http://www.nikonchat.com/18-200-nikon-vs-sigma/
Sigma vs Nikon SLR lenses, it is worth paying double for Nikon?
Need to get a 105mm macro, Nikon is twice the sigma. Is it penalty to pay double? It will be a D90 body. I also have a 18-200 mm Vr, I'm thinking that eventually replace with a 70-200 f/2.8 and 18-55 mm f / 2.8. Once again the sigma which are half the price of Nikon. So my main question is: Do I really have to pay double to get the results I want? What really is the difference between say, a 70-200 mm f / 1.8 for Nikon and Sigma Nikon makes the $ 700 more, which is a large sum. I guess my other question is Is it worth replacing the VR 18-200 mm with 2 lenses that are 2.8 to cover the same range and pay a lot more instead of keeping the 18-200 VR?
Yes and no. Lenses others are much, much cheaper than the Nikon equivalent, but in almost all cases, do not do as well. It is a small difference that is likely to be only when shooting test charts in laboratories, but the difference is small enough for a professional to choose the more expensive lens. Even for the amateur, I can safely say that you should try both versions and see for yourself what you like best. Some people like a do-it-all lens that covers a broad range from wide angle to telephoto. They are willing to sacrifice some image quality in low light performance and the versatility they get in return. If you have the money, I say go for it. But consider this, a "fast" f/2.8 is nothing compared to a f1.4 objectives. Although it lacks the ability to zoom, you gain much more in the shutter speed (4 times faster), superior sharpness and less distortion than zooms. Not to mention that they cost much less than a fast zoom. Only some suggestions for saving money.
Sigma 18-200 3.5-6.3 DC OS
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