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Sigma 28-70mm f/2.8 EX DG IF Aspherical Lens for Sigma SLR Cameras | List Price: $379.00
Discount Price: $379.00
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Brand: Sigma
Binding: Electronics
Features: - Zoom lens with Sigma AF mount
- Special low-dispersion glass for high image quality
- 28 to 70 mm focal length
- f2.8 maximum aperture
- Inner focusing system allows add-on hoods and filters
Excellent resolution and color--auto focus hit and miss [Posted on 2008-02-11]
I bought a Sigma 28-70mm EX lens a few months ago from Adorama and have been using it on a Sigma SD14. Auto-focus is hit and miss, too often focusing well past the infinity mark on the lens--and producing blurry foregound images. Auto-focus problems seem to be common with Sigma lenses and the solution is to send them back to Sigma for calibration. I just turned off the auto-focus by a small button on the lens and manual focus using the markings on the lens (in manual focus, the focus ring isn't very firm and is easy to move accidently, so just take care when shooting). Manual focus to infinity results in very high resolution, sharp corner to corner images throughout the zoom range. One online review of this lens suggested the best optical performance was found at F11. I found excellent results anywhere between F8 and F11.
The lens is 35mm equivalent to about 48mm to 120mm on the SD14. The wide end always seems not wide enough--but the lens really is just a good normal lens with moderate telephoto. Images look yellow in the camera view finder, but this yellow tint in the RAW converted images isn't really apparent--Sigma RAW files on initial conversion are already oddly other-wordly warm anyway and adjustment in white balance works wonders getting to reality or somewhere in between.
The lens feels solid and well built. Infinity focus remains the same focus ring position through the whole zoom range. Some CA is apparent in images shot at the wider end of the lens (easily removed with CS3 raw tools) and hardly detectable in images shot at the mid to telephoto end. The optical performance, despite the lens having to be stopped down to F8 to F11, makes it a keeper for me.
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