@aarslan i'm a nikkor 105 owner, mainly used on nikon D5100, (which has the same processor with the D7000), which equates to 135mm f4-8 lens. Tamrons and Sigmas are better as cheaper alternatives of flagship nikkor lenses: 24-70mm/f2.8, 70-200mm/f2.8, etc... or wides. The 105mm is one of the more affordable lens by nikkor and has min. focus at 4-6cm and decent low-light performance. The MTF charts of the lens speaks of its capabilities for sharpness and contrast. I think it is the ideal match for the D7100, just get the G model v2, as the AF is better. along with a 55mm macro for wides, you should be all set. As your subjects are photomacrography, i would actually suggest that you stick to the nikon system, rent the 105mm, initially, if necessary. The better colors of Canon systems are always tempting and the canon bodies have upped their game as of recent, mostly benefitting the color-concerned and/or the video-maker . However, Nikon is still the largest producer of microscope elements, which i believe is the core of their optics manufacturing concern and sport the largest ecosystem of compatible accessories and parts for the SLR and DSLR lineup, esp. suited for technical imaging. Hope this helps.