Divernet


HOUSINGS FOR COMPACT DIGITAL CAMERAS provide a great entry into underwater photography. Once familiar with the basics, the obvious question for those looking to develop their photographic skills is: What bit of camera kit should I buy next
Should it be a supplementary wide-angle lens Not yet. To get worthwhile results from such a lens needs better lighting than the built-in flash can provide.
Should it be a red or orange filter to improve colour balance Filters definitely have their uses, but a filter can do nothing to illuminate shadows - and can do nothing if there is too little light in the first place.
The one bit of kit that enables compact digital camera users to make big advances is an external flashgun. Its light can bring out the colours in most subjects. At the end of a long arm, or held by hand clear of the camera, it will also greatly reduce backscatter.
Lack of colour and excessive backscatter are the most common technical problems with underwater photography. Solve these problems and all thats left is to find the right subject and compose a nice picture. If only it were that easy!

How far away can the subject be
hspace=5 THE RANGE OF FLASHGUN LIGHTING depends on four factors: the power of the unit, the sensitivity (ISO setting) of the camera, the lens aperture and the clarity of the water.
In the camera electronics, higher ISO sensitivity incurs more electrical noise from the sensor chip. Compact digital cameras have physically smaller sensors than SLR cameras, so they are inherently noisier, even if they have the same number of megapixels.
A low ISO sensitivity setting means that the sensor is less sensitive to light, so reducing the effective range of the flashgun. A high ISO setting increases the effective range of the flashgun, but at the expense of more digital noise in the picture.
As a further handicap, noise will be greater in darker parts of a picture, and underwater scenes tend to have heavy shadows.

Tip: Use the lowest practical setting, ISO 50 or ISO 100

A wider lens aperture allows more light through, and so increases flashgun range and the effect of ambient light. Working against this, aperture also influences the depth of field, or how much is in focus. A smaller aperture gives more depth of field.
Table 1: Max range for ISO sensitivity and aperture
ApertureFlashgun range
 ISO 50ISO 100ISO 400
f2.82.5m3.5m 
f5.61.2m1.8m3.5m
f80.9m1.2m2.5m
This is where a pocket digital has quite an advantage over bigger SLR cameras. The lens and sensor are so small that even wider apertures still give reasonable depth of field.
So while a pocket digital needs to use a lower ISO sensitivity to reduce noise, this can by compensated for to some extent by using a wider aperture.
When it comes to power output, a typical underwater flashgun will have a guide number of about 20 (a measure of power).
Table 1 shows the theoretical range at which such a flashgun is effective.
A range of 3.5m at ISO 100 and f2.8 may seem quite good, but the corners of a picture are further away, and we also need to take account of water clarity and blue filtering.
Just as ambient light is blue-filtered with depth, so is flashgun light with distance from a subject.

Tip: Flashgun light is ineffective for subjects further than 2m away

Even with a flashgun, natural light filtering from above can have a significant impact on both exposure and white balance.
For nice bright photos with plenty of colour, we need the flashgun light to dominate. At the same time, if we want to see the background of a scene, we need to keep some natural light.
The effect of flashgun light is controlled by ISO sensitivity, aperture, flashgun power and subject distance.
The effect of natural light is controlled by ISO sensitivity, aperture and shutter speed.
If the camera does not have a manual setting and the flashgun is set to automatic exposure, the only remaining factor that we can use to make flashgun light dominate is subject distance. We need to be very close.

Tip: You need to be able almost to reach out and touch the subject (0.9m)

When a camera has a manual setting, we can control shutter speed independently of the aperture. If the internal flash can be set to manual we can use power settings on the external flashgun for full, 1/2, 1/4 power etc.
Now we can use any or all of subject distance, flashgun power and shutter speed to have much more control of the balance between flashgun and natural light.
We can also use aperture and ISO sensitivity to control the overall brightness of the picture.
Back in the days of film, getting this lot right was part of the black art of underwater photography. With digital, we can simply review the results and correct the settings as we go.

