Ocean Leisure Diving and Photography Blog

  • It Used To Be Not If, But When!

    Anything taken underwater that has an air-space within it will have a tendency to leak. This sad fact of life used to be never more true than with cameras. There was even the once ironically named Society of Nikonos Flooders! So the philosophy of underwater photography combined with the realism of the likelihood of a flood coined the advice, “It’s not if, it’s when.”

    So why does something that is designed to keep the water out, let the water in? Well, it’s all down to the fact that you need to access a submarine housing from time to time, whether it is to renew a battery or replace a memory card. The seal at the point of entry is usually effected by an O-ring that sits it a groove and abuts another surface when the unit is closed up. If the point of contact between the O-ring and these surfaces is not scrupulously clean and smooth, free of any foreign bodies like hair or grit, the seal will be broken and water at the pressure of depth will hose through the so-caused gap.

    The O-ring must be lightly greased. This does not help it seal but simply allows the O-ring to flex and move as the two surfaces are offered up to each other. Too much grease can in itself cause a leak. You should just put on enough to make it glisten.

    Passing a clean O-ring between your lips can help you detect if it has any grit or hair clinging to it and you might do this before you re-grease it. O-rings are often supplied with camera housings as spares but the original will never wear out. You would need to damage it with a sharp object for it to need replacing.

    So keeping the opposing surfaces smooth and clean and placing a clean lubricated O-ring between them should maintain a perfect seal – but bad things can still happen. Using the wrong type of grease can cause a leak. If you use silicone grease on a silicone O-ring, it can cause it to swell or start to dissolve. Use the right grease - an environmental silicone - even on neoprene O-rings.

    Don’t leave your rig in a fresh water rinse tank. Other divers may not be so careful about your precious kit and a careless collision with another object being rinsed could cause some catches to come undone.olympus_tg4_package_1

    Isn’t there a better way? Well, yes there is. If you want a compact camera, what about the Olympus TG4 in an Olympus housing? You will need to maintain the main O-ring of the housing in much of the same way as you would any other make of housing but the TG4 has a second line of defence in the event of an ingress of water into it. The Olympus TG4 is itself an amphibious camera and can be used down to 15 metres deep just as it is. Put it inside it’s housing and, should the housing be found to leak, you will only need to ascend to 15 metres deep and later, open the housing and rinse it in some fresh water and dry it, before you are ready to reinstall it in its housing, first having discerned what caused the leak in the first place.

     

    nauticam_na_g7xIf you go for a compact in a more elaborate housing, buy a Nauticam and spend the additional £191 on a vacuum leak-test kit. These vacuum leak test are available on bigger more expensive Nauticam housings for bigger and more expensive cameras and nobody in their right mind would eschew the chance to never suffer another leak again.

    The vacuum leak test as an integral part of a housing was first introduced by Hugyfot. These housings are available only for more expensive cameras but when they were first introduced many years ago, several owners suffered flooded cameras. The problem was that these housings are securely sealed and locked using bolts. These bolts were sometimes not fastened tightly enough and when the clamshell housing was pushed together by the intense pressure found at depth, the bolts could work loose. When the diver ascended to a lesser pressure, the two halves of the clamshell housing could become loose and a flood was the result. The Hugyfot vacuum leak-test was the answer to this problem (now included as standard equipment on all Hugyfot housings) and Nauticam has more-or-less adopted a similar system.hugyfot_canonmk3_front

    This is how it works: The camera is sealed inside the housing with a lightly lubricated O-ring to seal out water, as usual. A pressure sensor within the housing confirms it is working and a (red) LED signals that the air inside the housing is at the same pressure as outside.

    The air is then vacuumed out of the housing via a special one-way valve using the pump provided. The pressure sensor inside detects that the air pressure is suitably reduced and a green LED shows. Green is good.

    The user then waits to see if the green light remains or whether a red light will show instead. It is recommended to wait around 20 minutes. If no air has leaked in, no water will leak in. Depressurizing the interior of the housing has a secondary benefit. Outside air pressure pushes the two parts of a clamshell housing together so firmly that you need not do up any bolts or close catches (should you forget) and you literally cannot prize the two parts apart without letting air back into the housing via the valve provided.

    nauticam_5dsrSo this cured at one stroke, the problem of Hugyfot users not fastening the housing bolts sufficiently, as well as ensuring there was going to be no leak. Hugyfot cured this design/user defect at one stroke.

