Like the Sigma 24-70mm f/2.8 EX DG Lens, the Sigma 28-70mm f/2.8 EX DG Lens is a well-built, well-spec'd lens with a value price. But, giving up 4mm of focal length range on the wide end results in a much more compact lens. In addition, the 28-70 is priced noticeably lower than the Sigma 24-70.
Pictured above from left to right are the Sigma 28-70mm f/2.8 EX DG Lens, Tamron SP 28-75mm F/2.8 XR Di Lens, Sigma 24-70mm f/2.8 EX DG Lens and Canon EF 24-70mm f/2.8 L USM Lens. The same lenses are shown fully extended below.
The Sigma 28-70 is a solidly built lens. As it often does, solid translates to a rather heavy weight for the small size. Measuring a trim 2.9" x 3.4" [74 x 87.2mm], the 28-70 weighs 18.1 oz [510g]. At 70mm, the lens barrel extends an additional 1" [23.4mm] or so. I really like the size and shape of this lens - It is comfortable to hold. I am not found of Sigma's matte finish and texture [a purely personal opinion], but most of this lens' barrel exterior is covered by the rubber-coated, smooth-operating, nicely-sized zoom and focus rings.
Although the focus ring is smooth, I found just enough play in the ring to make manual focusing more difficult than it should be. I like the forward-positioned focus ring as I generally hold my lenses near the rear of the barrel - and don't want to accidentally change the focus setting or have the ring turn in my hand during autofocus. The Sigma 28-70mm f/2.8 EX DG Lens does not support full-time manual focusing - and the focus ring physically turns during autofocus. A distance window is not provided nor is necessary as the distance information is marked on the always-live focus ring. Autofocus is loud but reasonably fast - and is consistently accurate on stationary subjects. AI Servo performance on active subjects proved to be poor - with few keepable shots. Low light situations proved difficult for the 28-70 as well. As internal focusing is employed, the 28-70 does not extend during focusing.
The Sigma 28-70 is very soft wide open - especially in the upper half of the focal length range. I don't consider the results useable at and above 50mm until the lens is stopped down to at least f/4 where the full frame corners are still soft. Performance at f/5.6 is better. This lens performs best at 28mm where the results are decent.
CA [Chromatic Aberrations] are very well controlled, flare is not. Colors have a strong yellow cast to them - it is quite apparent when comparing photos from the Sigma 28-70mm f/2.8 EX DG Lens and a high-end lens such as the Canon EF 24-70mm f/2.8 L Lens. Moderate barrel distortion is present at the wide end and disappears by 40mm or so. Vignetting results are normal for lenses with specs similar to the 28-70 with full frame users noticing some corner darkening when shooting wide open. Like the Sigma 24-70, I find the Sigma 28-70 to overexpose by about .2 f-stops on average.
The Sigma 28-70mm f/2.8 EX DG Lens features a fast, fixed 9-blade aperture ranging from f/2.8 to f/22. Again, you probably will want to avoid f/2.8 over most of the focal length range.
A 67mm filter diameter keeps the Sigma 28-70's objective end reasonably small. Not many lenses share this filter diameter [the Canon EF 70-200mm f/4 L USM Lens is one of them], but filters of this diameter are not too expensive. Circular Polarizer filter users will appreciate the non-rotating front element which also allows the use of an ideally-shaped [petal] lens hood.
Sigma's zoom ring turns the opposite direction from Canon's zoom lenses - neither is better unless you are very used to one direction or the other. A zoom lock switch locks the lens in the retracted position. This switch is not necessary unless this lens breaks in a great deal after use.
Pictured above from left to right, the Sigma 28-70mm f/2.8 EX DG Lens, Tamron SP 28-75mm F/2.8 XR Di Lens, Sigma 24-70mm f/2.8 EX DG Lens and Canon EF 24-70mm f/2.8 L USM Lens are with lens hoods in place. The same lenses are shown extended below.
With a minimum focusing distance of 13" [33 cm], the Sigma 28-70 has a maximum magnification of .23x. It will focus close enough for nice pictures of flowers and other similar-sized objects.
The included small, plastic, inside-ribbed lens hood extends and retracts with the lens [like most lenses with this focal length range]. There is not enough room for me to comfortably pinch the cap release when the hood is installed, but I am able to do so. This is a nuisance if you are installing/removing the cap with any frequency. A nice padded nylon lens case is also included.
The Sigma 28-70mm f/2.8 EX DG Lens is available in Canon [reviewed], Pentax, Minolta, Nikon and Sigma mounts. Disclaimer: There are some potential issues with third party lenses. Since Sigma reverse engineers [vs. licenses] manufacturer AF routines, there is always the possibility that a new body might not support an older third party lens. There are examples of this happening in the past. Sometimes a lens can be rechipped to be made compatible, sometimes not. Second, there is the risk of a problem that results in the lens and body manufacturers pointing blame at each other. However, Sigma USA's 4-year warranty is far superior to Canon's standard 1 year warranty.
Review update Nov 17, 2010: I just received an email from "Dan" with the following bad news: "I have this lens and it does not work with a canon XSi [back focuses]. Sigma informs me that this is a ROM issue and cannot be fixed."
The Sigma 28-70mm f/2.8 EX DG Lens is a very well built lens for a reasonable price. Primarily due to mediocre image quality, I do not intend to include this lens in my Canon General Purpose Lens Recommendations. If you consider this an f/4 or f/5.6 lens, you *might* be happy with what you get for the price.
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