Tamron AF 18-270mm f/3.5-6.3 Di II LD [IF] Asph. VC macro - Review / Test Report - Analysis
Lens Reviews -
Canon EOS (APS-C)
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Typical for extreme range zooms the Tamron exhibits a fairly hefty amount of barrel distortion at 18mm (~3.9%). However, beyond the wide end the problem is actually very well controlled with only slight to moderate barrel (24mm) and pincushion (50mm+) distortion.
The Tamron is a dedicated APS-C lens but despite the ambitious design vignetting is comparatively well controlled except at 18mm @ f/3.5 (~1EV) and the very long end @ f/5.6 & f/6.3 (~0.8EV). In critical situation it already helps to stop down a little (just a stop).
The predecessor of the 18-270mm VC, the 18-250mm, came up with surprisingly high resolution numbers in the MTF lab but these tests were based on an 8mp (Canon) and 10mp (Nikon) test bodies. The situation is a little different now (@ 15mp) and the 18-270mm VC struggled somewhat to impress here. At 18mm the lens is able to deliver a generally decent quality with an extremely sharp center and acceptable borders. At 24mm you should avoid the max. aperture setting because of very soft borders (sharp center) but the quality catches up at medium apertures. This pattern repeats at 50mm (best setting) and 100mm. At 200mm and 270mm we still have a fairly decent center performance but the border quality deteriorates further, especially at 270mm where it takes f/11 to reach acceptable resolution figures here.
The (focus-)field curvature is very low. The centering quality of the tested sample was generally good but it deteriorated somewhat at and beyond 200mm (not unusual for lenses with image stabilization). In the field it also became obvious that the contrast level is also somewhat reduced throughout most of the range.
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
Chromatic Aberrations (CAs)
In the lower part of the zoom range the lateral CAs (color shadows at harsh contrast transitions) are relatively well controlled (@ 15mp) with an average pixel width up to 2px at the image borders. However, at 200mm and more so 270mm the problem gets very pronounced (~3px) and the CA distribution is no longer symmetrical at this setting (peaking beyond 4px in one corner).