Vignetting by definition is a reduction of an image’s brightness compared to the image center. For this vignetting test we took a series of pictures of a grey board and looked for an even spread of grey across the image. The other factor that effects the lens vignetting is the F stop. As the lens is stopped down, it will reduce the effects of the optical vignetting. Problems exist when one or more of the corners are significantly darker than the center. Below are sample pictures taken with the Pentax DA 50mm F1.8, FA 50mm F1.4 and the D FA 50mm F2.8.
Surprisingly, none of the Pentax 50mm lenses had any measurable vignetting. It would be unusual if the FA 50mm F1.4 and the D FA 50mm F2.8 lenses had vignetting since they are designed for full frame use and the APC-S sensor is smaller. Interestingly, we did not see any evidence of vignetting with the DA 50mm F1.8, either. We thought that perhaps since it is designed for the APS-C digital format, we might get some darkening in the corners, but none was present.