The first photographic strobes consisted of magnesium powder, ignited with much skill. Later, electrically fired flash bulbs with magnesium wire inside them, were used. These flash bulbs were designed to burn the magnesium wire completely and consistently and as fast as was feasible (about 1/250 second). It enabled photographers to bring light into dark places and to use it creatively. When the first images were produced with more than one source of light, they must have looked astounding, but nowadays we are so used to this. We expect television and theatrical shows to bathe in light from many directions, and that the light be used for creative effects. No doubt, one day such extravagance will enter the sea, but for now, the under water environment retains its innocence.
The flash bulbs were replaced with electronic strobes, producing light of daylight quality and of such intensity that they would discharge in 1/1000 to 1/10,000 second.

The reasons that strobe lights were used under water were firstly to capture its otherwise invisible colours. Armed with bags of flash bulbs, our early under water photographers were able to fascinate the public with pictures of an incredibly shaped and coloured world, never witnessed before. At that time, two types of flash bulb were available: the white bulb and the blue bulb. The blue bulb was corrected to produce light of daylight quality whereas the white bulb produced lamplight quality. Some under water photographers used both, preferring the white bulbs for subjects at distance. Unknowingly, they were experimenting with the colour corrections necessary for mixed light photography. They also discovered that flash light can destroy the under water atmosphere.

In this chapter we'll explore how to use ambient light to the full and how to introduce artificial light in such a way that it overcomes the disadvantages of ambient under water light while not being intrusive or introducing new problems.
 
 
 

Colour correction The problem constantly plaguing the under water photographer, is the quality of the light changing with distance travelled, as illustrated in this drawing. First the red colours disappear, then the oranges, yellows and finally the greens and purples. This colour distortion is very similar to that caused by clouds and can be corrected with warming filters and colour temperature correction filters. Note that these have an S-curve, unlike the bell-curve above, and do not correct the diminishing violet colours! Note also the difference between the notion of light path and subject distance. For most strobe-lit photography, the light path is about twice the subject distance.

Here are the most practical filters with their Cokin numbers and Kodak equivalents:

020: Full tungsten correction, blue (80)
021: Half tungsten correction, light blue
022: Cooling - very light blue (82B or 82C)

027: Slight warming (81B)
028: Warming (81C)
029: Half daylight correction, light orange
030: Full daylight correction, orange (85) as in all Super8 film cameras
047: Full daylight correction and warming; a bit brownish. Avoid this one.

Obviously, when correcting for the bluishness of the water, the warming filters 027 to 047 are used. 027 is too subtle to be of practical use but 028 is always necessary, even in close-up photography at 40-50cm distance. You will notice the difference! For macros (10-30cm) no correction is needed.

Use 028 for 0.7-1m light path
Use 029 for 1.5-3m light path
Use 030 for 3-5m light path and deeper still. Beyond 10m, these filters won't work anymore.
Use 047 with care since it makes the colours look rather brownish.
Note that full colour correction is not desired because for some reason the eye wants to see some of the underwater atmosphere.

Shallow seaweeds in a sheltered cove at Mayor Island, New Zealand. This photo, taken at about 2m depth was colour-corrected with a Cokin 030/ Kodak 85 full daylight correction filter. No flash light was used. The colours in the foreground appear normal, whereas those in the background progressively fade to blue due to their longer light paths. This filter can be used down to 2.5m depth for true colour correction but its effect remains useful down to 5m, requiring very little strobe fill light. Lens: 35mm effective (28mm  through a flat port)

Shallow seaweeds in Nursery Cove, Poor Knights Islands. Taken at about 1.5m depth with a Cokin 029 half daylight correction filter, the seaweeds show their true colours. No flashlight was used. Note that the light paths for the most important parts of this image are all about equally long, resulting in correct colours all the way to the surface. Lens: 15mm