    Underwater photographers find that winking green light to be very comforting on a dive and never open the valve to let air into the housing until they are out of the water and done using the housing. Now it’s not not-if-but-when, it’s green ensures your costly camera will survive!

     

     

     

  • Truk Lagoon - a Trip of a Lifetime

    During World War II, Truk Lagoon became the forward operating base for the Imperial Japanese Navy in the South Pacific and as such it was thought to be an impregnable fortress. More than 27,000 men were stationed there and the islands surrounding the lagoon were equipped with roads, bunkers trenches and artificial caves. There were five airstrips, a seaplane base, submarine repair workshops, a torpedo boat station and all defended with heavy guns, anti-aircraft guns and mortar emplacements. Some have described it as Japan’s equivalent of America’s Pearl Harbour in Hawaii. They even had time to remodel an island so that it looked like an aircraft carrier from the air!

    Battle tank on the deck of the San Francisco Maru Battle tank on the deck of the San Francisco Maru

    It was feared by the American Command because they considered that to take it would cost a lot in American lives

    In February 1944, despite the main body of warships escaping to Palau after an American reconnaissance plane was spotted, a massive attack by American bombers flying from a task force of aircraft carriers destroyed the military effectiveness of the Japanese base in Truk (Chuuk)  with 32 Japanese merchant ships (operating as fleet auxiliaries) sunk. Operation Hailstone as it was known resulted in Truk becoming the biggest graveyard of shipping in the world.

    One of the many telegraphs on the Shinkoko Maru One of the many telegraphs on the Shinkoko Maru

    Given the poor state of the Japanese war effort in 1944, few of these vessels had much fuel in them and the amount of pollution was minimal. Though today, most of them are in a poor state, these wrecks make exciting dives and give an insight into life at sea during that period. Most of them are in water shallow enough to be accessible by any open water diver and some of them are metamorphosing into colourful reefs.

    Sight glasses on the engine of the Kansho Maru Sight glasses on the engine of the Kansho Maru

    It’s a long way to travel from the UK, via Singapore, Manila, Guam to Chuuk, but it’s a scuba diver’s trip of a lifetime and should not be missed. If you go, remember to go equipped with some sort of camera so that you can bring back memories of your experience. The most interesting parts of the wrecks are their engine rooms and cargo holds so you will need some effective lighting in order to capture rewarding images. You’ll need an underwater strobe together with an aiming light that automatically extinguishes when you take a still picture. For video, you’ll need powerful video lights that give even illumination across the field of view. A wide-angle or fish-eye lens is essential if you want to capture more than details, so don’t go without one.

    Submarine periscopes in a companionway of the Heian Maru. Submarine periscopes in a companionway of the Heian Maru.

    It’s a pity to go all that way and find that you regret saving the cost of the right equipment to take with you!

    Come into Ocean Leisure Cameras and discuss what equipment you need to come back with meaningful images of your trip of a lifetime.

  • Underwater Photography - A Masterclass

    There was a time when great underwater photographers, the likes of Chris Newbert, David Doubilet, Jeffrey Rotmann, Roger Steene and Norbert Wu, published coffee table tomes of their wonderful photographs, but nowadays, few people buy this type of book. When National Geographic sheds its full-time photographic staff, it indicates what dire straits the publishing business might be in.

    The digital revolution has changed underwater photography, and now everyone wants to take their own pictures and share them on-line. It has become remarkably easy. Ocean Leisure Cameras can supply the hardware for you to do this, from a housing to accommodate your iPhone, the remarkable yet tiny GoPro POV cameras, easy-to-use compacts like the Olympus TG4, the Olympus E PL7 or even a submarine housing for highly sophisticated DSLR.

    In the wake of this digital revolution, a plethora of underwater photography gurus has sprung up promising to reveal the differences between photographing through water rather than air, and the solutions to that, whether it be wide-angle or fish-eye lenses, light balancing filters or underwater lighting.

    Some of these gurus are self-styled and not necessarily very good, but marine biologist and underwater photographer Alex Mustard is the modern master of what he does, and willingly reveals to others, by way of escorted photo-safaris, how he does it. Instead of producing just a coffee table book of pictures, he is more didactic in his approach, disguising his superb photos in this book as demonstrations of how to do it, or rather as an inspiration to others to have a go themselves. It’s a master class and it’s stuffed with information.Underwater Masterclass cover

    The text is written in an informal and chatty style. Unlike many how-to-do-it books, it’s not full of pretentious twaddle and demonstration pictures covered in arrows. Nevertheless, he’s covered every aspect of the subject and filled its 190 well-designed pages with examples of exceptional underwater photography that any diver with a camera would wish to emulate. In fact, they could represent the modern day acme of any underwater photographer’s achievements.

