Thank you, folks.
John, this one was taken with my Canon 5D and 100mm f/2.8 macro lens. However, the Olympus E-M1 plus 60mm (120mm equivalent) f/2.8 macro lens achieves 1:1 magnification at a focus distance of about 19 cm, whereas the corresponding distance for the Canon setup is about 31 cm. So at their minimum focusing distances, their depths of field are not that different. Of course, the shorter working distance makes the Olympus's use with skittish critters rather more problematic.