Tamron AF 70-300mm f/4-5.6 LD Di macro (Pentax K) - Review / Lab Test Report - Analysis
Lens Reviews - Pentax
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Introduction
Analysis

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Distortion

The Tamron exhibits a negligible degree of barrel distortion at 70mm changing to slight pincushion distortion at 200mm and 300mm. This shouldn't be overly field relevant.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
70mm 200mm 300mm

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

Vignetting

Used on the K10D the (full format) Tamron shows only a slight degree of vignetting at wide-open aperture (<0.5EV). This is usually nothing to worry about within the APS-C scope.

MTF (resolution)

The resolution characteristic of the Tamron is not exceptionally high but generally still decent. At 70mm and 200mm the center and border performance is on a very good level straight from wide-open aperture down to f/11. At 300mm there's the expected drop in quality. The center remains on a very good level whereas the borders are somewhat soft at f/5.6. Stopping down lifts the border quality to quite respectable levels. At 200mm and 300mm the contrast is a bit dull at large apertures - this is typical for tele zoom lenses in this class.

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)

Lateral Chromatic aberrations (color shadows at harsh contrast transitions) are relatively moderate at 70mm but quite pronounced at 200mm and 300mm.

Here's an example at 300mm f/8 (upper left and right border):

Verdict

Regarding its extremely low price tag you can't really expect a stellar performance from the Tamron AF 70-300mm f/4-5.6 LD Di macro but from a value perspective it is fairly amazing what it can give you. The resolution is very good till 200mm. At 300mm there's a drop in quality especially at f/5.6. Typical for such lenses the contrast suffers at wide-open aperture so stopping down is advisable from about 200mm onwards. Distortions and vignetting are not field relevant whereas lateral CAs (color shadows at the image borders) can be fairly obvious at longer focal lengths. Apart from the rotating front element the build quality of the lens is actually pretty fine for a lens in this class (better than e.g. the Canon EF 90-300mm f/4.5-5.6 or Nikkor AF 70-300mm f/4-5.6D ED).

Optical Quality:
Mechanical Quality:
Price/Performance:

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