    That said, it makes a good stand-alone read. For example, the chapter on Close-focus wide-angle starts, “A mantra for successful underwater photography is “Get close. Get CLOSER!” This is such essential advice that some photographers even have it written on the backs of their housings.”

    Underwater, wide-angle lenses are not used for getting more in. They are used for getting closer without cropping anything out.

    At the start of a chapter entitled ‘Big ideas for small subjects,’ he writes, “Some photographers look down their noses at macro photography, mistakenly believing it lacks the creative art of wide-angle.” Again, Ocean Leisure has a range of macro (close-up) and super-macro lenses.

    If you are already satisfied with the pictures you are producing underwater, buy this book and let your envy work wonders for you. If you have never taken a picture underwater, buy this book and get persuaded you can do it, too. In the age of digital photography, it’s easy. With the Underwater Photography Master Class, the secrets are out and you can buy a copy from Ocean Leisure Cameras!

  • Know What Your Computer Tells You!

    Depth and Ignorance Can Kill. Was it the lure of depth, his lack of awareness of how deep he was, or the inability to understand his computer? According to witnesses at a Cayman Coroner’s Court, Victor Crawford, a 62-year-old diver from Alabama and passenger aboard the Cayman Aggressor, had dived to a depth of 95 metres whilst using nitrox with a maximum operating depth of 33 metres. Health Services Authority pathologist Dr Shravan Jyoti said the cause of death was seawater drowning as a result of ‘nitrogen toxicity’.

    Mr Crawford went missing in March last year during a group dive before divers from Ocean Frontiers, a well-known Cayman technical diving operation, discovered his body. His death had been the subject of controversy when the ambulance took more than an hour to arrive at the East End dive shop to where he was recovered and then left without the body.

    Although witnesses said that the deceased was an experienced diver, Department of Environment deputy director Scott Slaybaugh said the case involved “a series of actions which were significantly hazardous and far beyond the standard of safe diving practices.”

    These included leaving the group to dive alone and ascending rapidly without making the decompression stops mandated by his computer.

    Coroner Eileen Nervik read statements of four witnesses to the case, before the jurors deliberated and came to their verdict of misadventure. (Abridged from the Cayman Compass)

    There’s a feeling of instant camaraderie among the passengers on a liveaboard dive boat because it’s in the interest of everyone on board that nobody has an accident. However, you don’t usually know everyone beforehand, neither do you know their levels of diving skill.

    A diving computer in time-keeping mode. A diving computer in time-keeping mode.

    We will never know what the true circumstances of this tragedy were, but it is likely the casualty did not read or was unable to understand what his computer was telling him. Clear calm water can be seductively dangerous.

    The water at Ras Mohammed, a wall  at the southern tip of Egypt’s Sinai, can be incredibly clear . The water here is said to be around 600 metres deep so you don’t want to drop anything. It’s so clear in fact that you can be misled into going deeper than you intended

    We might have all done that but imagine swimming alongside that steep wall of Shark Reef at 30 metres deep, breathing nitrox 32, and seeing one of your fellow divers in distant perspective way down below you?

    What to do?

    Already the dive had not been going as planned. Our dive guide opted to take the rest of the passengers in another direction and I found that as a former dive guide, I’d somehow been co-opted into leading this small group.

    We had intended to drop in at Shark Reef and swim round to Jolande Reef but the current was intense against us that we were all working hard at making any headway at all. Then suddenly I noticed this member of our group down at great depth.

    The water was so clear I could see that he was wearing a tank marked as containing nitrox just like mine so I took the risk of passing my maximum operating depth and hurtled down as fast as my ears would allow to signal to him to check his computer and follow me back up. He had been at almost twice the operating depth for the gas he was breathing.

    Imagine my horror when only a few minutes later he was back down at more than 50 metres deep, swimming along happily oblivious to the danger he was putting himself in.

