While I don't often make changes, I'm constantly analyzing my lens kit and thinking over improvements. Camera is a D800E and lenses are Nikon 20mm f1.8G, Nikon 24mm PCE, Sigma 35mm f1.4, Sigma 50mm f1.4, Nikon 105mm Micro VR. Likely next change will be eliminating the 20mm and replacing with SIgma 14mm f1.8. We'll see. I had another thought as well--swapping the Sigma macro for the Nikon. On paper the two lenses perform the same. I'm actually happy enough with the Nikon, and there does't seem to be much difference between them with one exception. The Nikon brings ~$200 more on ebay than the Sigma. If it's true I'd not see much if any difference between the two, it would be logical to sell the Nikon, buy a used Sigma, and pocket the $200, would it not? I was carrying the Nikon 85mm f1.8G as the longest lens I normally carry (Nikon 80-400mm AFS when longer is anticipated,) but I found I just didn't use the excellent 85mm f1.8G as much as I thought, and sold it. The 105mm is very versatile and does duty as a macro lens, a portrait lens, and a long tele. My lens selection is assembled with the philosophy of best available and most versatile as a system.
I have the Sigma 105 OS. The OS is not intrusive but generally works very well even at close to 1 to 2 mag ratio. Wide open at normal distance is sharper than the Tamron 90 VC f017. Focusing is as fast as you can get with a longer macro lens. I don't have much luck with it shooting cycling races...that's just pushing it. Otherwise with normal active subjects, the focusing is fast and accurate.
Here is my recent macro shot with the Sigma. Is a 5 shots focus stacked. Strobed at F16. DFrostyDawn3blooms1 by vracing, on Flickr
I have and love the Sigma 105mm HSM OS, but I'm not sure if the AF is quite as fast as the Nikon, and it doesn't have a rear gasket. If those differences don't matter the optical differences should be pretty minimal and it's a good trade.
My Sigma 105 OS was everything, and it takes great macros, until I held the Nikon 105 VR. If, in addition to image quality, build matters to you, then keep the Nikon. It's much better made.
