5) Lens Sharpness and Contrast
As I have pointed out before, the Sigma 120-300mm f/2.8 DG OS HSM is identical to its predecessor optically. I had both versions of the lens for testing and after a couple of tests at different focal lengths, I was able to confirm that both produced about the same Imatest figures. There was a very slight variance in performance (less than 3% delta), which shows that Sigma has been doing a much better job in terms of quality assurance. The older EX version had a slight back focus issue, but it was not a big deal, as I was able to correct it with AF Fine Tune (see my article on lens calibration). The nice thing about the new 120-300mm, is that you can fine tune it with the USB dock without having to do it in your camera.
So how did the Sigma 120-300mm f/2.8 DG OS HSM perform optically? Let’s take a look at some Imatest charts from different focal lengths:
At 120mm, the lens is at its weakest spot in terms of sharpness. The wide open performance at f/2.8 is below average and the corners are quite weak. Stopping down to f/4 improves the sharpness greatly and stopping down to f/5.6 yields maximum performance for the center and the mid-frame. The corners are the best at f/8 and diffraction kicks in at f/11 on the D800E, resulting in decreased performance at smaller apertures.
The performance of the lens improves as you zoom in. At 150mm, the lens is better optically than at 120mm throughout the frame. Performance at f/2.8 is still rather weak, but gets very strong at f/5.6, reaching very high resolution figures.
And it gets even better at 200mm, with excellent resolution figures at f/5.6 and increased mid-frame performance. The corners are a little weaker though.
At the longest end of the zoom range, the performance of the lens drops a little at large apertures, but picks up again at f/5.6. The corners suffer even more at the longest end, reaching acceptable levels only at f/8.
Overall, the Sigma 120-300mm f/2.8 seems to be a good performer when stopped down. Unfortunately, its performance is not very impressive wide open, especially in the corners. The sweet spot of the lens seems to be at f/5.6 at all focal lengths.
Contrast-wise, the Sigma 120-300mm f/2.8 is excellent. Just make sure to keep that long lens hood on at all times, since contract might decrease greatly when sun rays reach the front lens element. The lens renders colors beautifully, so no complaints there either.
6) Sigma 120-300mm f/2.8 Performance with Sigma 1.4x Teleconverter
One of my personal annoyances with third party lenses, is the fact that they cannot work well with Nikon teleconverters. In the case of the Sigma 120-300mm f/2.8 DG OS HSM, none of the Nikon TCs would even mount on the lens. In order to test the lens thoroughly, I had to get both the 1.4x and the 2.0x Sigma teleconverters. Since teleconverters are used to extend the focal length of lenses, I only tested the Sigma 120-300mm at the longest end of the range (the lens becomes a 168-420mm f/4 lens with the 1.4x TC). Let’s take a look at how the lens performs with the 1.4x Sigma teleconverter:
As you can see, there is definitely a visible drop in sharpness across the frame. Once again, the wide open performance of the lens at f/4 is rather weak, with f/5.6 producing the best sharpness in the center and mid-frame. Corners peak at f/8 and diffraction kicks in at f/11.
If you would like to find out more about the performance of this teleconverter, check out my Sigma 1.4x teleconverter review.
7) Sigma 120-300mm f/2.8 Performance with Sigma 2.0x Teleconverter
The Sigma 2.0x teleconverter extends the range of the lens to 600mm, making it a versatile 240-600mm f/5.6 lens. Let’s take a look at how the lens performed optically with the longest available teleconverter from Sigma at 600mm:
As expected, there is a rather significant drop in sharpness with the 2x teleconverter. The wide open performance at f/5.6 is very weak and the lens should be stopped down to f/8 to get good center performance. As I have noted earlier though, the lens can actually acquire focus with the 2x teleconverter even in low light situations (tested on the Nikon D3s camera body), which can be useful for situations when you need the maximum reach and working AF. Keep in mind that autofocus accuracy surely suffers and there is a visible drop in contrast though, which is again expected from a 2x teleconverter.
If you would like to find out more about the performance of this teleconverter, check out my Sigma 2.0x teleconverter review.
One of the strengths of long telephoto lenses is the beautiful, creamy bokeh they are able to produce. On top of that, due to the shallow depth of field, subjects can be isolated very effectively, resulting in very smooth backgrounds. Thanks to the wide maximum aperture of f/2.8, the Sigma 120-300mm f/2.8 is capable of producing very good to excellent bokeh. Sure, critical sharpness might not be there, but if you want a great looking bokeh and you are ready to compromise on sharpness a little, then set the lens to f/2.8 and shoot away. And when you need more depth of field for close subjects, stop the lens down to f/4 and you will still get beautiful background highlights.
9) Vignetting / Light Falloff
The Sigma 120-300mm f/2.8 DG OS HSM shows some vignetting at f/2.8 at all focal lengths. Stopping down to f/4 improves vignetting quite a bit and f/5.6 brings it down to very low levels. Looks like vignetting is at its worst at the longest end of the zoom range. Take a look at the following chart that summarizes my findings:
And here is the visualization of the worst case scenario at 300mm:
10) Ghosting and Flare
The large and long hood on the Sigma 120-300mm f/2.8 is there for a reason. Most long-range telephoto lenses, including this one, do not perform well when shot against a bright light source. So, if you shoot against the sun, you might get some large, nasty flares and plenty of ghosting, which is quite normal. In addition, a bright source of light will surely decrease the contrast of the lens as well, so keep that in mind.
Distortion is practically non-existent at the shortest end of the range, but picks up as you zoom in, in the form of pincushion distortion. It is at its strongest level at 300mm, at around 1.13%. Distortion is generally not a problem, because it can be easily fixed in Photoshop or Lightroom using the Lens Corrections module.
12) Image / Optical Stabilization
When it comes to optical stabilization, the Sigma 120-300mm f/2.8 once again shares exactly the same stabilization system as the one found on its predecessor. According to Sigma, there should be 4 stops of shutter speed compensation, similar to what Nikon claims for its Vibration Reduction II (VR II) system. The Sigma 120-300mm performed quite well with OS turned on and while I cannot say that I was able to get sharp images at 4 stops less than the focal length of the lens, it was still pretty good at around 3 stops. In terms of keepers, I would say the lens yields comparable results to Nikkor lenses with stabilization, so it is a pretty solid system in my opinion.
Sigma comes with two modes for optical stabilization – Mode 1 for normal shooting and Mode 2 for panning. I did not play much with the panning mode, although some might find it useful for shots involving motion. Another cool feature of the 120-300mm, is the fact that you can actually customize viewfinder view modes for optical stabilization using the USB dock. There are three modes to choose from: Dynamic View Mode, Standard and Moderate View Mode. These modes allow you to fine-tune the way stabilization impacts what you see in the viewfinder.
Let’s now move on to the good stuff – Comparisons to other super telephoto lenses.