Strong lines, interesting shapes, recognisable items, colourful marine life, and a good story to go with the pictures - wrecks hold many attractions for underwater photographers.
     All the usual rules of underwater photography apply with wrecks: selection of lens, distance from subject, backscatter and flash positioning, shooting upwards to a light background, and balance of flash and natural light.
     We can take macro photographs of small marine life, portraits of the fish and other critters inhabiting the wreck, or shots of the wreck itself.
     Its this final possibility that we generally think of as wreck photography - the extreme wide-angle scene that says something about the wreck. Anything less is simply using the wreck as an artificial reef.

How big a scene should it be
Wrecks are big. Even major sections of a wreck on their own are big. So there is an understandable tendency to back off and try to get as much of a wreck as possible into the viewfinder.
     Backing off to the limit of visibility for this reason will normally achieve little more than a grey-blue smudge, perhaps with some of the foreground illuminated.
     Its a psychological problem that must be overcome. Try to resist the temptation to back off. As with any underwater photograph, you need to get in close. Pick a more constrained subject that dominates the foreground, leaving the big scene for the background.

Any wreck or this wreck
Sometimes all we are looking for is a nice photograph of a shipwreck - any generic wreck that fits the bill.
     This is fine for a while, but even really good images can begin to look somewhat monotonous unless they say something more about the wreck.
     To illustrate a particular wreck, look for subjects which others who have dived it will recognise, subjects that are unique to the wreck or that make a specific point about it (see panel).

Picture a diver, or picture the wreck
When I first started working on Divers Wreck Tour series, I dived a wreck that I had dived often in the past, so knew that I already had plenty of photographs in stock. I consequently left my camera at home and took only a sketch board.
     When the time came to write everything up and select the photos to go with the tour, I realised that I had a problem. I had lots of pictures of divers on the wreck, but none that really showed or identified the wreck in question.
     Divers can be used to good effect to add movement, scale and colour to a wreck photograph. But dont lose track of the fact that the wreck is the photographic model and the diver is the prop - not the other way round.

Picture a critter, or picture the wreck
To some extent the same applies to fish and other marine critters. Is it a picture of a fish where the wreck is a prop Or a picture of the wreck where the fish is a prop
     The distinction is not quite so obvious as with divers. There are many wrecks that are well-known for their inhabitants, so a picture of something swimming about in the context of the wreck is often a picture that says something about the wreck.

How wide a lens
I could say that the wider the lens the better, because wider lenses allow the biggest subject possible to be taken from as close as possible, and wrecks and their fittings are pretty big.
     But there are disadvantages. A very wide lens close to the subject will distort perspective. Closely related, it is difficult to illuminate such a wide field of view evenly, and also easier to end up with unwanted strays getting into the picture.
     My usual lens for wreck photography is a 14mm Sigma, a rectilinear lens (ie, not a fisheye lens) with a specified 114 coverage. Nevertheless, for those just getting into wreck photography a 20mm lens on a housed camera or 15mm lens on a Nikonos or Sea and Sea is much easier to use.

How powerful a flash
An average-sized underwater flash with guide number 20 to 25 is plenty for most wreck photographs.
     In typical UK conditions there is no desire to illuminate a more distant scene with the flash. All that would achieve would be more backscatter. Keep flash illumination to subjects no greater than 1.5m from the camera. Where natural light is available, use it to show background detail.
     Strangely enough, the best use of a really powerful flash is in clear and bright tropical conditions, where the extra power can be used to prevent excessive ambient light dominating a photograph.

How wide a flash
More important than flash power is flash coverage. Is the angle illuminated by the flash big enough to cover the angle seen through the lens
     One technique is to compose a photograph in such a way that fading flash illumination towards the edges will not matter. Flash coverage is needed only for the foreground subject, rather than the whole picture.
     Another technique is to use a diffuser to increase flash coverage, even though this comes at the expense of decreasing the effective flash power.
     This is not as big a disadvantage as it may seem. Any lens wide enough to need a diffuser on the flash will have a good depth of field, so widening the aperture to accommodate the reduction in effective flash power will rarely be a problem.
     The final technique is to use two flashes, not conventionally to eliminate shadows, but aimed slightly away from each other, so that one flash illuminates the left of the scene and the other the right.

How fast a film
Once the question of flash power and subject distance is settled, 100 ASA film is all that is needed for most wreck photographs. 400 ASA film is superfluous, giving a grainier picture, and unless the camera is set to a really small aperture using it carries the risk of flash light penetrating further and just illuminating more backscatter.
     If it is really good visibility and backscatter is not an issue, there will usually be plenty of ambient light. Using 400 ASA film will result in the scene being dominated by ambient rather than flash light, with the picture suffering from blue filtering.
     Having said that, there are two situations in which to consider using a faster film. When it is very good visibility, but relatively dark, the additional flash range can be used to illuminate more of the wreck.
     The second situation occurs when visibility is very poor but the water shallow, with strong ambient light. Blue filtering may be a preferable compromise to flash-light backscatter.

