Tamron AF SP 90mm f/2.8 Di VC USD Macro (EOS) - APS-C Format Review - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

Typical for most macro lenses the level of distortion is pretty much negligible and nothing to worry about.

Vignetting

Full format lenses have a natural sweet spot advantage when used on APS-C cameras. Compared to the native full format scope the vignetting is therefore substantially reduced. At f/2.8 you can spot just a bit of light falloff in critical scenes but not to a worrisome degree. The vignetting is already gone from f/4 onward.

MTF (resolution)

Typical for most macro lenses, the Tamron is a great performer in the APS-C scope. The center quality is already very good at f/2.8 and outer image region is also very sharp. Stopping down to f/4 to f/8 lifts the quality to outstanding results. Diffraction effects reduce the quality somewhat at f/11 and more so at f/16 but the quality remains fine here. f/22 should be avoided though.

The centering quality of the tested sample was good. Field curvature is not an issue to worry about.

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 reasonably well controlled for a prime lens with an average width of around 1px at the image borders.

Bokeh

The bokeh (the quality of the out-of-focus blur) is a primary aspect for a macro lens. Surprisingly the Tamron lens shows a certain weakness here.

Out-of-focus highlights have a slightly uneven inner zone but there's just slight outlining effect at the highlight borders.

The general blur in the focus transition zone is very smooth and buttery in the image foreground whereas the image background can be somewhat busy.

Please note that this is reflects the behavior just around the focus point. You can, of course, achieve a very pronounced blur especially in macro scenes with their very shallow depth-of-field.

Bokeh Fringing

Bokeh Fringing is a common issue with relatively fast glass. As you may notice below the out-of-focus halos have different colors - magenta (red + blue) in front of the focus point and green beyond. Unlike lateral CAs, bokeh fringing cannot be fixed easily in post processing. Super-apochromatic lenses don't show LoCAs but these lenses are very rare.

Typical for most fast primes, the Tamron shows some amount of bokeh fringing at large aperture settings which can be reduced by stopping down. However, the issue is mostly gone from f/4 onward.

In addition, these shots also illustrate that there is no focus shift when stopping down.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/2.8 f/4 f/5.6




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