    I swam down hurriedly again, thinking that it would be my bad luck if it was me that got an oxygen hit in the process of rescuing this diver who was totally unaware he needed rescuing. Again I signalled in an extremely animated way that he should look at his computer, pointing at his mask and then at my own computer that by now was singing a merry tune thanks to exceeding the maximum PO2 I had previously set on it. It was this moment at which he responded by offering me a naked wrist that indicated he was not wearing a dive computer.

    What an idiot. I was furious and took his arm firmly, dragging him back up to the apparent safety of 20 metres. I didn’t let go of him for the rest of his dive. Where was his buddy? It was his teenage son who’d obviously given up on his father and was swimming above us with two other divers, in the shallows, trying to conserve his air against the hard finning he was doing.

    I was angry to say the least. I kept thinking that this person whom was known to me only because we were on the same liveaboard boat, had forced me to take risks with my own health and seemed oblivious to that fact. On the other hand, had he gone missing it would have ruined the trip for everyone on board.

    Eventually, after a precautionary extra wait at 6 metres (since I had no idea of his dive actual profile and mandatory decompression stop requirements) we broke the surface at which point I emphasised in no uncertain way, “Nigel, if you forget to put on your computer, you must go back to the boat and get it.”

    If your computer was to display this, would you know what it meant? If your computer was to display this, would you know what it meant?

    His reply was unprecedented. He said in a quite matter-of-fact tone, “I decided not to bring my computer because it had stopped working. It went into SOS mode on the previous dive.”

    There are some fabulous new computers available at Ocean Leisure and the staff will be pleased to show them to you. However, they cannot demonstrate the core function of a computer without being underwater with you!

    Please read the instruction manual of your diving computer. Although you may always use it in No-stop diving mode, be aware what the display looks like should it go into Deco-stop mode. It will show a stop depth and either a total ascent time or a stop-time or both at this time. Don’t ignore it. Your computer will help keep you from danger, but only if you’ve read the instructions and fully understand its display.

  • How Do You Store Your Pictures?

    Photographed twenty years ago on Fujichrome film with a Nikonos V camera. Photographed twenty years ago on Fujichrome film with a Nikonos V  camera, digitally scanned and properly stored.

    We spend a fortune travelling across the world to distant diving destinations, recording marvellous images of the marine life we come across. Some of the pictures are irreplaceable.

    In the days of film, when pictures were stored as hard copy, it was easily understood that resulting colour transparencies needed to be stored in a cool dark place with low humidity so that they neither faded nor suffered the onslaught of damp conditions.

    Today, we take thousands more pictures than ever because there is no longer a cost consideration associated with the number of exposures made. Not only that, but the ease with which anyone can achieve satisfying results means that anyone can and will take pictures. Ordinary life has almost become one big photographic shoot-out!

    However, this might become the age of lost pictures. While Lartigue’s collection of photographs were later stumbled across in an attic, how many digital photographs will be conserved in the same way? Digital images are merely a collection of magnetic signals until they are realised on a computer.

    Firstly, you need to store your images in a safe way. Leaving them on the hard drive of your computer is asking for trouble. Computers don’t last forever. Install a new operating system and you risk losing data. You might opt for an off-board hard drive or ‘the cloud’. The cloud is simply someone else’s big computer elsewhere.

    Either way, that’s not enough. You need to back up on to a separate hard drive and if you want to be really safe, you should also back up on to a third hard drive at a different location. Then you must stay alert for new technology replacing what you’re using.

    When I first went over to digital photography, I was concerned to archive my pictures in a secure way. Younger techno-bores in those days told me to save them to CD or DVD. They told me they were guaranteed to last ten years. Ten years? That’s not archival permanence!

    IMG_0604

    If you want to preserve the memories of some of your diving exploits so that you can browse them and reminisce years later, I suggest you take your best shots from each dive trip and construct an analogue book using one of the proprietary programs and services available (iPhoto allows you to do this, for example). You can later take it down  from a book shelf at a moment’s notice.

    These books are beautifully printed and bound and can be organised on your computer in an evening.

    As for you videos, first you must edit them down to a digestible length, using only the best moments of the action you have recorded. If you are using a GoPro camera, there’s a free app (GoPro Studio) from GoPro.com that is easily downloaded and simple to use to do that.

    Then you will have the problem of storage. Luckily, hard drives with several terabytes of space (one terabyte is more than a thousand gigabytes) don’t cost that much nowadays although be aware that the connections to your current computer might change and someone might come up with better technology to replace it. It’s the price we pay for the rapid evolution of this technology.

