Up close and personal with a varroa mite
Graham Royle, NDB
Macro photography can show objects in huge detail. Typically, subjects are photographed at a magnification of 1:1, which means the subject is as large on the camera’s sensor as it is in real life. With extreme macro, the magnification is even higher.
One of the challenges with macro photography, and extreme macro in particular, is the very narrow depth of field (the short distance between the nearest and the furthest objects that are in focus). The higher the magnification, the smaller the depth of field and therefore the more difficult to get the points of interest in focus. Anyone with experience using microscopes will be familiar with this effect.
When viewing a bee using a stereo microscope, only parts of the bee are in focus. For example, when viewing a bee face-on, if the head is in focus, the abdomen will be blurred. To view the abdomen, the focus must be adjusted. But having brought the abdomen into focus, the head will now be blurred. This can be a minor irritation when using the microscope, but it becomes a very significant issue when wanting to photograph the bee, as it isn’t possible to take a single photograph showing the entire insect in focus.
To overcome this limited the depth of field, a technique called ‘focus stacking’ can be used. Several photographs are taken
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of the subject, adjusting the microscope focus for each shot. The resulting images are processed by focus-stacking soſtware to produce a single composite image made up of the in-focus parts of each photograph. I don’t pretend to understand how the soſtware achieves this result, but it works.
To produce a sharp image of a bee’s head, for example, might require 5–10 separate images to be stacked, depending on the magnification used. This is manageable using a camera mounted on the microscope, manually adjusting the focus between shots.
With the higher magnifications of extreme macro, the depth of field decreases, and the number of images required increases. An extreme-macro composite image may require many hundreds of images to be combined. To achieve this, some automation is required to take a series of photos, adjusting the microscope focus between each shot.
As an alternative to using a microscope, the camera and subject can be mounted on a rig which moves the camera closer to the
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