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PPDC Entomology lab


Dome lighting for insect imaging under a microscope

Common problems and their workarounds

Specimens with smooth, reflective surfaces may cast a mirrored image of the overhanging interior space of the dome. The reflection on the specimen will show the white interior dome walls and a noticeable black spot where light escapes through the dome's oculus (marked 'A'). This is the 'oculus reflection' effect. To the right shows an extreme example, Macraspis lucida, a highly reflective scarab.

You can see the oculus reflection effect in this sample, also.

Another problem with highly reflective specimens, is that the ring of LED bulbs at the base of the dome may be reflected along the margins of the specimen. This can be seen in the image to the right, marked 'A' (and above, along the margins of the scarab). This problem is created when the LEDs are angled inward enough to illuminate the specimen directly, from below.In some cases, the problem can be solved by simply moving the specimen down, closer to the stage.


The first step to reduce the oculus reflection problem is to be sure that the viewing hole is as small as possible, by stepping down the diameter using cover discs (shown to the right). This will reduce the size of the black spot while marginally increasing the amount of light in the chamber.

To eliminate specular effects that occur on the margins of the specimen (as in the wasp above), the LEDs may be repositioned to direct away from the specimen staging area and/or the specimen may be moved downward. If the problem persists, the LED bulbs may be shielded with a strip of plastic or Mylar so that the light is deflected upwards, along the sides of the dome, and does not reach the specimen directly.

The image to the right shows how an effective translucent shield may be designed and constructed. In this example, the shield was cut out from a bowl-shaped plastic container.

Although the dome creates a chamber with exceptionally diffuse lighting, specimens that have highly contrasted coloration may still present challenges for creating a balanced exposure where all elements of a specimen are properly illuminated (notice in this specimen the color difference between coxae and the base of the femora).

On the other hand, because of this exceptionally diffuse light, sculpturing details of a specimen may appear flattened due to the lack of directional light and appropriate shadowing.

Adding directional lighting may correct for these types of problems. Although some small overexposed areas remain, the image to the right was taken with a special dome (shown below) to address these problems and enhance light balance and sculpturing.

We have found that adding reflective surfaces, such as aluminum foil, to a section within the dome does not create an adequate directional lighting effect. However, the interior of the dome may be differentially painted so that light levels are unequal within the dome. For example, the interior half or quarter of the dome may be painted black, in contrast to the remaining white interior. The dome can then be rotated to reflect light accordingly and help ameliorate exposure or flattening effect problems. Domes like this may also help to mask the oculus reflection problem discussed above.

Domes that are translucent and allow supplemental flashes to penetrate the chamber walls may also be effective for creating directional lighting effects. A translucent dome setup invokes an additional set of technical hurdles, however, and we have yet to develop such a system that functions as desired.

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