I have been shooting with this Sigma 70-200mm f2.8 lens for a few days now and I have found it to be pretty good. It’s has a sharp and fast auto-focus, not quite as fast as the auto focus that you would find on the Nikon lens. But, at being a third the price of the Nikon, I think that I can live with it. This lens uses what Sigma calls its Hypersonic Motor or HSM focusing motor, meaning that this lens can be used on more entry-level cameras, such as the nikon d3000 and d5000. The focusing and zooming is all internal on this particular lens, so there is no optical element moving on the outside when you zoom in and out, or focus. The lens stays one length though out the full zoom range. This lens also allows the user to manually override the auto-focus, allowing you to really fine tune the focus, or correct for the occasional back focus problem.
I didn’t have too many issues with this lens back focusing. The only issue that I did have however, was when I was trying to focus on a very small object such as one flower in a large bed. The lens kept focusing on the larger bush behind the flower. This was no problem because I was simply able to correct the focus with the manual override feature that this lens provides.
The optical quality of this lens is very high, I would say it is to be expected though, with a price tag of around $800. The lens appears to be pretty sharp through out its full zoom range. I would say that as you near the 200 mm end, the image does become slightly softer, but not too much to where it is very noticeable. I didn’t notice any vignetting in the photos that I have taken so far with this lens. I did however notice that at the long range of the zoom, closer to the 200 mm mark, there is a very slight amount of chromatic aberration, though it is not really noticeable. Thanks to the large lens hood and the inclusion of Sigma’s Super Mulit-Layer lens coating, this lens does not really have any problems with lens flare or ghosting.
One feature that I think is quite good on this lens is its “Macro” feature, which is in this case more of a close focus feature. I have to say that I am quite impressed with this, lens’s ability to focus on a object that is about 30 inches away from it with surprising clarity and sharpness. Though, not as sharp as what you would see is a true macro lens.
Thanks to this lenses large aperture of f2.8, you can really shoot in some real low-light situations, while keeping your shutter speed up to freeze all of the action and to avoid any camera shake. Having such a large aperture also allows the user to really blow the background out of focus giving the picture a nice bokeh (the out of focus background area in a photograph). Because this lens has a constant aperture of f2.8 through out its entire zoom range, you don’t run into the same problems that you experience with a lesser quality lens with a floating aperture, where your exposure is constantly changing when you zoom in and out.
I would definitely recommend this lens to any photographer. This lens is not quite as sharp as the Nikon, though image quality is still exceptional. I think that it preforms exceptionally for being one-third the price of the Nikon. Though I have not used the Nikon 70-300 mm “prosumer” lens, I would strongly recommend spending the extra money on this Sigma. You’re getting better image quality and faster glass, which in my opinion, is more important than having a longer reach lens. Anyways, on a Dx format camera such as the Nikon d3000,d5000, d90 or d300 you get a zoom range that is 105-300 mm. One issue that I wish that Sigma would address with this lens, is giving it proper weather sealing, but that is the only a slight complaint with this lens. Over all I think that this is a great lens and an exceptional value when you compare it to the Nikon 70-200 f2.8 which goes for about $2,400.