Sigma AF 70-200mm f/2.8 EX OS HSM (FX) - Review / Test Report - Analysis
Lens Reviews - Nikon / Nikkor (full format)

Distortion

The lens shows distortion characteristics that are typical for this lens class. At the short end there is a slight amount of barrel distortion which flips over to around 0.9% pincushion distortion at 135 mm and just above 1.5% at 200 mm.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
70mm 135mm 200mm

The chart above has a real-world size of about 120x80cm.

Vignetting

The lens shows very similar vignetting characteristics at all tested focal lengths. Wide open, the light fall-off reaches almost 1.5 EV at the image corners. Stopping down reduces the issue considerably and from f/5.6 onwards vignetting should no longer be an issue for most subjects.

We're performing our vignetting analysis based on (uncorrected) JPEGs straight from the camera. The JPG engine of the Nikon D3x features a rather flat gradation curve, thus has a moderate contrast characteristic, resulting in comparatively low vignetting figures - the corresponding Canon figures are roughly 40% higher due to the more aggressive default contrast setting.

MTF (resolution)

At all focal length settings the image center delivers very good resolution wide open, which increases to excellent sharpness when stopped down.

At 70mm the borders show very good resolution wide open and even increase to excellent figures at f/5.6. The image corners follow only slightly behind, with good sharpness wide open and very good figures stopped down. The performance peak across the frame is reached at f/8 here.

At 135mm, the situation is very similar, except for the border resolution, which no longer reaches excellent figures stopped down.

At the longest focal length setting, the borders and corners show significantly less resolution at large apertures. Wide open, the results are just fair here. Both regions recover by stopping down, but the lens needs to be set to f/8 to reach very good resolution here.

At the long end of the zoom range, the lens shows a small amount of focus shift when stopping down (residual spherical aberration).

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Chromatic aberrations (color shadows at harsh contrast transitions) are generally well controlled. The largest amount of CAs is visible at 135mm wide open with an amount of 1.55 pixels at the image borders.

Please note that lateral CAs can easily be corrected in software or by the camera itself (most modern Nikon DSLRs remove CAs on-the-fly if you shoot JPGs).

Bokeh

Being a fast tele lens one of the lens' welcome abilities is to separate the main subject from the background, so rendering of out of focus areas is an important aspect.

The EX 70-200 OS delivers a generally very smooth bokeh at all focal lengths.

Thanks to 9 rounded aperture blades, background highlights remain circular throughout the whole aperture and focal range, except at the image borders where they are cut off due to mechanical vignetting. They show a smooth filling with almost no outlining.

Bokeh Fringing

Bokeh fringing is a common issue with relatively fast glass. It's visible as halos of different colors in out-of-focus areas - magenta (red + blue) in front of the focus point and green beyond.

The EX 70-200/2.8 OS is an APO lens. Consequently, there is only a very small amount of bokeh fringing wide open, which is completely gone by f/4 and beyond.

The images below, shot at 200mm, illustrate the focus shift when stopping down, as mentioned in the MTF section.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/2.8 f/4.0 f/5.6 f/8.0 f/11.0




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