A small school of Blue Maomao above Lessonia seaweeds in Nursery Cove, Poor Knights, New Zealand. Taken at about 3.5m depth with a Cokin 030 full daylight correction filter and no flash light. This is about the limit for full colour correction with filters alone. Schooling fish are usually very reflective, causing flash light to be mirrored back, invariably resulting in poor quality images. But in case the flashlight can becontrolled, a small amount of it would have made the fish stand out more. Lens: 15mm

Mixed fill with ambient correction filter Beyond 3m depth the daylight colour correction filters are not strong enough to fully correct all colours, but together with a small amount of flash light, they can. In fact, a half intensity neutral flash can almost always be applied between 8m depth and the surface while the (half) correction filter is in place over the lens. The fill light's most dramatic effect is that of softening harsh shadows while bringing colour to objects in the foreground. Because of its low intensity, there is little risk of scatter while the introduced shadows can hardly be seen. Hold the camera very still! Refer to the next section for more details. Note that the colour correction scheme with daylight correction filters applies particularly to waters that look blue. Those that look greenish due to light absorption by plant plankton, need correction filters that are purplish (magenta) in colour rather than orange. However, due to the fact that visibility also decreases dramatically in these waters, correcting the colours this way is of little practical value. The Cokin 036 magenta colour correction filter as is used to correct fluorescent light, is useful to some extent in green lakes.

A diver playing with a male demoiselle. While guarding their nests of eggs, these small fishes muster enormous courage to face up to much larger animals than themselves. But given time, the fish realises that no real threat is posed and is prepared to interact in a friendly way. This photo was taken at 6m depth with a Cokin 030 full daylight correction filter and a small amount of fill flash (about 1/3). In this manner full colour correction was achieved while retaining the underwater atmosphere and its transparency. Lens: 15mm

A snorkeldiver has descended to take a closer look at what occurs behind some rocks. This photo was taken at 4m depth with a full daylight correction filter before the lens, in order to correct the ambient light. A half intensity white strobe light was used to bring shape to the foreground and to light up the diver's face. All colours appear fully balanced. Lens: 15mm

Mixed fill light Although nearly every under water photographer uses some form of mixed lighting, the process as such is still poorly understood, resulting in disappointing images. The term mixed light implies that in some way the image is exposed by two sources of light, both adding to the film's exposure. One light source is usually ambient light, creating the underwater atmosphere and painting the background whereas the second light source is usually neutrally white strobe light. A mixed light image can thus be composed of 50% of one light source plus 50% of the other or any other combination adding up to 100%. For optimal colour rendition one wants more flash than ambient, which means that if the foreground is properly exposed, the background turns out too dark. It also leads to colours 'bleaching' towards blue due to insufficient colour correction. As you can see, this method can theoretically not produce optimal results, which is confirmed in practice. However, since the advent of super wide angle 15mm lenses that can be placed very close to the subject, it became possible to produce pleasing images. However, subjects that are entirely in the shade, while backlit by a blue sea, can give correct results.

The first drawing (above) illustrates a typical situation. Rather than showing the entire spectrum from violet to red, only two bars are shown for blue and red. Ambient light at a certain depth loses the reds and unbalances the colours (bars in bottom right corner). This is what the camera sees. By bringing in neutral flash light (equal bars), at even a small distance, the light becomes unbalanced resulting in more blue than red (bars above fish). What the film sees is an addition of both as shown in the bars behind the camera - clearly an unbalanced result, even if no appreciable loss occurred in the flashed light (use of super wide angle lens).
 
 

The drawing on the right shows the use of coloured light by placing a warming filter or daylight correction filter over the flash light. It introduces a reddish fill that combines with the ambient light to produce an almost perfectly exposed result (the bars behind the camera). This method gives satisfactory results, even with 100mm lenses for objects up to 1.5m away (a 3m light path). Note that the background will not be corrected since the filter is placed over the light rather than the lens, resulting in colourful objects projected against blue backgrounds. Note also that the background will always be exposed correctly. Another advantage is that scatter is reduced because the mainly reddish flash light scatters less and is less intense. Shadows become nearly invisible. One of the side effects of this method is that the colour of the fish fades from true to blue, which can be distracting when it happens to a model, but often the gradient from true colour to ambient colour is rather pleasing.

