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Full Version: Tamron Announces SP AF17-50MM F/2.8 XR Di II LD ASPHERICAL [IF]
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What a mouthful! But yeah, Tamron now has a direct competitor to Sigma's 18-50mm f/2.8 EX DC, which has been quite popular and has been reviewed by our very own slejhamer in the past. It's also an alternative to the 28-70 f/2.8 for users who want a fast constant aperture, and also a wider angle of view for digital use.

For once the Tamron and Sigma equivalents don't look like clones of each other in terms of specs. If we're just comparing specifications, it looks like that Tamron wins marginally in every area - size, weight, wider angle of view, minimum focus distance, magnification ratio. It would be very interesting indeed to see how it stacks up optically!

Tamron 17-50
Lens Construction (Groups/Elements): 13/16
Angle of View: 78°45'-31°11' (APS-C size equiv alent)
Diaphragm Blade Number: 7 (Circular apertures)
Minimum Aperture: F/32
Minimum Focus: 10.6in.(0.27m)
Macro Mag. Ratio: 1:4.5 (at f=50mm MFD 0.27m)
Filter Diameter: ø67
Weight: 398g (14oz)
Diameter x Length: ø2.9 x 3.2in. (ø74.0 x 81.7mm)

Sigma 18-50
Lens Construction: 15 Elements in 13 Groups
Angle of View: 69.3 - 27.9 degrees (SD format)
Number of Diaphragm Blades: 7 Blades
Minimum Aperture: F22
Minimum Focusing Distance: 28cm/11.0 in.
Maximum Magnification: 1:5
Filter Size: Diameter 67mm
Dimensions: Diameter 74.1mm x 84.1mm / 2.9 in. X 3.3 in.
Weight: 445g/15.7 oz.