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I never realised there were lens up for review on dooyoo. I've reviewed a few cameras, I thought I'd add my two cents to a few of the lens I have.
Sigma make a good range of lenses, this is a macro lens. It works with a 1:1 ratio and measures at around 70mm (7cm). used for taking pictures of smallish subjects at a close range, say 5inches to 20 inches. At 70mm its one of the smallest macro lens's I've seen, I dont notice any dissappearance in quality due to this, however. The lenses are designed realistically for D-SLR's, I've never had much luck with these and a traditional SLR, though this isnt really an issue anymore for most.
The company sell versions of this lense for different cameras, they're essentially the same, just with a different fitting to attach to the camera. They're some of the best fitting lenses ive come across. Some of the canon ones I use with a canon camera are TERRIBLE.
One of my issues with the lens is its lack of... internal focusing, I think is the term. Basically, rather than all of the focusing going on inside the lens, the lens changes length to accomodate this. This is the trade-off for having such a short lense.
In terms of image quality, it's pretty good. I've had some beautiful shots of things closeup, but even for other things such as close portraits or indoor shots, it performs well. Anything too brightly lit however produces awful glare on the lense.
In summary, this lens is great for close-ups. If you need something a bit more professional then I think sigma do a range of better lens's, over 100mm that have internal focusing etc. These might be more suitable. The images from this however, are wonderfully sharp and clear, only failing when theres a silly amount of light shining into the camera.
About the lens:
This is one of Sigma's range of lenses - at 70mm it's one of the shorter macro lenses on the market, many coming in at around 105mm. It has sigma's EX technology, from Sigma's website this means "The exterior of this lens is EX-finished to denote the superior build and optical quality, and to enhance its appearance."; the DG means "These are large-aperture lenses with wide angles and short minimum focusing distances. With an abundance of peripheral illumination, they are ideal lenses for Digital SLR Cameras whilst retaining suitability for traditional 35mm SLRs.".
This is a 1:1 macro lens, allowing good images of very small subjects.
This feels a lovely lens to hold - it's quite a small lens but feels sturdy, it's not a lens you'll need to worry about using. The focusing action is very smooth and works well on my D90.
This lens does not have inner focus, meaning the lens length does change as you focus/zoom with this lens, this is quite common on certain lenses and rarely will cause a problem, but may bother a few people. It doesn't have sigh speed focusing technology, that said it does focus at a reasonable speed. It also has a focus limiter if you want to limit the range.
There are versions for Nikon, Canon, Pentax, Sony/Minolta and Sigma that I can find. Online this seems to retail new now for between £350 - £400 (found at Warehouse express currently at £344.99) or can be found at times second hand for less.
Whenever looking at lenses this is a primary concern for most people - I have found the image quality of this lens to be superb, easily as good as you'd expect from a Nikon, Canon etc. versions. It gives very sharp images and good details in the pictures, nothing more I can want from a lens.
As well as a great macro lens, this makes a beautiful portrait or all-round lens!
Overall if you want an easy to afford Macro lens, this is a great one to go for - Sigma also do a 105mm version and a higher spec 150mm macro lens as well.
Overall this is a great lens that comes in at a good price.
Battery life I've given 5 but is obviously not relevant, ease of use loses 1 bar for the fact the lens length changes when focusing.