Mini-test of INON D-200 strobes
Inon has released the D-200 as a successor for their D-2000 strobe, which is actually a simplified version of their Z-330 with a smaller guide number and without a separate electrical cable connection. The strobe's acrylic dome helps to spread the beam of light, which covers a full 110 degrees. The exposed dome of the strobe can be protected from bumps and scratches by keeping the diffuser on permanently.
Picture taken with Olympus M1 II in PT-EP14 housing without a port-dome. Olympus Zuiko 8mm fisheye, and internal flash trigger. ISO 200, F9, 1/50.
Compared with my former strobes, the Ikelites DS 161 (see my Blog of May 17), the major advantage of the D-200's are their smaller size and weight. The underwater weight of the D-200 is 4g/0.14oz negative including the Strobe Light Shade and 4 x AA Enelope batteries. The light output (guide number 20) was largely sufficient for some close-focus-wide-angle test shots that I tried on our window sill (see insert above). D-200 strobes with standard diffusers were set at a lower intensity (manual -4) setting, and placed close to the housing, pulled backward at the same level as the camera. I could not yet determine the merits of the rotatable shade caps of the strobes. I think they can be a handy device once you have worked out your specific lighting and flare problems underwater. The only problem is that you have to decide before the dive about taking of the caps, because it would be difficult to take them off during the dive. In the low -180 deg- position (used in the test picture), the cap can be useful to prevent reflections from a sandy bottom close to the camera. In the horizontal (90/270 deg) positions they may prevent backscatter, but also create a shadow in the center of the frame. The strobes can be triggered by using two optical cables, by either the camera internal flash or LEDS. One can also decide to use only one optical cable for the first strobe, and let the second strobe perform as a 'slave' to the first strobe with an adapter screwed on its sensor. The acceptable risk is that other photographers in your vicinity may also trigger your slave flash and an inconvenient time.
Selection of settings Settings on the rear panel to control the advanced circuitry of the strobe are pretty complex. The focusing light is controlled by a button at the lower left. The most simple flash setting described above is manual control with 13 steps of adjustment of the intensities of the flash (see the short article describing the Z330 which has the same control buttons on the rear panel as the D-200). The power selector has stops at both minimum (-0.5) and maximum (-6) power settings. Notice that variations in the intensity of the flash are achieved by very small changes in the duration of the flash signal on a msec scale. A second option is S-TTL, a technique that enables the strobe to perform in an optically slave-controlled TTL mode. In this case, you first need to release a button on the rear panel (lower right) to select pre-flash. Pressing the shutter-release button will then let the camera's built-in flashlight trigger the pre-flash signal via the control circuitry in the strobe, emitting a pre-flash to the UW object. The camera then 'sees' this pre-flash, judges the subject to be close to the camera, and decreases the power (duration) of the main flash by the camera, triggered by the built-in flash. According to the INON manual, the two requirements for using the fast S-TTL option of the D-200 strobe is a camera with a built-in pop-up or accessory flash to transmit light to an optical fiber, and the camera set to TTL or fill-in flash. Although I never use TTL, it remains interesting to follow the efforts designers of UW strobes and cameras make in further developing these techniques.