For this distortion test, we found an evenly lit interesting brick wall that had regularly spaced joints. With the camera on a tripod, parallel and level with the brick wall, a series of shots were taken. We wanted to see how well the lenses were designed to eliminate distortion. Below are sample pictures taken with the Pentax DA 50mm F1.8, FA 50mm F1.4 and the D FA 50mm F2.8.
We are happy to report that none of the Pentax 50mm lenses had any measurable distortion. If the lenses had barrel distortion it would have cause the lines to curve or bulge out ward. If they had pincushion distortion it would have caused the lines to curve inward.