HD Pentax-DA 16-85mm F3.5-5.6

Vignetting

Vignetting, or darkening of corners, occurs due to a lens's imperfect coverage of whole sensor area.  In order to test the vignetting of the 16-85mm, we took a series of photos of an evenly-lit surface across various apertures and focal lengths.

Test Images

Click on any image in the table below for a larger version.  Cycle through the enlarged images to view the change in exposure as you stop down.

	16mm		24mm
F3.5		F4
F4		F4.5
F4.5		F5.6
F5.6		F6.7
F6.7		F8
	35mm		50mm
F4.5		F4.5
F5.6		F5.6
F6.7		F6.7
F8		F8
F9.5		F9.5
	85mm
F5.6
F6.7
F8
F9.5

These results show that vignetting is minimal except at 16mm, where there is a fair amount of falloff until the lens is stopped down to F5.6 or smaller.

Sample Photos

The two photos below illustrate the practical impact of vignetting, which is minimal.  In-camera corrections effectively eliminate it when desired, though it often won't even be discernible unless the original image is underexposed.

16mm F3.5

85mm F5.6

Verdict

The Pentax 16-85mm controls its vignetting very effectively and its consistent performance sets it apart from consumer zooms such as the 18-55mm kit lens or 18-135mm WR.  In practice, the 16-85mm's vignetting is significant only at 16mm at F3.5, F4, and F4.5, with a worst-case corner light loss of about 1.5 stops.  At other focal lengths, even wide-open, you will only observe minor traces of falloff which should not affect images that are properly exposed.

Stopping down by 1.5 stops at 16mm or 0.5 stops at other focal lengths will make vignetting negligible, but even at wider apertures, the vignetting is correctable in-camera or in post with no significant loss in detail.

At identical apertures, the Pentax 16-85mm performs very similarly to the Sigma 17-70mm F2.8-4 "C".