170-500mm f5.6-6.3 APO

Within its limits, I consider this an excellent lens for someone on a budget.

For under $500 I don't believe you can do much better unless you find a Tokina or Sigma prime that is just a right on example. I bought mine used through KLH and I am beyond pleased with the condition, there is nothing you or I could tell between new and their excellent rating. In bright daylight with subjects under 25' in distance it does an excellent job and I'm more then satisfied. In cloudy or longer distances ( more extreme circumstances where you should get what you pay for ) you can have problems with focus hunts, ragged edges, and Chromatic Aberration/fringing. Let's be real...you pay more money to solve these problems and when you do pay for it, it better solve it. Is it worth 3, 4, 5 times as more to you to spend that much money? I use it hand held in good light, on both a Nikon D80 and D70. It's lightweight enough not to wear you out lugging a 2.8 or other big metal tubed long focal length lens. Not only will a budget minded person save and achieve great results, you'll have a good time doing it - just keep the price - performance ratio aspect in mind. If you want budget minded practical performance under $500 that produces sharp enough images look here. If you need to look fashionable or have the money then look elsewhere... but please, I've tried the Tamrons and they simply aren't as sharp and do not deliver the same colors.

This lens will take great photos if used within its limitations. It is best for pictures of stationary birds in good lighting, taken with a tripod - excellent for "bird on a branch" pictures. In these situations I have been unable to tell the difference in quality between shots I have taken with this lens and with a canon 400 f5.6 prime - I have to look at the exif data to tell. It does autofocus slowly and is not too good for flight shots. It is also not the greatest for low light conditions and good long-lens technique must be used. For its price, I think it is a great deal.

I have this lens along with many others and i love using it great lens for birding and is certanly better than the tamron or Bigma.

I purchased one of these for about 2 months before selling it and getting the Tamron. I find this lens to be quite soft compared to the Bigma or Tamron zooms. I suppose if you get the bird to fill the frame where you don't need to crop, you'll be ok. Maybe mine was a bad sample, but I'd not recommend it and think there are better choices in this price range.

bought this lens off ebay for 275.and for the price,it rocks.

It is a great lens for the price. We all want the reach that 500mm brings but not all of us can afford 4000 for a decent piece of glass, so this lens fits the bill nicely.
Mine is the APO DG version and while it's not 100% sharp at the 500mm end, it is certainly excellent value for money and is fine optically along the rest of the focal lengths. I have no plans to offload mine until I can afford something better.

I bought this lens used to give it a try with my D70 & D200. It is a small and lightweight lens, making it easy with which to travel. The range is useful, but difficult to get through due to a stiff and jerky zoom ring. Despite the stiff ring, there is still zoom creep. The focus ring is flimsy and poorly-placed (at the base of the lens). Lack of manual focus-override is annoying after using Sigma EX and Nikon AF-S lenses, but typical of lower-end lenses. I found that objects within 5 meters recorded well through the lens, although with limited sharpness; beyond 5m, the images were always blurred, even on a tripod with remote-release. Color and contrast were also less-than-spectacular. I don\\\'t expect any better from a lens in this price range, but compared to an EX lens like the 100-300 f/4, it falls way short.
I tried it with Sigma\'s EX 1.4X tc. There was too much light-loss to be practical in less-than-optimal lighting, and autofocus was lost. The image was soooooo soft, even in the viewfinder, I never tried it after the first time.

The reason I give this lens full marks in review is not because it does not have shortcomings, but because the price/performance equation leaves it so far on the positive side that despite the shortcomings it is undeniably great value. Not everyone (especially me!) has the budget or bravery to invest in the large Canon primes - you obviously get greater results with these. But for the hobby and prosumer birder, this is an ideal entry point into super-telephoto, and they are frequently available second-hand.
I was aware of Sigmas advertising claim that their APO glass virtually eliminated chromatic aberration, and at first thought - Yeah, right, I would have to see that proved before I believe that! -. But it has been, in two years experience using it with a Canon 20D, and after tens of thousands of bird photos, a claim I happily reinforce.
Sharpness and feather detail are excellent for its class throughout the range, and consistently good for a zoom. Sweet spot from f8-f14, more than that is weaker. Mostly I use it at the 500mm end (bird photography usually demands the longest reach, at least in the wild). It is consistently sharp when I use it on a monopod, but like all lenses, it does not necessarily do all the work for you - you still have to work at technique. I also use a Canon L 35-350, preferable for flight shots, and when using flash, and when a nice bokeh is essential (the Sigma 170-500 is okay but not dazzling in this regard).
The weight is low enough that I can carry it all day long on a long hike without pain. The low price commends itself to use in situations where there is reasonable danger of immersion or damage by dropping, even if you have better lenses - I have been up to the waist in seawater, thigh deep in swamps, and clinging to rock faces in the pursuit of bird shots - and I know that if I lose this baby it will not bankrupt me, and I will be able to replace it!
Deficiencies? I will mention them but not labour them. Lack of focal length lock - disconcerting to have it flop out to 500mm with a clunk if I forget to extend it manually before lowering it, and I worry about the effect of the jarring on its life-span. The lens hood is cheap plastic and its mounting not robust. Slow in low light. You can use a Sigma tele-extender 1.4x (the manufacturer says no, but it does work) but I would not recommend it - not much better than careful upsizing if you have the Photoshop technique or software like Genuine Fractals.
In summary, I love this lens for what it does and do not lament the deficiencies. It addresses a large market need. If you want better, pay more - a LOT more. It has changed my world and given me some great experiences and some beautiful images. For those wanting to progress to top glass, but unsure about whether to pay big bucks - consider trying one of these as an intermediate step. I consider buying a second one as a spare. Well done, Sigma!

Cheers, Bruce

i use this on my 350D, and they are happy together handheld or on a tripod. images are detailed and crisp, once you get used to the right hold/balance. i paid 440 for mine.

I bought this lens a couple of years ago for the Nikon F80, now used on the D100 which turns it into 750mm at full zoom. The zoom action is a little stiff, but I put that down to the barrel length. It\'s the only long lens I\'ve used and can produce sharp images if I get the technique right!. Yes more speed would be nice but you would be in a higher price bracket.. highly recommended

Used in conjunction with the digital Canon EOS 300d this now gives me a zoom lens ranging up to 800mm (all images magnified x1.6 when used with 300d) and with a minimum focusing distance of 3.2 metres! Excellent optical clarity, good lens hood but needs a (protective) UV filter of 86mm to cover the front element which stuck another 50 on the cost - living on bread and water for the next six months.

A wonderful lens....is easy to use....recommed highly

works fine for me right now,
i wonder if it does when i switch tot digiSLR-photography next year!

excellent for wildlife, i use it with a 1.4 converter sometimes but then you have to use manual focus. pictures are very sharp would recomend it.