Lepidoptera
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Hands-On Experience: Sigma EM-140DG External Ring Flash
With our Olympus D620L and E-20 cameras, the built-in flash was effective for lighting the subject in just about any situation. Even with close-up photography, including the use of the Olympus MCON-35 macro extension lens with the E-20, the built-in flash was high enough above the camera body to prevent the shading of the subject by the camera lens. This is not, however, the case with the built-in flash on the Nikon D80 which, together with our chosen Nikkor lens, casts a heavy shadow across the middle of the field of view when used for close-up shots. A small moth in the center of the frame, at maximum magnification, is typically 50% to 100% within that shadow, a less than satisfactory result for our main application.
Normally I center the subject, in this case the pretty pyralid moth Eurrhypara hortulata, to take best advantage of the auto-focus. Unfortunately, getting a good close-up at night with flash also means that the subject is mostly hidden in the shadow of the lens because the built-in flash isn't physically high enough to light the center of the frame.
A number of electronic flash solutions were therefore evaluated. Because of the close working distance between the lens and the subject, a lens-mounted flash was the preferred solution.
Nikon does not have a true ring flash unit, and the Nikon Closeup Speedlight Commander Kit R1C1, with its flash units mounted on arms attached to the sides of the lens, seemed likely to invite accidental damage in the lively chases of flying moths that are common to our application. The projections to the sides also had the potential to interfere with getting a straight shot along the surface of a wall for side views of moths that don't sit flat. As well, we came across comments about the weight of the lens-mounted dual flash units causing excessive wear to the focus mechanism on some lenses.
The Sigma EM-140DG, however, is a highly rated flash, similar in form-factor to a ring flash, and specifically designed for macro or close-up photography. It is available in versions compatible with a number of camera manufacturers (and in a fit of inscrutability, models for different camera makes all carry the same part number — differentiation is in the word Nikon, Canon, Olympus, Sigma, etc. printed on the box).
The Sigma EM-140DG ring flash mounted on our Nikon D80's
Nikkor AF28-105mm f/3.5-4.5D IF normal/macro lens, plus
the Olympus MCON-35 macro lens and Sigma adapter ring.
The battery pack and control unit mounts on the camera
hot shoe like a normal flash. It is fully compatible with all
camera automation and control.
The Sigma EM-140DG has a guide number of 14/M ISO 100, and includes two independently adjustable flash modules, fixed 180 degrees apart. It is made up of two parts. The battery pack with electronics is attached to the D80's hot shoe on the top of the camera's viewfinder, just like a regular flash. A short coil cord runs from the power module to the flash module, which is attached to the front of the lens by means of a screw-on adapter ring.
The adapter rings are available in variety of standard diameters up to 75-mm to accommodate different lens diameters. Attaching or removing the flash head is easy, as one just has to squeeze two buttons to release the unit from the lens' adapter ring. This is a great convenience, because we continue to use the Olympus MCON-35 macro extension lens for next-day retakes of any moths that have been collected for further study, typically including some of the smallest species. Our regular Nikkor macro zoom lens takes a 62-mm adapter ring, while the MCON-35 takes a 72-mm adapter ring.
This picture shows the Sigma ring flash's control panel on the
rear of the power unit. Each of the two flash tubes may be
individually adjusted for artistic lighting effects.
The Sigma flash is fully compatible with the latest Nikon digital cameras, supporting all the operational modes and automatic functions included with the camera.
The flash is powered by four AA batteries; rechargeable NiMH or NiCd batteries are recommended. The flash unit battery life seems to be similar to the D80 camera's battery life, probably averaging in the order of 500-600 pictures before need to recharge, using 2000 mA-hour NiMH cells and perhaps an average flash-to-subject distance of 2 cm. This Sigma flash would be perfect if it included a battery charge level indicator like the D80 camera does. Instead, it's prudent to carry a spare set of batteries in case of need.
As a bonus, the manual for the Sigma EM-140DG is well written and nicely printed. In addition, the flash comes in a handy, well-padded carrying case with lots of pockets for the various small bits, spare batteries, adapter rings, etc.
