With the 18-250mm DC OS HSM, Sigma has set a new standard for superzooms. Tamron made a step forward with their 18-250mm, adopted by Sony. The Sigma goes a stage further, reducing distortion levels, improving full aperure sharpness at the long end, controlling CA and vignetting while offering a useful dual choice of image stabilisation methods on the Alpha system bodies. Unlike the Sony, it does not auto-crop when fitting to the Alpha 900 body and can be used at 250mm (only) with full frame coverage, smoothly but strongly vignetting. At all shorter lengths, a circle appears to define the frame; at 18mm, you can crop a 4264 x 2843 image and just avoid corner cut-off, which equates to a 1.42X factor or a 17mm view, really not worth trying! But you can also get a decent square wide-angle shape from the same circle.
Examining the image using the Alpha 900 shows how well the distortion and vignetting have been controlled. Between 35mm and 50mm, the lens is almost as good as you would expect from a prime in that range. There’s a patch of stronger distortion around the 80mm zone, but it reduces as you pass 135mm to leave a class-leading long end.
The price of the Sigma may be a little more than the Sony in the UK, at current street discounts. I would say it’s worth it, but try the lens if you can. The zoom action is nothing at all like the really sweet, light weighting of the Sony. It has resistance and this resistance is not constant, there’s a definite midrange ‘lump’. There is no direct manual focus but the HSM is a positive benefit despite that. It’s heavier, larger, takes non-standard large filters and you must remember when using OS to turn off SSS or your shots will be spoiled. Equally, if you use this lens, you must remember to turn SSS on when switching to other lenses.
Shirley works almost exclusively with one lens, and the Sigma has replaced the Sony in her kit – because of its superior performance at all apertures which makes it Program-mode friendly, no need to set Aperture priority f/8 as a startpoint which we do with the Sony.
I now find we have more Sigma lenses in the working outfits than Sony lenses. This was not intentional. In fact, there are very few real Minolta or new Sony lenses in our kit – the 28-75mm and 17-35mm are really KM rebadged Tamrons, the Sony 18-250mm was always really a Tamron. Just the 16-80mm, 16-105mm, and 70-300mm SSM remain to represent the current OEM offerings in our system.
Postscript: after more than a year of use, this lens continued to be firm and solid in action.
– David Kilpatrick