  • Ethics in Super-Macro Photography

    The on-line-by-subscription newsletter Undercurrent.org recently reported a conflict between winners of the super-macro photography category of the World ShootOut. One contestant alleged that the winner had cheated by herding two commensal shrimp into position on the back of a nudibranch. As a senior journalist on the newsletter, I was tasked with finding a qualified expert to give an opinion on the winning picture but could find none who would be prepared to be drawn on the matter. The judges of the World ShootOut insisted that it was impossible to tell by looking at a single photograph one way or another, yet suspicions remained. However this subject has spawned a bigger issue that may have become important with the massive growth in the popularity of macro photography underwater. There was a time when an underwater photographer may have been an unusual character on a dive boat. In the days of film, it was a difficult and often frustrating activity but nowadays, thanks to digital technology, anyone can go into the water equipped with a camera fitted with a high-powered macro lens and powerful light and record stunning images of the minutia of animal life we have only recently been made aware of.

    A typical high powered macro lens (AOI) that is proving very popular. A typical high powered supplementary macro wet lens (AOI) that is proving very popular.

    This in turn has led to a growth within the diving industry of resorts that specialise in muck-diving. Large numbers of local people who, in the past might have made a living fishing, now work as dive guides and invertebrate-spotters. Every guest diver seems to be armed with a camera of some sort. The problem arises when in their enthusiasm to secure great images, people interfere with nature, moving animals from where they would naturally hide and exposing them to their lenses. Not only that, but they then tend to stay with those subjects for long periods in an attempt to catch the best moment, subjecting these animals to loss of cover in bright light and even damaged habitat.

     

    Halemeda ghost pipefish photographed away from its disguising halemeda algae. Halimeda ghost pipefish photographed away from its disguising halimeda algae.

    Dr. Alex Tattersall, a leading exponent of super-macro photography, is campaigning for better ethics in underwater photography and asking divers to sign a petition, which, I assume, will be presented to those operating muck-diving resorts, magazine publishers and underwater photography competition organisers in the hope of changing behaviour among those using super-macro equipment. His petition (illustrated with one of his own pictures)  reads: “We are seeing more and more manipulation of wildlife to attain award winning images in competitions. Such images are winning competitions and becoming role model for future UW photographers. The UW photography community needs to act responsibly and promote conservation effort. A cultural shift is necessary at all levels and those with influence such as competition organisers and dive magazines should promote more responsible UW photo behaviour.” (If you wish to sign this petition, go to www.change.org and search for “More Ethics in UW photography.”) Some people on social media have even responded to this by suggesting that these animals should be given the choice as to whether they are photographed or not. I suggest that were they capable of making such a choice, they would prefer to remain undisturbed and well-camouflaged where they live, going about their business un-noticed. Seeing a hairy frogfish surrounded by half-a-dozen photographers crowding it and firing their strobes (flashguns) repeatedly can give cause for concern but it is now a daily occurrence where these animals are to be found.

     

    _DSC5057 A dive guide rummages in a gorgonia fan, searching for pygmy seahorses.

    Pygmy seahorses, dug out by willing dive guides with pointer sticks from where they have been hiding unobserved for centuries within the fronds of a gorgonian fan, would probably prefer to maintain their anonymity and certainly prefer not to turn to face a perceived predator such as a big camera lens staring at them. The list goes on. Maybe there should be a rule that no photographer makes more than a few exposures of one subject in order to record its image. Maybe there should be a rule that no underwater photographer stays with one subject for more than a couple of minutes. Some dive centres once tried to ban the use of bright lights by underwater photographers but their loss of business to rival operations soon put an end to that. You may think that concern for the well-being of animals as small as hair lice (animals you would be happy to kill if you found them on the heads of your children) may be trivial in a world where so many bad things are happening. Divers are also concerned about the finning of thousands of sharks, the intentional destruction of reefs in the South China Sea for political reasons, the mass harvesting of sea cucumbers, the unintentional yet effective nevertheless destruction of coral reefs both directly by industry and indirectly by global warming, for example. However, sixty years ago it was thought OK for divers to ride turtles and manta rays and people even thought it was OK to slaughter sharks -  as featured in films by Jacques Cousteau. The maestro of diving even said himself, “Sometimes, for reasons of conservation, it is necessary to use dynamite” which he frequently did. Attitudes change. The mass popularity of extreme macro equipment with today’s underwater photographers may give cause for concern. This is not so much about preserving the life of shrimps but the morality of mankind. I’d like to think that underwater photographers go into the water to record things as they are rather than as they would like them to be. The mass destruction of larger pelagic species by industrialised fishing has left the oceans palpably bereft of fish and those of us who have been divers over a period of thirty years or more can testify to that. Soon there may only be the tiny animals left for us to enjoy. Let’s not spoil it by over-zealous behaviour with our cameras.

