the degree of bokeh, or OOF background, is to some degree dependent on the sensor size, in addition to aperture. large sensors make it easy to blur the background into a smooth palette at wide apertures, while small sensors, even with the lens wide open, don't offer the same degree of blur. that's why portrait and wedding photographers really like full-frame bodies... for shots like your DIF images, the softer and smoother the background, the greater the contrast with the sharp, clear dragonfly. i can see why you didn't want a "busy" backdrop for these... the clutter would very definitely detract from the image.