What fools automatic metering
All but the most recent top-of-the-range cameras meter flash exposure on the centre of the scene. Metering will be fooled into over-exposing the foreground in any situation in which it doesnt cross the centre of the scene.
     Typical situations are where the foreground is just a corner of the picture, with a bigger scene lit by ambient light in the background, or where there is a hole in the wreck at the centre of the scene, one example being a diver looking out through a window.
     The other thing that fools automatic metering is technical black.
     Its a sad aspect of UK wreck-diving that many of our dive buddies will be dressed in this horribly fashionable lack of colour.
     In both cases the answer is the same. Dont depend on TTL flash metering to get it right. By all means leave the flash set to TTL, but also use a lens aperture that is compatible with the distance between flash and subject.

Which way is up
Many wrecks are anything but upright, yet they contain many features that we visually associate with up and down. Even fish can get it wrong, some habitual wreck residents orientating themselves upside-down when swimming along a ceiling.
     A photograph can be much easier to understand if there is an unambiguous definition of which way is up.
     The easiest way to do this is with a diver, or more specifically with a diver and bubbles. Time the photograph so that bubbles do not obscure the divers face. Dont let bubbles dominate a scene - just a few trickling upwards are all that is necessary to provide that essential visual clue.

What can we do on a crowded wreck
Its not so much of a problem on UK wrecks, but in some tropical locations a wreck can easily have several boatloads of divers on it. Combined with good visibility, it can be quite difficult to keep them out of the background.
     Also, beware bubbles. A diver may be hidden from view, but it is surprising how easy it is to get a wash of bubbles across the corner of a picture, and how distracting it is in the final photograph.
     Patience when composing a picture is essential, but can also be futile. I lose count of the number of times I have a picture in my mind, but am just waiting for a shoal of divers to move out of the background. Then I am just about to be rewarded with a clear view when another group begins to cross.
     Most divers will be in or over the wreck, so the first technique is to take pictures looking outwards from on the wreck, rather than onto the wreck from outside it.
     The second technique is more to do with dive-planning. Dive either before or after everyone else!
     Diving before ensures minimal disturbance, but there can often be others who think of it as a race.
     On one overseas trip, no matter how early I started another diver in the group rushed to catch up and be ahead of me. In the end I signalled to my buddy and we made a dash for the other end of the wreck.
     Eric predictably rushed to overtake and get there first. Having dummied the opposition we doubled back and finally had the scene to ourselves.
     On a crowded site it is usually easiest to start last. Get into the water as other boatloads are ascending and be the last in from your boat. If you can cope with the current building up at the end of slack water, other divers will mostly be gone, the fish will be nicely lined up, and any silt stirred up will be carried clear of the wreck.

Going against all the guidelines, but it does capture the feel of the hangar deck of the Saratoga at Bikini Atoll.
Bales of tin plate identify the wreck as the Dakotian in Pembrokshire. The diver adds colour and scale
Furniture in the Prinz Eugen at Kwajalein Atoll. The wreck is upside-down, but who would know which way up the picture was taken Here, the picture has been turned into an upright and still looks right.
This photograph of the B17 Blackjack off Papua New Guinea goes to show that photographing the whole wreck does sometimes work. Only the upright propeller blade has caught any of the flash, the rest is natural light.
Big guns may be more impressive, but smaller guns are easier to fit into the picture. This is the machine gun on the destroyer Lampson at Bikini Atoll.
The mast of the trawler Three Brothers off Dingle shows lots of colour and strong lines and looks upward for a bright background.
There is not much wreck in the scene - nevertheless, the school of barracuda identifies the Duane off Key Largo.
Inside the Ikuta Maru at Kwajalein Atoll, where the wreck is on its side and the traces of blue through the holes misleading, but the diver makes the orientation obvious.
This huge cog identifies the dredger St Dunstan in Lyme Bay. The diver adds scale but the technical black kit is more like a black hole to light.
More a self-portrait than a wreck photograph, but the anemone-carpeted frame should be recognised by those who have dived the City of Westminster on the Runnel Stone.
The sewing machine is, as far as I know, unique to the Hirokawa Maru off Bonegi Beach in the Solomon Islands.
A formula propeller shot taken on the Bibb off Key Largo. It is shot close-up to capture the colourful marine-life growth.

THE WHOLE WRECK: Despite what I have said about getting close for a crisp and colourful image, if the light is good enough, the visibility clear enough, and the wreck small enough, it is always worth trying for a photograph of as much of the whole thing as possible. But dont waste your entire film on it.
THE SHIPS BELL: Bronze and shiny with the name engraved on it. I have yet to find one.
ARMAMENT: Anything from machine-guns to battleship guns, ammunition and torpedoes.
SPECIAL EQUIPMENT: Anything job-specific, like a dredging mechanism on a dredger or minesweeping equipment on a minesweeper.
WHEELHOUSE: The ships wheel, telegraph, intercom, compass binnacle.
ENGINE ROOM: Engine, ventilators, boilers, telegraph repeater, gauges.
ACCOMMODATION: Portholes, toilets, baths, furniture.
BOW: Anchors, anchor winch, chain, hawse pipes, bollards.
STERN: Propeller, rudder, steering quadrant, bollards.
DECK: Ladders, masts, cargo winches, pulley blocks, hatches, spare propeller.
HOLDS: Any recognisable cargo, from trains and trucks to perfume bottles. Propeller shaft and tunnel.