HD Pentax-D FA 100mm F2.8 ED AW Macro

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 HD D FA 100mm Macro 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 HD D FA 100mm Macro, comparing with the SMC version of the lens.

The first observation, which doesn't come as a surprise, is that both the HD and SMC versions show essentially identical vignetting values. Our HD sample is always a tiny bit worse than our SMC sample, but the differences probably amount to our measurement errors.

The second observation is that vignetting is well controlled in all cases. It is of course stronger wide open and on full frame, but anything below 1 EV is hard to spot in most scenes. In other words, vignetting will be a non-issue except at F2.8 on full frame.

Results are particularly good on APS-C, with vignetting reaching nearly zero at F5.6.

The next images show the vignetting for the HD version, at various apertures for both sensor sizes. Click on any thumbnail to compare the vignetting at the given aperture. As stated above, the SMC lens' test images are practically identical.

	Full frame	APS-C
F2.8
F4
F5.6
F8

Verdict

Vignetting figures are excellent for both APS-C and full frame sensors. It reaches 1 EV only at F2.8 and quickly drops to irrelevant levels at smaller apertures. On APS-C, it is a non-issue even wide open.