Nuts & Volts - January 2007

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I initially became involved in macro — or close-up photography — as part of my job, which involves failure mode analysis of electronic circuitry. Be sure and read the sidebar for a discussion of why photographs of small objects are called macro photography.

BUILD A RING FLASH FOR

MACRO

PHOTOGRAPHY

With components

becoming smaller

and smaller, taking a

decent photograph

has proven to be

increasingly difficult.

but these can be expensive.

Fortunately, with component miniaturization and with the newer, high brightness white LEDs, it is possible for the hobbyist to build one. Figure 2 shows the assembled project on my old trusty Sony CyberShot. If your camera has a threaded front lens and a non-dedicated flash hot shoe, you may benefit from this project.

■ FIGURE 1. A fine application for macro photography — documenting your coin collection.

Ireally became interested in macro photography after realizing how extensive my son’s coin collection had grown. Loving photography, I immediately though about documenting his collection. I had faced challenges at work, but capturing the exquisite detail found in many coins, such as the example shown in Figure 1 — a post-World War 2 British penny — was a bit trickier.

The main problem stems in that for macro photography, one has to come very close to the object being photographed, usually no more than a couple of inches from the lens. Although newer cameras and lenses can handle this extremely short focusing distance, the challenge lies in how to illuminate the object, as the camera and photographer project shadows into the object. Low light conditions lead to uneven contrast and require both slow shutter and wide apertures, which result in blurry images and a shallow depth-of-field. The solution to this issue has been to employ lens-mounted ring flashes and illuminators,

Circuit Description

■ FIGURE 2. The completed project mounted in a camera. On the camera’s top is the power pack; on its lens, the LED ring.

White LEDs are a major improvement over incandescent lamps for portable illumination, and in particular for photographic use. They are rugged, their color temperature does not change dramatically with weakening batteries, and they are far more efficient in the electrons to photons conversion. Unfortunately, they cannot be connected directly to a voltage source; its current must be regulated. This is traditionally accomplished with a ballasting resistor, which is very wasteful.

For the large number of LEDs — 15 in total — required for this project, a switchmode power supply is required. Since white LEDs each have about 3. 5 volts forward drop, and there are five of each in the three series, a boost topology is mandatory.