Tamron AF 14mm f/2.8 SP Aspherical [IF] (Pentax K) - Review / Lab Test Report - Analysis
Lens Reviews - Pentax
Article Index
Introduction
Analysis

Distortion

Ultra-wide lenses are very difficult to correct and a focal length of 14mm is fairly extreme for a full format lens. As such it is not surprising that the Tamron shows a quite significant degree of barrel distortion (2.5%). However, even so this is still better than many ultra-wide zoom lenses.

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

Vignetting

The Tamron AF 14mm f/2.8 SP may be a full format lens but it still suffers from a fairly hefty degree of vignetting (1.4EV @ f/2.8) when used on the K10D - surely a side effect of the comparatively fast max. aperture. The situation is already much better at f/4 and vignetting should be fairly negligible under field conditions from f/5.6 onwards.

Here's an example shot taken @ f/2.8:

MTF (resolution)

The Tamron produced rather mixed resolution results in the lab. The center performance is superb straight from the max. aperture. However, the borders and more so the extreme corners aren't quite as impressive especially at f/2.8 where the word "soft" comes into mind. At f/5.6 the results are very good although not any better than the quality delivered by modern zoom lenses in this range. At f/11 diffraction effects results in the usual decrease of quality. The field curvature is relatively moderate for an ultra-wide lens.

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 chromatic aberrations (color shadows at harsh contrast transitions) are comparatively low at large aperture settings but increase significantly when stopping down. At f/8 to f/11 CAs reach a rather disturbing degree of 1.8-2px on the average at the image borders.

(Note: CAs can be reduced via imaging tools)

Verdict

The Tamron AF 14mm f/2.8 SP Aspherical [IF] is a slightly disappointing performer on the K10D - a fate that it shares with the quite similar Nikkor AF 14mm f/2.8D ED on Nikon DSLRs. It seems as if these fairly old ultra-wide fix-focal lenses aren't the best match for today's DSLRs anymore. The center resolution is nothing short of superb but the border and extreme corner quality, and this is important in this class, is not quite as impressive specifically at large apertures. The level of barrel distortions is quite good for a lens in this class whereas CAs (color shadows) are on the high side. Vignetting is a problem at f/2.8 but fairly well controlled beyond. The build quality is pretty decent. So is the Tamron worth the high price (~1100€/US$) ? The Tamron shines regarding its large max. aperture but quality-wise it doesn't offer anything beyond the mainstream. If you're looking for a "duo-mode" (film + digital) lens the more affordable Sigma AF 12-24mm f/4.5-5.6 EX is at least as good (although slower) and there're a couple of good alternatives among the digital-only ultra-wide lenses.

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