[the following is a modified repost from Myrmecos]

A reader asks:

I also have a MP-E lens with the MT-24EX flash unit. I was curious to know something I didn’t see you mention in your recent blog post about this setup.

Could you share any technical points regarding how you achieve the visible backgrounds with that lens? In general, I get very nice shots with everything beyond the focused subject completely blacked out.

Since dark areas in photographs are the bits that aren't sending light to the camera, it follows that getting a visible backdrop means applying light behind the subject.

Earlier, I wrote that the black backdrop in macrophotography with flash is a sort of default setting. When bright flash is applied to a subject in the foreground, the background will fade to black as a matter of course. Consider this shot of acacia ants taken in a Panamanian forest:

Although I snapped this picture during the day, the photo is mostly black. That's because little ambient light penetrated the small aperture I used to gain depth-of-field. Nearly all the light comes from the flash.

To bring up the background requires increasing the ISO to pick up more ambient light (=more noise), opening the aperture (=less depth of field), decreasing the shutter speed (=more motion blur), adding a second flash aimed behind the ants (=more work), or positioning something close enough behind the subject so as to reflect some of the foreground flash. In this case, I followed the latter strategy and rigged a solution in the field:

With a colorful leaf arranged a few inches behind the ants' thorn and catching the flash, the resulting photographs have a different tone:

I was lucky that the thorny undergrowth provided an easy way to suspend a leaf. Paper clips are more reliable, and it's a good idea to carry a few in the field. In any case, the principle is the same: put something close enough behind the subject to reflect the flash.