Pentax SMC DA* 300mm f/4 ED [IF] SDM - Review / Test Report - Analysis
Lens Reviews - Pentax

Distortion

Typical for a medium tele fix-focal lens the level of distortion is negligible and nothing to worry about in in practical terms.

Vignetting

There's only a minimal amount of light falloff at f/4 which supports the rumor that it's actually a full format lens. Beyond the max. aperture the vignetting is absolutely negligible.

MTF (resolution)

The Pentax lens produced very decent resolution figures in the MTF lab. It delivers a very good center-to-edge resolution straight from f/4. The only marginally higher peak resolution is reached at f/5.6. Diffraction effects reduce the quality from f/8 onwards but the quality remains very usable even at f/11.

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 generally well controlled at around 0.6px at the image borders and usually nothing to worry about.

Bokeh Fringing

Bokeh fringing shows up as magenta colored halos in front the focus point and green beyond. The Pentax lens shows only a slight amount at f/4 and the issue is largely reduced at f/5.6 and gone by f/8.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/4 f/5.6 f/8

Bokeh

The bokeh (the quality of the out-of-focus blur) is a major aspect for all tele lenses because it is often an essential part of a scene. The Pentax DA* lens does a pretty good job here in general. The out-of-focus highlights are perfectly circular and the inner zone is quite uniform at f/4. However, there's a pronounced outlining effect at this setting. The circular shape deteriorates a little from f/5.6 onwards but the outlining effect dissolves.

The general quality blur is very smooth in the foreground (left sample crop below) and just a little more nervous in the image background (to the right).




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