Comparison of Pentax 17-70mm ƒ/4 AL IF SDM SMC DA and Sigma 18-50mm f/2.8 EX DC

Attribute	Pentax 17-70mm ƒ/4 AL IF SDM SMC DA ×	Sigma 18-50mm f/2.8 EX DC ×
Filter Size (mm)	67	67
Notes	Included Accessories: Lens Hood	Available AF Mounts: Sigma, Canon, Nikon, Minolta, Pentax, Four-Thirds
Closest Focus (m)	0.28	0.28
Magnification Ratio (x)	0.31	0.2
Type	Standard Zoom	Standard Zoom
Length (mm)	93.5	84.1
APS Equivalent	25.5 - 105mm	1.5x: 27 - 75mm; 1.6x: 28.8 - 80mm
Zoom System	Rotary	Rotary, non-telescoping
Image Circle	APS-C	Image Circle
Focal Length (mm)	17.00 - 70.00	18.00 - 50.00
Brand	Pentax	Sigma
Name	Pentax 17-70mm ƒ/4 AL IF SDM SMC DA	Sigma 18-50mm f/2.8 EX DC
Weight (g)	485	445
Aperture (f)	4.00 - 22.00	2.80 - 22.00
Diaphragm Blades	7	7
Diagonal Angle of View (degree)	23.00 - 79.00	27.90 - 69.30
Lens Construction	17 elements in 12 groups	15 elements in 13 groups, including two aspherical elements and one Special Low Dispersion (SLD) lens
Diameter (mm)	75	74.1
Focus Details	Internal; SDM with Quick-shift Focus System	Internal focusing system