http://www.nikonchat.com/nikon-lenses-18-200-vr/

Which of these Sigma lenses should get a macro for my Nikon DSLR?
I'm thinking of getting one of the macro sigma objectives mainly at the lowest cost in comparison with Nikon macros. Correct me if I'm wrong but I heard that they are more or less the same picture quality. My question is regarding to the focal length. That I'm considering are the macro 50 mm, 70 mm macro and 105 mm macro. I'm leaning more towards the mm, since in the lower focal length setting price is 105 as Nikon, so you can get a nikon, nikon, but the 105 mm is twice that of the Sigma 105 mm macro. So it would take was a given a 18-200 VR, and a mm f / 1,8 and 50. Camera is a D90.
That really depends on what is going to shoot. The 105mm is better if you plan to take pictures of flying insects and can not be fairly close. The 50 mm is pretty, but it has one. The 70 mm is also very beautiful because it is the middle term and may serve as a nice macro lens for insects and flowers and, as such, and a good portrait lens sharp. 70 mm is ideal for me at least for portraits because it gives a more flat. Another thing you want to see on the increase. 1:1 is nice, but not sure if that not everyone can do macro 1:01 because I am a canon fan. Evaluate their use and see what works best for you. We must also keep in mind about the opening, it is generally best for low light and depth of field control. Personally, I, I went with the 70 mm because it is a good combination between a portrait lens, and macro shots.
Toronto Air show 2009 Nikon d90 18-200 mm lens IN HD