13) Compared to Nikon 300mm f/2.8G VR II
Let’s see how the lens compares optically to the superb Nikon 300mm f/2.8G VR II at 300mm:
The Nikon 300mm f/2.8G VR II is an insanely sharp lens. There is simply no comparison between the two, especially at the maximum aperture of f/2.8. Even the corners of the Nikon 300mm f/2.8 look better than the center of the Sigma 120-300mm. Stopped down to f/5.6, the Sigma 120-300mm gets very close in the center, but still significantly worse everywhere else.
Now let’s take a look at how both lenses perform at 420mm (with 1.4x teleconverters):
Once again, the Nikon 300mm f/2.8G VR II is clearly superior. Its mid-frame and corner performance is impressive, even with a teleconverter attached. The Sigma 120-300mm f/2.8 gets very close in the center at f/5.6, but it suffers greatly everywhere else.
The last comparison is to take a look at both lenses with a 2x teleconverter. Here is the comparison:
Both lenses suffer quite a bit with 2x teleconverters. However, the Nikon 300mm f/2.8G VR II does quite well in comparison wide open. At f/8, both lenses resolve about the same amount of detail in the center, but the Sigma 120-300mm does much worse in the mid-frame and the corners.
14) Compared to Nikon 200-400mm f/4G VR
I have been shooting with the Nikon 200-400mm f/4G VR for a number of years now. It is a very versatile lens and it works very well with a Nikon 1.4x teleconverter. Let’s take a look at how the two lenses compare optically at 300mm:
My 6+ years old beat up 200-400mm is optically inferior to the Sigma 120-300mm f/2.8 at f/4 and smaller. Its corner performance is pretty good, but the Sigma 120-300mm clearly looks better in the center.
Let’s see what happens when we compare both at 400mm. Obviously, the Sigma 120-300mm cannot reach 400mm, but we can compare its performance at 420mm, with the 1.4x Sigma extender:
The sharpness difference here is pretty clear – the Nikon 200-400mm f/4G VR is much sharper wide open than the Sigma 120-300mm f/2.8. Stopped down, the Sigma 120-300mm gets better, but still cannot get close to what the Nikon is able to resolve across the frame. This basically shows that the Nikon 200-400mm f/4G VR is still a better option for reach than the Sigma. However, at almost twice in price, one has to wonder if it is even worth it. Personally, I would opt for the Nikon 300mm f/2.8G VR II with teleconverters if I wanted to get the best performance at the 400mm range. Obviously, it is not as versatile of a tool for photographing bears in close proximity in Alaska, but it is still a great choice for everything else.