Backlit mayfly spinner

Frontlit mayfly spinner

The use of extension tubes allows for greater "magnification" but greatly reduces the depth of field essentially making the focus plane extremly narrow.  On a full frame sensor like the Nikon D3S, using extension tubes also causes some vignetting--darkening of the corners.  These images were taken handheld using an iso of 1,600 in order to get a shutter speed fast enough and an aperture around f10 for a reasonable level of depth of field.  On cold mornings mayflies and bugs in general are far more still and much easier to capture...

Camera: Nikon D3S

Lens: Nikon Micro 105 with extension tubes