     

    Tiger shark lured to the camera with a box of bait. Tiger shark lured to the camera with a box of suitable bait.

    I normally illustrate these blogs with examples of my own photographs but my long career as an underwater photo-journalist has left me with few examples of my own manipulation of small subjects, since I was always briefed to report of what actually happened rather than construct pictures to win competitions, although one could say that seducing a large shark to come close to one’s camera by offering a tidbit to eat is simply manipulation on a larger scale, but sharks can fight back! You may have a view on that.

  • What Causes a Regulator to Free-flow?

    It’s very annoying, isn’t it? You jump into the water and your regulator starts to free-flow. It could even be life-threatening if that happened at depth. It’s as if someone has pushed the purge valve of the regulator in and held it there, losing you precious air. What causes it to happen?Dive2005B

    Modern day regulator manufacturers compete with each other to give the diver the most efficient and natural way of breathing. When you inhale from your regulator, the drop in pressure inside the body of the second-stage of the regulator drops and allows the second-stage valve to open, supplying you with air. Regulator designers try to make the valve as finely balanced as possible so that it takes the minimum amount of effort to pull it open against its closing spring, the spring that holds it shut and stops the gas escaping from your tank. Modern regulators can be so finely balanced in this way that it is often more effort to force the exhaust port open when you exhale than inhaling. (ANSTI breathing machines prove that!) So why do they sometimes free-flow?

    If you pull very gently on a regulator, the second-stage valve only opens a little to let air pass. The more you suck or the deeper you are the more it has to open to satisfy your needs.

    The depth the diver is at affects the pressure-sensing diaphragm. It operates a lever that pulls open the second-stage valve and also doubles as a ‘purge valve’. If for some reason the purge valve gets pushed in for a moment as it might when passing from air at the surface to water (a sudden increase in hydrostatic pressure) the valve opens and lets a whoosh of air past the back of the pressure sensing diaphragm. This fast moving air, just like the air moving fast over the top of an aircraft wing, causes a drop in pressure directly behind the diaphragm. This causes the valve to open even more and – viola! It’s exponential. The more the valve opens the greater the drop of pressure behind it and that leads to it opening the valve even more, resulting in that annoying rush of lost air.

    Luckily, that only normally happens at the cusp between air and water; that is to say at the surface. Putting your thumb over the mouthpiece is usually sufficient to cause a momentary increase in pressure inside the second-stage body to stop it. It’s annoying when it happens at the surface but it could be more than annoying if it happened at depth. Alas, in water that is colder than 10°C, it can happen at any depth if the mechanism of the valve is iced up or affected by ice. This is when it gets more serious than just annoying.

    Why is there ice? When air (or any other gas) is depressurised, it experiences a drop in temperature alongside the drop in pressure. The converse is also true. When a tank has been freshly pumped full, it feels hot to the touch.

    The water you are in may be at 10°C together with the air in your tank but that air in the tank might be as pressurised as much as 200bar. The first-stage drops it down to eight or ten bar more than the pressure of the water it is surrounded by. That’s a huge drop.

    It could easily cause a drop in temperature as much as 20°C and if you are in cold fresh water at 10°C you realise that it equates to minus 10°C for the air passing through the regulator’s first stage. This causes the water in its immediate proximity to freeze.

    Luckily, seawater rarely gets colder than 10°C around our temperate coasts but it’s a fresh water inland sites you might experience this problem – and it can be life threatening.

    You should have been taught how to breathe from a free-flowing regulator on your first diver-training course. The remaining air in your tank will give you time to get to the safety of the surface. Every diver should know how to do that.

    If you are in the habit of diving at inland sites, get a regulator designed for the job. They usually have first-stages that are environmentally sealed, with no working part coming into contact with the water, and they include extra metal to act as a heat sink to transfer what little warmth there might be in the water to the much colder air coming from the tank. Ask about that when you next buy a regulator. Ocean Leisure stocks cold water approved regulators by both Apeks and Scubapro.

