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Tamron AF 24-135mm f/3.5-5.6 SP AD Aspherical (IF) - Review / Lab Test Report - Analysis |
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Lens Reviews -
Canon EOS (APS-C)
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Page 2 of 2
Distortion
The lens shows a medium degree of barrel distortion at 24mm changing to moderate pincushion
distortion towards the long end of the zoom range. The neutral settings should be a little
below 40mm. Not all that bad for a 5.6x zoom ratio.
24mm:
40mm:
75mm:
135mm:
The chart above has a real-world size of about 120x80cm or 40x the focal length.
Expect more distortion towards closer focus distances.
Vignetting
Typical for full format lenses on APS-C DSLRs vignetting is no significant issue thanks to
taking advantage of the inner portion of the projected image circle. Nonetheless the
very low degree of vignetting even at wide-open aperture is a little surprising. A seldom
event actually.
MTF (resolution)
In the lab the lens showed decent resolution characteristic throughout the tested zoom
range but the sweet spot is clearly located towards the wide end of the zoom range. At 24mm
and 40mm the center quality is very good at wide-open aperture and even excellent
at medium apertures. The borders follow somewhat behind in quality but they're already
good enough at wide-open aperture increasing to very good figures at f/8.
The performance penalty at 75mm is still quite marginal whereas there's a significant
drop at 135mm @ f/5.6 where both the center as well as the border quality is just good.
Visually the lens also suffers from lower contrast here. Nonetheless the lens is still
capable to lift up the resolution to very good figures at f/8 and f/11.
Please note that the MTF results are not directly comparable across the different systems!
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 very pronounced
at 40mm and even more so at 24mm with an average pixel width in the 1 to 1.5 pixels range.
Towards the long end the issue is marginal.
Verdict
The Tamron AF 24-135mm f/3.5-5.6 SP AD Aspherical (IF) is indeed a worthy competitor
for the Canon EF 28-135mm f/3.5-5.6 USM IS. The resolution and vignetting figures are slightly
superior whereas it's a tie regarding distortions. The Tamron shows a rather weak CA characteristic
though. The build quality of the lens is very decent but it leaves a little to be desired
regarding AF speed. Due to the 1.6x cropping factor on APS-C DSLRs the range isn't all that
attractive than it used to be so shopping for a new ones seems rather pointless regarding
the existing alternatives. However, on the long term Canon users may see mainstream
full frame DSLRs where the lens could show its old qualities again.
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