DA* 16-50mm vs. Sigma and Tamron 17-50mm F2.8 Comparison
Image Quality: Sharpness
Methodology
In reviewing these lenses for image quality we attempted to test every relevant aspect of the lenses' performance, including sharpness, vignetting, distortion, bokeh, and flare resistance. For sharpness testing, we used both static chart-based evaluation and field tests, as we feel test charts don't always show off the subjective sharpness of the lens—i.e., the combination of resolving power and contrast that results in perceived sharpness.
Studio Sharpness Tests
For this test, we placed the test camera (a K-5) on a tripod perpendicular to a test chart affixed to a white wall, evenly illuminated by studio lights. We shot each lens at f/2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0, and, in the case of the Tamron, 32.0, and at 16 or 17mm, 35mm, and 50mm.
- Single-point Live View autofocus (on center of chart)
- ISO 100
- JPEG (highest quality)
- White balance set to Auto
- Auto-exposure; Multi-segment / Evaluative metering
- Image mode set to camera default ("Bright")
- Dynamic range extension off; In-camera lens corrections off
- Camera on tripod, 2-second self-timer; SR off (OS off for the Sigma)
Conclusions
In general, we found that the Sigma performed best across the frame, consistently faring better than the Tamron and Pentax lenses in corner and border sharpness. However, we found that the Tamron lens was the sharpest in the center portion of the test image on a similarly consistent basis. The Pentax lens, which was besieged by chromatic aberration that reduced its subjective sharpness at wider apertures, occasionally matched the performance of the other two but rarely outperformed them.
Field Sharpness Tests
For this test, we placed the test camera (a K-5) on a tripod with a view of a distant landscape. We shot each lens at f/2.8, 4.0, 5.6, 8.0, and 11.0, and at 16 or 17mm and 50mm.
- Single-point Live View autofocus (on center of scene)
- ISO 100
- JPEG (highest quality)
- White balance set to Auto
- Auto-exposure; Multi-segment / Evaluative metering
- Image mode set to camera default ("Bright")
- Dynamic range extension off; In-camera lens corrections off
- Camera on tripod, 2-second self-timer; SR off (OS off for the Sigma)
Conclusions
For the most part, the field test images bore out the conclusions gathered from the studio sharpness test. The Sigma lens was once again sharpest in the corners and fell just behind the Tamron in center sharpness. The Pentax lens was once again affected by CA, though in the harsh New Mexico sunlight, all of the lenses displayed this characteristic to some degree. The Tamron seemed to suffer from spherical aberration-induced subjective sharpness loss at f/2.8 (particularly at 50mm), giving it a "glowy" sort of look.