Which white-balance setting
hspace=5 DIGITAL SENSOR CHIPS separately detect the red, green and blue in a scene and mix them to give the final colour. The white-balance settings of the camera decide the proportions in which red, green and blue are mixed, and so control the colour of the final picture.
Without a flash, the only source of light would be blue filtered natural light. With a flashgun, we add white light to the foreground.
For close subjects, the flash light will dominate and blue filtering of the flash is insignificant. For distant subjects, there is a finer balance of flash and natural light, and the flash will be slightly blue-filtered.

Tip: For close ups, set the white balance to flash. For scenes, set the white balance to cloudy

Some cameras have an underwater setting for white balance. Dont use it. It isnt designed to take account of light from the flashgun.

FLASHGUN POSITIONING
hspace=5 AN EXTERNAL FLASHGUN doesnt need to be beside the lens, and thats a big plus. By moving away and angling it inwards, we can still illuminate our subject while reducing backscatter from any bits in the water.
Think of the camera, flash and subject being on the corners of a triangle. When the camera-to-subject distance changes, that breaks the triangle unless we reposition the flashgun. But dont leave this to last, as it could scare our fish.

Tip: Set the flashgun position before approaching a fish

The flashgun will throw a shadow on the opposite side of our subject, so we need to think about how this will affect the photograph. Shadows are part of the way in which we see the world, so are not necessarily a bad thing. The trick is to make it look natural.

Tip: Begin with the flashgun above and slightly to the left

hspace=5 Lighting from over the viewers left shoulder is a trick from classical art that usually works for the human eye, so its always a good starting point. If the shadow looks awkward we can try variations, moving the flashgun from left to right. Perhaps we can get the shadow to fall into open water, where it wont be noticeable.
We can also try moving the flashgun closer to the camera, trading off the risk of backscatter for shadow position.
You may be tempted to add a second flashgun, but dont spend your money yet. Master one before complicating things.

External Flashgun
hspace=5 Pocket digital cameras and the housings for them do not have connectors for a flashgun cable as SLR cameras do. The only way to trigger an external flashgun is as a slave from the cameras internal flash.
But in doing so, we dont want any light from the internal flash to get in front of the lens and cause backscatter, so it has to be shaded from throwing any light forwards.
Some flashgun kits for digital cameras come with a clip-on shade.
hspace=5 In the case of my camera, I just put a few strips of black tape on the slot-in diffuser.
The simplest and most reliable way to connect a flashgun, also the cheapest for anyone starting from scratch, is with an optical fibre.
This catches the light from the internal flash and relays it to a sensor on the external flashgun. When the internal flash fires, so does the external flashgun.

How big a subject can fit into the picture
Given the maximum range at which we can use a flashgun, what can we fit into a picture Most compact digital cameras have a zoom lens with a wide-angle equivalent focal length of 35mm (equivalent to a conventional 35mm film camera) and some start as wide as 28mm equivalent.
Under water, the flat glass of a housing has the same effect as looking through a divers mask. The angle of view is reduced, and everything appears closer (see Table 2).
Table 2: Lens diagonal coverage in air and water
35mm film
equivalent lens
Lens diagonal coverageDiagonal size at range
AirUnderwaterrange 0.9mrange 2m
28mm75°54°0.9m2.0m
35mm63°46°0.7m1.6m
Underwater users of SLR cameras consider wide-angle to mean 90 or more, but a compact digital achieves just over half that at its widest setting. Even a wide-angle lens is not really wide-angle when used under water.
By the time we have allowed for a bit of space, and that we rarely fit a subject all the way across a diagonal, we should be thinking of composing pictures half that size, about 35cm at 0.9m away.

hspace=5 Tip: Get close and a digital compact is ideal for shooting fish

All we need do is find a fish that wont swim away while we poke a camera at it. Ever wondered why so many photos are taken of scorpionfish, lionfish, crabs, lobsters and so on Theyre easy targets!

