Pentax SMC-FA 100mm f/2.8 macro - Review / Lab Test Report - Analysis
Lens Reviews - Pentax
Article Index
Introduction
Analysis

Distortion

Macro lenses are designed to produce minimal distortion and the Pentax SMC FA 100mm f/2.8 macro does certainly qualify here (0.02%).

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

Vignetting

As a full format lens the FA 100mm f/2.8 enjoys a sweet spot advantage on the K10D. At f/2.8 the problem is slightly more pronounced but even here the level of vignetting shouldn't be really field-relevant. From f/5.6 the problem is hardly detectable anymore.

MTF (resolution)

The FA 100mm f/2.8 macro produced very high resolution figures in the MTF lab. The resolution is already very good and exceptionally even at f/2.8. Stopping down does only result in a marginal improvement although a slight peak is reached at f/8 with an excellent center to border quality (just). Beyond f/8 the lens runs into the usual and unavoidable diffraction problems. At f/22 the resolution is still amazingly high - actually too high in relation to the diffraction problems at this setting. The nominial aperture (f/22) is probably larger than the effective one. At f/32 there's only the typical image soup left.

The contrast level of the FA 100mm f/2.8 macro seems a bit lower compared to other lenses in this lens class.

Please note that this test has been performed at a conventional working distance (~6m). Dedicated macro tests are NOT possible at this stage!

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 low and generally not field relevant at all tested settings.

Verdict

The Pentax SMC-FA 100mm f/2.8 macro is an very good lens without significant weaknesses. The resolution level is very high (although not exceedingly so) from f/2.8 all the way down to f/22 (nominal, the effective aperture is probably larger). Distortions are absent and CAs are not field-relevant. Same goes for vignetting. Thanks to a metal body and tight tolerances the build quality of this old lens is excellent.

Optical Quality:
Mechanical Quality:
Price/Performance:discontinued



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