I chose Pentax for the small system so after comparing this lens with the Sigma 105mm EX MACRO I decided to go with the Pentax. Very small and light (345 grams) compared to other marques. Tack sharp from f/4 - f/11 and still very good wide open at f/2.8.Virtually no distortion, vignetting or chromatic abberations. Excellent colour, very neutral and bokeh is creamy smooth.
Clamp locks focus to allow 'Back and forth' manual focusing technique. AF is slow and noisy, this is par for the course with macro lenses but the lack of a focus limiter is unforgivable as it results in severe hunting. Not as well built as the considerably heavier and larger Sigma 105mm MACRO. One of my favourite lenses with clear and vibrant results I can rely on.