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I bought this lens not really knowing for sure how often I'd use it, but the price was right and lenses tend to hold there value reasonably well so I could always flip it if I didn't find much use for it. The build quality is adequate, it's heavy, but somehow just doesn't feel as solid as its weight would suggest. I can't comment on it's long term durability because despite owning the lens for nearly 4 years, it just didn't get very much use. Which brings me to my next point... The lens is priced at a good place for a 'decider', that is, to help decide if you need the range afforded to you when using 300 millimeters of pure light-concentrating power. I didn't. But I got some good shots with this lens and it served as an affordable learning experience. The maximum aperture of f/4 (f/5.6 at the long end) is slow, so if you're planning to use this to photograph the eyebrow of someone at the other side of a nightclub you might want to look elsewhere. Most people will be using this for sports or maybe a nice safari trip (you lucky devil), and on a sunny day, the lens would cope well in either of these situations. It might not be so great for Sunday morning rugby in the height of winter though. I had the Sony version, which meant the lack of integrated image stabilization was a non-issue as Sony's Alpha range has this built into the camera. I imagine that if using a Nikon or Canon SLR though, that a steady hand or a tripod would be a necessity. Focussing isn't as fast as I'd hoped, but with a focal length like this, there's a lot of glass to move, so it's not entirely surprising. And while autofocus isn't as fast as many other lenses, it's not unusable. But for fast moving subjects, it may be a good idea to whack up the aperture and focus manually. Image quality is better than expected at the price-point, it's not a pro lens, and images are a bit soft and show some chromatic aberration. A little post processing can do wonders with this, and I don't think anyone purchasing a lens at this price would complain. All in all, it's a worthy way to spend your money, but if it's a toss-up between this and a more general purpose lens think hard about whether you need the range. I know I certainly didn't. And yes, I did flip it in the end and for almost what I paid.
The Sigma 70-300mm Super APO DG Lens is a very reasonable zoom lens for the beginner to intermediate photographer. The product comes with a lens hood and case for its price, which makes it very good value, much better than a similar Canon lens for example which costs more, comes on its own, and probably charges you about £20 for the rubbish bit of plastic that it takes to make a lens hood. The aperture on this lens is F/4-5.6, which is not particularly fast, and therefore generally I recommend you either use it when there is a LOT of light (unless you are at its widest end) or on a tripod. What makes this lens great value is the included macro mode (not with all models, make sure you check), but this is hit and miss. It's better to have it than not at all, but it's only "half macro", the pictures are of variable quality and a bit washed out. Even worse, the macro button will often get stuck when you are on auto focus, and will require switching to manual focus, altering the focus ring, and then finally being able to switch back to normal mode. This is a very bad design flaw. That said, I've managed to get some decent shots with this, I just needed good light, and a contrast and sharpness boost in your editing software of choice improves the picture after it is shot. The range of 70-300 is also extremely useful, making a good addition to a kit lens (although beware that on a non-full frame camera the minimum focal length will be over 100 depending on the model). Overall, if you are on a budget or not hugely focused on long range sports photography or macro, this is a good lens to buy. If you love macro though, buy a dedicated macro lens, and if you love shooting things at a distance, purchase a lens with Image Stabilisation.
A good value alternative to the Nikon or Canon 70-300 lenses. This lens outperforms the old nikon 70-300 G lens. It does not have vibration reduction/image stabilisation like some of the nikon or canon alternatives, but at the price you can't really complain about that. You just have to make sure you keep the shutter speed up, and have good 'long lens technique' using a tripod, monopod, beanbag etc. It is pretty sharp even wide open, so makes a great cheap lens with reasonable reach. Focuses usefully close too, especially the macro version, so is great for chasing butterlies and dragonflies about. The focus isn't particularly fast, and it can hunt a bit too. Also, as it isn't HSM it will not focus with some of the low end nikon dSLR's such as the D40 and D60 as they do not have a focus motor in them and neither does the lens. This lens is great for a budget introduction into getting a telephoto lens, and I have had one for about 4 years but now have upgraded to nikons 70-200 f2.8 VR. It is a testament to this lens that I have been able to last 4 years with it without needing to upgrade.
The Sigma 70-300mm lens sold as a less expensive alternative to the Cannon EF lenses and retailing at about half the price of its counterpart (When I bought mine). In general it is a solid lens a little on the heavy side and a little sticky with the zoom. Unlike the EF lenses the Sigma's do not have image stabilizers incorporated, hence the lighter cost, so you will have to find other ways of dealing with camera shake (tripods for example). The Sigma also seems to get a little confused with the auto focus and will pull in and out of focus until it gives up, switching to manual focus is not too much of a pain for me, but if you are counting on a good auto focus feature, this may not be the lens for you. Having said that picture quality is clean and sharp and if like me you aren't able to break the bank on equipment or you are just starting out then this is a good lens to go for.