Some bokeh and flare test-shots from a Sigma 28mm 1:1.8 II Aspherical (Manual Focus) lens for Pentax KA mount on a Pentax 10MP APS-C sensor.
This lens has a very fast maximum aperture of f/1.8. On the Pentax bodies, the aperture actual registers as f/1.7. The 7-blade diaphragm produces very soft and pleasing bokeh (out-of-focus areas) at the wider apertures.
The bokeh sequence shows the change in the out-of-focus background at f/1.8(f/1.7), f/2.0, f/2.8, f/0, f/8.0.
The flare sequence shows first quite a bit of flare without a lens-hood and then next much-reduced flare with a deep lens-hood (from an 80mm film lens).
© David Anthony