  • Dome Ports for Underwater Cameras

    Serious underwater photographers shoot their wide-angle pictures from behind dome ports. What’s that all about?nauticam4.33domeport

    A dome port has no effect when viewing through it with the same medium (air) on both sides but once you put the outer surface in contact with water the refraction between that and the air in front of the camera lens comes into play. What happens is that a virtual image is formed ahead of the dome port and the camera lens is allowed to focus on that instead of the real subject some distance ahead. The effect is to produce an image that is more saturated in colour. The problem comes when you realise that this virtual image is curved and the distance in front of the lens is quite close.

    Some photographers get disappointed when they find that their expensive wide-angle lenses are no longer giving images that are sharp from side to side and resort to fitting them with high-strength dioptre close-up lenses in order to get them to focus close enough to get this virtual image sharp.

    That’s because most expensive wide-angle lenses are rectilinear designs that have a very flat field-of-view, something that is admirable when using them solely in the medium of air. At the same time, few focus close enough.

    That’s why you’ll see top underwater photographers using full-frame fish-eye lenses behind dome ports. Often these give very disappointing results in air but in conjunction with a dome port their aberrations actually become an advantage. A curved field-of-focus is a positive bonus where trying to make a sharp record of a curved virtual image.

    Dome ports come in different diameters with a different radius to their curve. The bigger the dome port the further in front of it the virtual image is formed and the easier it is to get the camera lens positioned at the right point behind it. That said, big dome ports can be unwieldy to use, hence the popularity of mini-domes. The smaller domes produce their virtual image much closer to the front of the port and it’s really important that the front node of the lens is positioned in the correct place relative to it.

    The front node is not something you can see. It’s an optical term. Camera housing manufacturers have done empirical tests with most popular lenses to confirm what spacer ring might be needed to allow the dome to be positioned in the right place relative to the camera. They provide lens/port charts for this purpose and your underwater photography equipment dealer will have that information if you cannot find it on-line.9inchzendome

    Dome ports can be made of acrylic material, polycarbonate or glass. Glass is the most expensive and the most hard wearing but if you are unlucky enough to scratch or chip it, there is nothing you can do apart from clone out the unwanted mark in your pictures, later with software on your computer.

    Polycarbonate is inexpensive and lightweight but the same applies as glass should you damage it. Acrylic ports have an advantage in that the material has the same refractive index as water so minor scratches become invisible in your shots underwater unless you happen to take a picture into the sun. Acrylic is very easily scratched but in the same way it is very easily polished.

    Simply take a piece of fine grade abrasive as used in finishing the paintwork of cars and gently cut back the scratch until they are has become an evenly matte surface. Then polish it back to clear acrylic using some proprietary silver polish wadding. It takes some elbow grease but you will be rewarded with a dome port that is immaculately clear of marks.

    Some say that glass ports are optically superior to acrylic ports. I have owned and used both including an optically coated glass port that I imported specially from Japan and can tell you that the pictures taken with both this and a top quality acrylic dome are indistinguishable.

    A manufacturer like AOI makes a range of glass and acrylic dome ports for Olympus system compact camera housings so the choice is yours.

    You may find that a large glass port is easier to use for those over-and-under shots taken at the surface because droplets of water are less likely to cling to the glass. A large dome port certainly helps get those type of pictures because, remember, the lens has to focus on a nearby virtual image for the under part and the over part is in air, probably at infinity. You need to use very small lens apertures to get the huge depth-of-field needed or a split close-up lens that affects only the bottom part of the lens. These rarely fit on fish-eye lenses.

    Some underwater photographers report good results using smaller domes for these over-and-under pictures but invariably they are in bright sunshine that allows them to use the smallest lens aperture with perfectly calm water, but they normally need to make an exposure adjustment in digital post-processing to get both halves of the picture in balance.

    The important thing to remember is that when buying a port, you will need the right extension ring to position it correctly relative to the lens. Alas, it’s not something you can confirm by taking a picture when in the equipment sales room and not underwater.977685_632320780114194_1262934048_o

  • What’s Better? DIN or A-clamp?

    The international A-clamp fitting enabling a regulator to be connected to a tank was once ubiquitous at diving centres worldwide, but recently the German DIN fitting appears to becoming more popular. When it comes to buying a new regulator, the choice is yours but which is best?

    mikron_blue_yokeAs usual there will be those that show unswerving loyalty to one type or the other and robustly defend their choice, but the truth is that both systems have advantages and disadvantages.

