SEALUX CX910 systemflash housing

++ April 2014 ++ Review ++ by Werner Fiedler

SEALUX CX 910 The underwater housing for the system flash unit Nikon SB-910

Own brand system flash units communicate perfectly with their corresponding cameras. It would therefore seem obvious to use the artificial light source already purchased for conventional photography, under water, too. SEALUX can offer a suitable housing for the most sophisticated model right now, made by Nikon, the SB-910. Werner Fiedler put it to the test.

Basically, TTL flash exposure control has proven to be very reliable. However, this method of obtaining the correct exposure value of photos Through The Lens, was easier in the days of analogue photography. In those days the diffused light reflected off the film, directly proportionate to the right exposure value, was measured at the moment of taking the photo, and then the required amount of light was applied. This is no longer possible with a totally different reflection mode used in digital cameras. Therefore nowadays, before actually taking the photo, weak metering flashes are fired whose electronic analysis controls the main flash. It goes without saying that this process requires high-precision communication between the camera and the external flash unit. This communication happens according to a specific protocol determined by a processing unit which each manufacturer designs differently for almost every camera-flash combination, which he will keep secret in most cases. Manufactures of specialized underwater flash units and TTL flash converters quite often are confronted with insurmountable compatibility problems. This is why more and more of such units are equipped with optoelectronic solutions where the light pulse coming from the flash unit integrated in the camera synchronizes the external flash unit via a fibre-optic cable with the right amount of light. However, the complications set out can be circumvented using a system flash unit produced by the camera manufacturer which will always work with precision, even under water.

The housing

A system flash unit available in most cases anyway, its ingenious functionality and
high reliability are therefore sound arguments in favour of purchasing a suitable flash housing for your underwater camera. Now SEALUX can offer such a product for the latest and most sophisticated system flash unit made by Nikon. The housing was perfectly adapted to the SB-910, and the design also allows for sufficient space to fit an optional pilot light. Such a pilot light proved to be a very meaningful addition, even though the test housing available right now did not come equipped with it. A powerful but very low consumption (3 Watt) LED is installed conveniently close to the flash axis and runs on two fully-charged AA batteries for about three hours. It gives a bright light, equivalent to that of a 10 Watt halogen bulb. The pilot light cannot be dimmed.

The system flash unit housing is milled from a solid block and features a vertical partition. Both housing halves are held together by the same locking devices that have been tried and tested with all SEALUX products for many years. The front lens is a large-sized one because the LED pilot light might be installed underneath the flash reflector, if necessary. Another round window fitted at the front is meant for the sensor which is required for the automatic flash control without TTL, if the need arises. In the lid there is a flush-mounted control window for the display. Below, the controls are completely adapted so that all necessary flash functions can be used. The standard model features an N5 socket with fixed pins for the electrical connection with the camera. A rugged spherical joint head serves to fit the housing to the flash arm.

In action

Installing the flash unit inside the opened housing is easy, as it only needs to be pushed onto the shoe plate and locked to the same. It can remain mounted when replacing the battery. A continuous flange on the inside of the front part of the housing ensures the correct position of the lid when it is pushed into place. The two rapid-release locking devices which secure themselves automatically, finally push the lid onto the main seal (O-ring) which sits in a groove.

Although further above the advantages of the system flash unit were pointed out, a certain disadvantage needs to be mentioned, which is significant for underwater photography where, as is well-known, wide-angle lenses are popular. You can indeed expand the area covered by the flash unit by
placing the diffusing screen in front, but thereby the maximum light output is reduced without even attaining the illumination angle achieved by specialized underwater flash units. This is relevant all the more as the flat housing front lens has the effect of significantly reducing the angular field of the flash light cone as it enters the water. To get the best illumination for wide-angle shots it is indispensable to flip the diffusing screen in front of the system flash unit. By contrast, for macro photography the normal flash beam width is always sufficient. For close-up shots the TTL flash control always provides precise exposure results. For all other applications the unit can obviously be operated manually with the greatest of ease.

The housing with the system flash unit inside has neutral buoyancy so that the diver’s camera work is not impaired. Moreover, the ball joint swivel arm available from SEALUX as accessory allows a very variable illumination of the subject or scene. Those who can do without the extremely large angle of illumination of a specialized underwater flash unit will obtain very good results with a system flash unit inside the housing.

SEALUX CD7100 Review Technical Data

Material seawater resistant aluminium alloy
Surface hard anodized + titanium grey special coating
Front lens flat lens made of organic glass
Housing locking devices 2 spring-loaded quick-release locks with safety catch
Control/function windows 3
Function transmission devices 8 (9 with pilot light)
Accessory attachments 1 ball joint end piece, 1 M6 thread
Sync cord socket 1 N5 flash socket (as standard) (optionally with spring-loaded N5 socket or S6 socket)
Dimensions W x H x L 124 x 229 x 165 mm (including ball joint end piece, locks and caps)
Weight (without flash unit) 1.35 kg (version without pilot light)
Buoyancy (with flash unit) virtually neutral
Maximum tested depth 90 m