HD Pentax-DA* 16-50mm F2.8 ED PLM AW

Vignetting

In simple terms, vignetting is the darkening of the corners of an image that occurs at wider apertures. Every lens, wide open, will exhibit some. Most of the time, it need not be a problem for modern photographers. First, it is always possible to shoot at smaller apertures, mitigating the effect. Second, cameras released in the last few years often have built-in tools to remove vignetting in a way that's invisible to the user. Advanced software also often incorporates lens profiles which can seamlessly correct vignetting. Last, it is always possible to purchase higher-quality lenses that will show milder vignetting.

A fast lens is somewhat more likely to show vignetting than a slow one, although this is not a hard rule. A full frame lens also benefits from a sweet spot on APS-C, but shows its flaws more visibly on full frame cameras. A zoom is more likely to show vignetting at its wider focal lengths.

This section presents how the DA* 16-50mm PLM performs in regards to vignetting.

Vignetting Test

The test was performed by pointing the lens at a blank wall. In-camera correction was de-activated; results with lens correction active will be significantly better. Resulting files were scaled down, converted to grayscale for improved visibility, then exported. The following settings were used:

The following chart summarizes the findings with the DA* 16-50mm PLM.

One of the takeaways of the graph above is that there is an important decrease in vignetting at 30mm. 16mm and 50mm are essentially similar. 

The scale of this graph can be misleading, because even at wider apertures, the lens shows low vignetting values. Generally speaking, values below 1 EV will have little effect in real life, and the lens never produces more than 0.8 EV. Results at 50mm are astounding, with extremely low values even wide open.

Vignetting is easy to correct via post-processing, but corrections are never without cost, and it's generally better to start with a good images. The 16-50mm PLM exceeds expectations in this regard.

The next images show the vignetting at various apertures. Click on any thumbnail to compare the vignetting at the given focal length.

	16mm	30mm	50mm
F2.8
F4
F5.6
F8

Verdict

Vignetting figures are outstanding. At 30mm, there is no vignetting to speak of. At the other focal lengths there is some vignetting but below 1 EV, it is hard to notice in real life.