Tamron SP 85mm f/1.8 Di VC USD - Review / Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

Typical for most tele prime lenses, the Tamron SP 85mm f/1.8 Di VC USD produces marginal distortions of 0.57% (pincushion style).

Vignetting

The vignetting characteristic is about average for such a lens. Thus there’s some substantial light falloff at fully open aperture (1.9EV). Stopping down to f/2.2 reduces the issue and the vignetting is pretty much gone from f/2.8 onward.

MTF (resolution) on the EOS 5Ds R (at 50 megapixels)

The Tamron lens is capable of delivering very sharp results even on a high megapixel camera. The broader center quality is very good straight at f/1.8. The borders/corners are easily good here. Stopping down to f/2.2 increases the quality to an excellent center and a very good outer image region. The peak quality is reached around f/4. The center zone is outstanding at this setting closely followed by the borders and even the extreme corners are very good. Diffraction has, as usual, a higher impact from f/11 onward.

The centering quality of the tested sample was Okay. The field curvature is low.

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

MTF (resolution) on the EOS 5D II (at 21 megapixels)

For the sake of comparison with our legacy tests, we are supplying the MTFs taken at 21 megapixels below. As you can easily conclude, the figures are nothing short of stunning especially when stopping down a little.

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)

Lateral CAs are very low with an average CA pixel width around the 0.6px mark across the aperture range.

Bokeh

Sharpness is one thing but you really invest in such a lens for its bokeh capabilities (out-of-focus rendering).

Let's have a look at the quality of out of focus highlights first. In the image center, the highlights are slightly uneven with just a hint of outlining at the borders. However, the zone where the highlights sustain a circular shape at f/1.8 is rather small. The sample crop below was taken midfield and you can spot that the circular shape isn't really perfect here already. You may also spot a little purple fringing near the very bright spot at the bottom.

Interestingly this results in an almost swirly effect when spreading highlights all over the image field. As usual stopping down restores a more circular highlight shape.

As far as the general blur is concerned, it's smooth in the image background (to the left below) but not all that great in the foreground with some hard edge rendition combined with smearing.

Bokeh Fringing

Sorry, not this time. However, you can spot in the sample images that the Tamron isn't unusual in this respect (reads: it has its share of axial CAs).