At some stage it is important to decide where to place the correction filter: before the flash or before the lens? Although this is also a matter of taste, I suggest: deeper than 10m it should be on the strobe (correcting for nearby objects) whereas shallower than 5m it should be on the lens (correcting for distant objects).

The main difficulty in doing mixed light photography is that of controlling the amount of strobe light, which is discussed later.

 

A male goatfish in spawning colours, resting on a yellow boring sponge. From this strategic location in the current, he masters his small but temporary territory. Near Leigh, New Zealand. This photo was taken with warm fill light using a full daylight Cokin 030 colour correction filter at a depth of 21m. Light source at half intensity and a tripod was used. Lens: approximately 100mm tele

The deep reef habitat starts where sea plants can no longer live through lack of light. It is inhabited by sessile animals like the orange finger sponge and yellow nipple sponges. This photo was taken at 25m depth in the Goat Island marine reserve, New Zealand. A full daylight correction filter was used before the light source which was set to a quarter intensity. A tripod was used. Lens: 50mm effective (standard Nikonos 35mm)

Through The Lens (TTL) light metering
Modern electronic cameras meter incoming light through the lens and control the shutter speed or aperture accordingly. These cameras have even become so smart as to be able to measure the intensity of the strobe light during its fraction of a millisecond duration and when sufficient, to turn the strobe off before that millisecond has passed. They are furthermore able to balance the accumulated strobe light to the ambient light. The balance can be set between 30% and 200%, giving an acceptable range of control. A disadvantage of such cameras is that the settings are rather awkward to change under water.

Modern cameras use the pre-flash method to assess the effect of the fill flash. Just before the actual exposure, the camera operates the flash several times with small pre-flashes, measuring their effect in the light metering quadrants (5 places in the image). Then it calculates the optimal light quantity and fires the flash accordingly while the shutter is fully opened. Note that remotely activated strobes may fire at the wrong time because of pre-flashes, and they too should be designed to follow the pre-flashing scheme. Please do not confuse exposure pre-flashing with that for red-eye removal. If you use a digital camera uner water, turn the red-eye pre-flash off! It just wastes precious time and upsets the fish.
 
 

Self-timing strobes
The first reliable way to control a strobe was by its own light metering circuit which measures the reflected light and stops the strobe when sufficient light has been emitted. In the earlier models the strobe's power was simply drained by another, invisible flash bulb inside the housing, thereby turning the outside one off. It resulted in a full power shot each time, draining batteries quickly while recycling slowly.

Later the 'thyristor' controlled units were able to turn the strobe off while retaining all remaining and unused power. These units used considerably less power and recharged quickly most of the time.

Controlling these strobe lights was simple by placing a neutral density filter before the optical sensor. Most units provided three to four settings. If these were not enough, a stepped neutral density filter could easily be made and placed before the optical sensor, even in the water!

Bringing such a strobe in balance with ambient light is done by choosing the 'aperture priority' mode of light exposure on the camera and setting the strobe accordingly. So for a given film speed, the four settings on the strobe could relate to f-stops: 5.6, 8, 11 and 16. Adding half flash light to an exposure using f11 on the camera, means choosing the f8 setting on the strobe.
This method works quite well and is easily adjusted under water, even when operating at 40m depth in a narked state. It is my preferred method, although modern cameras like the Nikonos RS do some clever thinking!
 
 

A young snapper (Pagrus auratus) has found a sea urchin and flees from the attention of other snappers. This photograph was taken at 5m depth with a full daylight correcting filter on the strobe which fired at 1/4 intensity, leading to a fully balanced subject while also showing the blue background. Notice the small amount of reflection and how the frozen red image gives sharpness to the whole. Lens: 35mm effective (28mm through a flat port)

The Nikonos5 under water camera
The Nikonos5 camera has through the lens light metering, including its strobe but has no settings to balance strobe with ambient light other than its factory settings. The problem is mainly that of reducing the strobe light in a reliable way so that colour correction can be applied. Placing a neutral density filter before such a TTL strobe won't work because the camera simply instructs it to produce more light. But there are subtle ways, once one understands how the camera's electronic logic works.

