal; SDM with Quick-shift Focus System	-
Closest Focus (m)	0.28	0.33
Lens Construction	17 elements in 12 groups	14 elements in 12 groups, including 4 aspherical and 2 SLD elements
Length (mm)	93.5	87.2
Focal Length (mm)	17.00 - 70.00	28.00 - 70.00
Diagonal Angle of View (degree)	23.00 - 79.00	34.30 - 75.40
Brand	Pentax	Sigma
Image Circle	APS-C	35mm
Name	Pentax 17-70mm ƒ/4 AL IF SDM SMC DA	Sigma 28-70mm f/2.8 EX DG
Weight (g)	485	510
Type	Standard Zoom	Standard Zoom
Notes	Included Accessories: Lens Hood	Available AF Mounts: Sigma, Canon, Nikon, Minolta, Pentax
APS Equivalent	25.5 - 105mm	1.5x: 42 - 105mm; 1.6x: 44.8 - 112mm
Aperture (f)	4.00 - 22.00	2.80 - 22.00
Diaphragm Blades	7	9
Zoom System	Rotary	Rotary with lock
Diameter (mm)	75	74