Tip: Look for subjects that dont swim away

What if its bigger
hspace=5 IF A SUBJECT IS TOO BIG to fit in the viewfinder, try to avoid moving back. Staying close usually results in a better photograph.
If a fish is too big to fit sideways-on, how about taking a portrait from directly in front, or across a diagonal We can also look for a composition using only part of the subject, perhaps just a face or head and shoulders rather than the entire critter.
Such intimate compositions can make a striking picture, and its worth looking for opportunities to get close, even zooming into the face or head and shoulders of smaller critters.

Tip: Get intimate with a critter - photograph its face

What if its smaller
IF A SUBJECT IS SMALLER, the first option is to get closer, reducing the amount of water in the way and also backscatter. It will also increase the lighting from the flash, so we can lower the ISO sensitivity and reduce noise.
The next step is to use the optical zoom (but leave any digital zoom disabled). When we get really close, with many compact cameras the aperture does not go small enough to limit the flash light, so the photo could end up over-exposed.
Our options are to reduce the flashgun power, put a diffuser over it or move it back. There is no reason to keep the flashgun alongside the camera.

Tip: Altering flashgun distance has greatest effect when we are close to our subject

My fish moved!
hspace=5 DESPITE THE CONVENIENCE of subjects that sit still, there comes a point when we want to photograph a moving fish. This is a difficult prospect even with the instant response of an SLR camera, and probably the most difficult subject for a compact camera that suffers from shutter delay.
Thats a shame, considering that the lens is quite well suited to fish photography.
We need to predict the movement of the fish, then be in position to take the photograph with
the camera and flash already set, the camera pointing in the right direction and the shutter triggered at the right time.
Predicting and controlling your own position is down to good diving skills. Predicting the shutter delay is something that can be learned by getting a feel for the camera. Predicting the behaviour of a fish comes from studying fish generally and your subject in particular. It also helps to let a fish settle down and become more accustomed to the diver.

Tip: If a fish is circling or following a repetitive pattern, start counting and do it by numbers

hspace=5 One, two, three (move in), four (start panning camera), five, six, six and a bit (trigger shutter), seven and flash fires, eight (keep panning for natural light). Give it a few repetitions before clicking the shutter. It may take several more repetitions to get it right, but thats the beauty of digital; were not wasting film.
Use a similar technique to catch the interesting parts of anything repetitive - kelp moving with the waves, a moray eel opening and closing its mouth or a cleaner wrasse moving about the face of the fish being cleaned.
Even if the behaviour of a fish is not completely repetitive, parts of its behaviour may follow a set pattern.
Take trevally or barracuda swooping through a cloud of juveniles. We cant predict when the action will happen, but once it starts, we can predict its course.

Catching the one-off shot
hspace=5 WITH ALL THIS PREDICTION, there remains the one-off shot where something comes out of the blue and is gone before we have time to do anything other than hurriedly point a camera in the right direction and press the button.
The answer is to be prepared. Whenever were not working on a particular subject and just swimming along, set the camera and flashgun for the most likely or wanted encounter.
That way, when it happens, we dont waste any time.

Tip: Keep the camera pre-set and ready for a lucky encounter

The equipment John used
hspace=5 All underwater photographs shown with this article were taken on a Canon S70 compact digital camera in a Canon WP-DC40 housing (neither available today but they cost 420 three years ago). A single Sea & Sea YS90 flashgun (also obsolete, 160) was triggered via a Heinrichs-Weikamp digital adapter (100 euros, heinrichsweikamp.net) and cable (100).
This enables John to use flashguns from his SLR system, but if starting from scratch an optical fibre is a better solution. Current flashgun options include the Sea & Sea YS110 (399) and Inon Z240 (490).
hspace=5 The flashgun arm and tray were home-made for about 25, but many commercial equivalent products are available at around 200.
Photographs were taken in RAW format at the cameras maximum 7-Megapixel resolution. ISO settings ranged from ISO50 to ISO 400. Adobe PhotoShop was used to adjust colour, retouch backscatter and provide further noise filtering.

  • Further information: marine-cameras.com; camerasunderwater.co.uk; oceanoptics.co.uk