The Nikonos5 has a shutter that needs to expose for a minimum of 1/90 second or the shutter will be visible on the image. In that short period, all light integration takes place when the strobe is turned on. With the strobe turned off, light integration may take much longer, even for several seconds. So, by its design, all strobe-lit shots are destined to turn up with dark backgrounds - unless:

• A fast film is used, requiring an exposure of say 1/250 second before the strobe is turned on. The camera now forces 1/90s, thereby overexposing the background about 2 times. This works quite well and is relatively easy to control by means of its aperture but it requires sufficient amounts of ambient light and fast film.
• The shutter speed on the camera is set manually to 1/30s. This fools the logic which still integrates all light in 1/90s, but then keeps the shutter open for another 2/90s, exposing the background three times. At the 1/60s setting, the background is exposed 1.5 times. When using negative film, this variance in exposure falls within film tolerances and no further adjustments need to be made to the camera, but for slide film one may need to set the film speed somewhat higher (for less exposure). A difficulty of this method is that aperture settings have to be checked regularly and that the manual timing dial needs to be rotated from A to 30 and back many times.
• The strobe is exhausted before integration is reached. The camera then sees less strobe light and makes up the difference by leaving the shutter open until full integration is achieved. This is easy to do by turning the aperture setting to higher apertures and bracketing shots accordingly (first at f8, then f11, then f16). Some strobes show when they have exhausted their capacity. A disadvantage of this method is that the strobe recycles slowly while causing maximum battery drainage.

In manual mode, it cannot use the five segment light metering, and it resorts to wide spot metering. In the viewfinder, the amount of exposure is visible as a bar. Also the automatic shutter speed settings can be copied by manual adjustment. Adjust aperture and speed to expose the background correctly. The computer cannot change that. Now turn the over/under exposure dial -1 stop, to underexpose the strobe. This gives reliable and beautifully lit images. Use filters as required, and stop down to -2 where surreptitious lighting is needed. The disadvantage is always that dials need to be turned under water as soon as the light changes. fortunately for the RS, these are big and easy to operate.

Continuous movie light has its disadvantages too:

• A large battery needs to be carried. When compactly housed so it is heavier than water, while mounted on the dive tank, this saves some weight off your weight belt.
• Charging facilities need to be available. Design your system for 12 or 24 Volt standard, which is available in boats and cars.
• The light is weak, so it is most suitable for dark temperate waters. It requires fast film too.
• It is less suitable for fast moving subjects. Strobe light freezes their movements better, and gives more crispness, as also shorter shutter speeds are used.

At 25m depth in the currents running around Cape Rodney, beautiful gardens of sponges are found. In this picture at least four varieties can be seen. This photo was taken with two continuous movie lights without filters, balanced visually. The warm light completes the missing colours, giving a transparent look that retains the under water atmosphere. Only one shot was taken. No bracketing was necessary. Note how one branch was waving in the current. Lens: 35mm effective (28mm with flat port)
Despite their waters being turbid, many estuaries harbour delicate life forms which subsist in these conditions. A tritonia seaslug is seen feasting on its traditional food, a soft alcyonium coral. This macro photo was taken in extremely dirty water with large floating particles. By using tungsten light filtered with a full tungsten correction filter (020) while exposing for about half a second, all dust and scatter disappeared from the image while at the same time a view was opened to the deep background. On this photo the water looks much clearer than it actually was. Depth 10m. Lens: approximately 100mm
After having cannibalised another octopus which he is holding in his web, this male sand octopus has found refuge in the confines of a decaying crayfish pot. At a depth of 19m, tungsten light with a half tungsten correction filter (021) were used to highlight the subject of this situation. The vast amount of sand particles suspended in the water can hardly be noticed. Lens: 15mm