Strobe arms and their length is a very personal choice. Traditional logic aside, strobe arms should be a length that you are comfortable with and should not make your rig unmanageable either topside or underwater.
Of course, you could get by mounting the strobe directly to your housing or a handle, but we don't recommend that option. If you mount the strobe directly to the handle (one joint) you not only sacrifice flexibility and reach, but you force the strobe to fire along the same axis as the camera lens, which often results in backscatter and almost always produces unpleasant subject illumination.
A single-segment/two-clamp arm does not offer much flexibility in aiming the strobe 'outside the box.' Try this example: Rest your elbow in one spot on a table or desk. You can move your forearm and hand, but only in a fixed radius around your elbow. You cannot reach an object inside that radius. You cannot touch your elbow.
Our favorite setup is two arm segments and three clamps which not only gives you more extension, but lets you put the strobe exactly where you need it: up close for macro work or extended out for wide angle or creative lighting. Going back to our earlier example, now pick up your elbow from the desk. With the use of your whole arm again, you can reach almost any position in a hemisphere around your shoulder.
For new shooters or those with very small compact rigs, we suggest a 3" + 5" configuration. It is compact enough that it doesn't overwhelm a compact camera, and is easy to handle both in and out of the water.
A compact camera in a Nauticam housing and Sea & Sea YS-01 Strobe with Nauticam Flexitray, two Nauticam clamps, one 5 inch double ball arm, and one 5 inch single ball arm.
For this compact camera and two Inon S-2000 strobes, we have added a right handle to the Flexitray. On the top of each handle is a Nauticam 1 Inch Base Ball for Flexitray. Shown with the rig are two wet-mate lenses: an Inon UCL-165m67 Close-up Lens and a Fix UWL-28m52 Fisheye Lens. The double-ball arm on the right handle has an Inon Double M67 Lens Holder. When not in use, the wet-mate lenses can be stored in the lens holder.
A double-ball arm by Ultralight Control Systems
This set gives you plenty of reach to get the strobe well off camera to control backscatter and do creative things like side lighting macro subjects.
Remember, each clamp adds about an inch to the setup as does the strobe adapter, so the 3+5 arm set gives you a full 12" extension from the housing.
An XIT 404 Quad Ball Adapter attached to a T-Plate on the handle, provides a convenient mount for a video / focus light.
A closer view of the XIT 404 Quad Ball Adapter and Nauticam T-Plate
If you shoot a lot of wide angle work, you should consider longer arms for more reach in lighting large areas, but in most cases that involves more than one strobe. Also remember that the farther you put the strobe from the camera, the more drag it will create in the water.
So criteria boils down to personal preference, overall size of your rig and comfort level with the final rig as much as anything.
The nice thing about the double ball arm system is that it is completely modular, and we sell each piece individually so you can upgrade at any time without losing your investment in clamps, adapters, etc.
Two-strobe DSLR Rig
The photograph above illustrates a Canon 5D MK III in a Nauticam Housing with 45 degree viewfinder all set up for wide angle photography. This system is using electrical sync cables to the Inon strobes and four 8 inch strobe arms. The strobe arms on the left are mounted to a ball on the left handle and the strobe arms on the right are mounted to an M10 mounting ball directly to the housing. A lanyard with snap hooks is attached to one arm on each side; the lanyard provides a comfortable carrying handle for you as well as a "grab me here" point for when you hand your rig up to the boat crew.
Should you find that your system is a bit heavy underwater, buoyancy can be added by choosing buoyancy arms or by adding Stix Floats.
A Sea & Sea strobe mounted with one single-ball arm (strobe adapter), one double-ball arm, one Nauticam Carbon Fiber Float Arm and three Nauticam clamps.
Nauticam carbon fiber float arms are available in two diameters and in lengths from 6 inch to 12 inch.
This DSLR System With Standard Strobe Arms Weighs Approximately 3 Pounds In Fresh Water.
This DSLR System With Two Nauticam 8 Inch Carbon Fiber Float Arms Weighs Approximately 1+3/4 Pounds In Fresh Water
This DSLR System With Four Nauticam 8 inch Carbon Fiber Float Arms Weighs Less than 3/4 Pound In Fresh Water
An Aluminum Buoyancy Arm by Ultralight Control Systems Ultralight Control Systems manufactures buoyancy arms in many lengths and in two diameters.
This Fix Neo Video Light is held by a 1" clamp onto a ULCS 1/4 -20 adapter. The adapter is threaded on to an Ultralight Controls Tripod Clamp. Three 8 inch long double ball arms are inserted into the tripod clamp.
This configuration uses a Mounting Ball on the Nauticam Multi-Purpose Clamp to add a video light.
Ball adapters can be mounted directly to many housings in addition to those mounted on handles. You may wish to read this article with many photographs which illustrate mounting balls directly to the housing.
This configuration mounts the video light on a separate arm using two clamps and a Nauticam M10 Mounting Ball mounted directly to the housing.
Types of Arm Mounts for Housings
Mounting balls may be mounted on handles, on the 'cold shoe,' or directly to the housing. There are multiple choices for attaching mounting balls to housings, and multiple choices for attaching balls to handles as well.
Variations for attaching arms to housings include: T-Plate, Dovetail, M10, and 1/4-20.
A T-Plate type Flex Arm Base by Fix on a Subal Housing
Nauticam 1 Inch Ball Adapter for T-Plate on a Subal Housing
ULCS 1" Ball Adapter With 1/4-20 Stud for Ikelite Housings
XIT404 manufactures a Quad Ball Mount for T-Plates.
Cold shoe mounts are usually used with focus lights and can attach to ports or to housings.
Handle mounts also have the varieties of T-Plate, Dovetail, and 1" ball.
Nauticam 1 Inch Ball for Handles
Ultralight Control Systems 1 Inch Ball for Ikelite Quick-Disconnect Handles
T-Plate base for Nauticam Flexitray handles
Ultralight Control Systems T-Plate for Ikelite Quick-Disconnect Handles
When purchasing a strobe which uses AA batteries, don't forget a couple of sets of high quality NiMH rechargeable batteries and a world (multi-voltage) charger. If you travel to remote locations we always recommend a second charger for redundancy.