Macro photography - Part 15: Macro flash and background - pay attention to the background.

Blue tobacco hornworm - Left:  White background.  Right:  No background but with "halo" lighting.

As reproduction ratios increases, depth of field decreases.  As you approach a 1:1 ratio, the depth of field becomes critical.  At f/4, a 1:1 reproduction ratio has less a depth of field less than 0.2 mm.  At f/16, that depth of field increases to about 0.6 mm.  At f/64, about 2.5 mm.  (note:  the apertures given are effective apertures and not actual).

If you are stacking there is less of an issue as lower apertures means the background will be visible but highly blurred.  However, if you shoot at small apertures to maximize depth of field, the background will be pitch black for anything at distance.  This is assuming that you are not shooting with a very high ISO.  To keep from getting the black background, you have to make some changes.

I love using white paper plates; they are bright white, stiff, and readily available.  I put them just behind the subject so that my flash shows them as being white but not blown out.  You can see that on the left image.  If you don't have a close background, as in the right image, you can have another flash illuminating the back side of the subject.  This works the same way as halo lighting for someone's hair and gives the edges a bit of a glow instead of having parts of the subject fade into nothingness.  If you look closely at the caterpillar's back, you will notice a slight shine to the edge.  This helps separate the subject from the black void behind it.

If you are shooting in a natural environment, you can let nature be its own background.  Sometimes I will manipulate leaves or debris behind the subject to prevent the black void from showing up.  Keep in mind that illumination from flash disperses at the square of the distance, so keep the background close to the subject or it will be severely underexposed.  You can see both examples in the images below.

Left:  Honeybee on flower.  Background dark as it is some distance from subject.
Right:  Garden Tiger Moth on wood surface.  Background close to subject so well lit.

Thanks for reading.

Eric Svendsen     www.ericspix.com


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