Pentax-DA 10-17mm F3.5-4.5 Fish-eye
Vignetting
Vignetting is the decrease of brightness (or shading) in the corners or periphery of an image. To test the SMC Pentax-DA 10-17mm F3.5-4.5 Fish-Eye ED [IF] for vignetting, we took shots of the sky at various focal lengths and at the widest to mid-range apertures.
10mm | 12mm | |
| f/3.5 |  | N/A |
| f/4.0 |  |  |
| f/5.6 |  |  |
| f/8.0 |  |  |
14mm | 17mm | |
| f/4.0 - f/.4.5 |  |  |
| f/5.6 |  | |
| f/8.0 |  |  |
To provide a better quantification of the vignetting of this lens, we compared the average pixel value of the corners against the center, after converting the image to monochrome. The resulting corner-to-center average pixel value ratios (expressed as percents) are the following:
10mm | 12mm | 14mm | 17mm | |
| f/3.5 | 64.84% | - | - | - |
| f/4.0 | 65.12% | 73.91% | 68.72% | - |
| f/4.5 | - | - | - | 73.45% |
| f/5.6 | 78.89% | 83.25% | 75.48% | 80.18% |
| f/8.0 | 84.23% | 86.98% | 81.66% | 85.55% |
Verdict
Upon observation of the above ratios, we can conclude that the vignetting of the DA 10-17mm Fish-eye, while not terrible, is certainly worse than what we'd expect from a quality lens. Assuming a guideline of 1 stop of light loss as the acceptable threshold, this lens is well within the acceptable range with a maximum light loss of 2/3 stops, but not below the ideal of threshold of below half a stop.
To be fair, in the typical application of this lens, it is very unlikely that the user would be photographing 100 to 180 degress of a uniformly-lit scene. In this regard, although the vignetting of the DA 10-17mm Fish-eye is worse than we had expected, but its effect on the image will be much less visible that the numbers would otherwise indicate.
