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Years ago, when fixed focal lenses ruled undisputed, and tele- zooms of the 100-400 range were rare and regarded with suspicion, because at the longest end image quality was rather so-so, Sigma had in its list two very good tele lenses: a 300mm f4 and a 400mm f5.6 labelled as APO MACRO because they had low dispersion lenses and minimum focusing distance (1.2m for the 300mm, 1.6m for the 400mm) that was really short in comparison to similar teleobjectives of other brands. The definition MACRO, if not precise (the maximum reproduction ratio was 1:3,3 for both lenses, thus not in the field of real macrophotography), indicated however that these lenses allowed to make very good close-ups to big insects,, frogs and salamanders, reptiles, flower and other fairly small subject, that stood out of the background and keeping a good working distance (safe for us or for the subject it depends ) . When mounted on a APS-C Dsrl, a nearly true macro reproduction ratio (approx. 1:2) could be reached, thanks to the crop factor of the smaller sensor. And the image quality was very good. Unfortunately these lenses were off list before the digital era and only used samples were available, but they had compatibility issues with digital cameras, mainly concerning focus accuracy. Only in few samples focus errors could be corrected by in-camera fine tuning, some others were unusable due to extreme back/front focus. It was a pity because with a good sample excellent images could be obtained. This picture of a male Banded Darter (Sympetrum pedemontanum) was taken with the old Sigma 300mm f4 APO MACRO These tele lenses were replaced by 70-300 Macro zooms of different brands, that allowed to reach even 1:2 reproduction ratio, but image quality did not keep uo with new high density sensors. And now Sigma suprised all with the new 100-400mm f 4-6.3 Contemporary that shows very good to excellent performances especially at the long end as demonstrated by Mauro Maratta in his reviews here on Nikonland. In addition to the good things already described by Mauro, the 100-400 Sigma has a minimum focusing distance nearly identical to the old Sigma 400mm f 5.6 APO MACRO, that is about 1.6m. This made me curious to try it in close-up photography. The Sigma 100-400 can be easily used hand held even in close-up photography The differences between the old 400mm and the new 100-400 zoom (other than the obvious fact that one is a fixed lens and the other is a zoom) can be quickly and easily explained for what concerns close up photography: Image quality is visibly better in the zoom , with respect to the old 400mm, while the the reproduction ratio (at 400mm) is somewhat lower (1:4 for the zoom vs 1:3,3 for the old 400mm).This is due to a greater reduction of the actual focal length at closer distances (focus breathing) where the zoom at 400mm at the minimum focusing distance is actually a 256mm, while the old 400mm became a 330mm , the difference is not great, but visible. Thus the performances in close-up photography are somewhat lower, especially on full format sensor cameras. For relatively big subjects there are no real problems and the versatility of the lens remains amazing: While for little subjects like the Licenid butterfly below, it shows some limits. Things improve a lot when the zoom is coupled with an APS-C Dsrl camera. The crop factor allow to take more than satisfying close-ups. 100% Crop of the image taken with D7100. Great image quality. Southern Skimmer (Orthetrum brunneum); above, taken with Nikon D610, below with Nikon D7100, same distance. Crop 100% of the image above. You can see elements of the compound eye (ommatidia). Volucella, a large fly. Above D610, below D7100, same distance. The same applies for wildlife. On an APS-C Dsrl the zoom becomes a 200-600 equivalent , light and portable. Coupled with an high performance Dx camera like the Nikon D500 , the zoom may make a perfect combination of good quality and portability especially for BIF (Bird in Flight) photography. These Ibises aren't really in flight, but they give an idea. Performance with close up achromat lenses. A way to bypass the smaller reproduction ratio is to mount a close up achromat filter/lens, with the zoom set at mid-range (200-300mm) where the combo works at its best. In the following images I coupled the zoom with a Canon 500D achromatic close up lens ( 2 diopters) that combines excellent quality with moderate strength. Results made me enthusiast, also on full format cameras, free handed and with af. A dragonfly Exuvia (remains of the larva after the adult emerged). Nikon D610, Sigma 100-400 (at 210mm), Canon 500D close up lens , and an ant on the left. Blue Chaser (Libellula fulva) Sigma 100-400 (at 210mm), Nikon D610, Canon 500D close up lens. Hand held. Crop 100% of the image above , again you can see the elements of the compound eye . In these photos focus was set to infinity (actual distance from the front element was 50cm) , by focusing at closer distances it becomes possible to get into the range of true macro, especially at 250-300mm. It is advisable however to stay at infinity because the more you get close the harder it becomes to manage depth of field, vibrations and the like. The same problems occur if you zoom beyond 300mm. Anyway, let me repeat it: the combo made by this zoom plus a moderate achromat close-up lens is stunning. Even of a full format body. In conclusion. For close up photography, the zoom on a full format (Nikon:Fx) camera body allows to obtain satisfactory results with flowers and small mammals, while it shows some limitations for smaller subjects. On a APS-C (nikon:Dx) instead it is very good also for dragonflies , butterflies and other not too small critters. Alternatively it can be coupled with an unobtrusive good quality close up lens (same size of a filter) to obtain an extremely versatile kit for close-up, but I would say for nature photography in general, no matter what is the size of the camera sensor. Thanks to Mauro Maratta for the loan of the lens for the test (even if it make me want one!) Thanks to Mtrading, the Italian dealer of Sigma products, for kindly making the lens available for testing by Nikonland staff.