    The A-clamp uses an O-ring fitted to the tank and the regulator is clamped to it. These O-rings can get damaged in normal use especially in a busy tank rental situation so it’s a very good idea to inspect it before you connect up and go diving. Wise divers carry a few spares just in case and are aware in different parts of the world these O-rings can vary slightly in size. However, a good O-ring combined with a properly mounted regulator first-stage can give trouble-free service for the ordinary single-tank diver. That said, you’d often see divers with fine bubbles escaping from the interface between regulator and tank valve thanks to a worn tank O-ring.

    You’ll also hear stories of A-clamps coming mysteriously undone. It’s an urban myth. Once the tank valve is open the internal gas pressure makes it impossible to disconnect just as with a DIN valve.

    mikron_pink_dinThe regulator with a DIN fitting carries its own captive O-ring. These too can wear but, not subject to the vagaries of many different size regulators being hooked up to them, they wear a lot less than the easily replaceable O-ring on a standard A-clamp tank.

    Not only that but without the complexity of the clamp, the DIN regulator has a lot less metal and is on consequence lighter. It is screwed directly into the thread of the DIN tank valve where the O-ring makes contact internally at the back. On the face of it, the DIN fitting is a better solution.

    Part of what is driving the popularity of DIN-fitting regulators is technical diving. When using a cluster of tanks, a cluster of A-clamps can be an entanglement issue. Not only that but you can get DIN tanks and suitable regulators with longer threaded section to be used with much higher tank pressures than 3000psi, providing more gas in a similar size tank. (Be aware you cannot use a standard DIN connection in one of these high-pressure tank valves although you can use a high-pressure DIN fitting regulator on a standard DIN tank.)din_tank

    Most DIN fitting tanks at dive centers outside the American sphere of influence have a little slug that can be inserted so that they can be used with most A-clamp fitting regulators as well. Clever divers always carry one of these slugs with them if they have an A-clamp regulator but where DIN tank valves are more popular. din_insertOn the other hand, many dive centers in the USA and Caribbean areas often only have standard A-clamp tanks so that those with DIN regulators must fit a bulky A-clamp adaptor, something that pushes the regulator a little further forward and can prove uncomfortable at the back of the head.apeks_din_yoke_converter

    There are a couple of disadvantages of the DIN system, which exponents tend to gloss over. Firstly, those with weaker fingers find them difficult to screw up tightly or unscrew especially if hands are cold or the diver has long manicured nails. Be aware too that regulations in Europe stipulate that nitrox tanks and regulators require a different DIN thread size to that of tanks intended for use with air (but NOT in the UK).

    yoke_tankAnother is that tank valves are usually of brass and if rough handling deforms the tank valve even slightly, it can prove impossible to fit a regulator. That’s probably why busy dive centres in the USA and nearby prefer the more robust A-clamp-only tank valve design.

  • An Intro to Diving Computers

    When we go under pressure, our bodies start to absorb the inert part of the air we breathe, the nitrogen. At normal atmospheric pressure we are saturated with nitrogen but by going underwater breathing compressed air, we allow our bodies to soak up more.

    Provided we stay no longer at depth than a slow ascent to the surface can give time for our bodies to off gas, we experience no problems. If we exceed these ‘no-stop’ times, we need to make stops at points during the ascent to allow our bodies to ‘catch up’ with this process.

    An advanced computer watch A typical computer watch

    All certified divers should know this and nowadays most wear a computer to monitor the potential state of decompression during and after each dive. I say ‘most’ because I have recently heard of cases of individual divers who eschew a computer saying ‘they know how deep and for how long they can stay’. This is very dangerous thinking.

    Of course, many years ago when computers were in their infancy, conservative divers refused to use them, believing a watch and depth-gauge combined with a decompression table was safer. They might have been safe if their watches and depth-gauges were accurate and they were disciplined in their use.

    One way to make leisure diving ‘safer’ in this regard is to breathe a gas with less nitrogen in the mix – nitrox – but it is only safer if you don’t take advantage of the longer no-stop times available. Stay longer and you still soak up just as much nitrogen as you would breathing air for the shorter no-stop time mandated.

    Computer manufacturers try to make things as safe as possible to keep them away from possible litigation. That’s why they build in a few precautions that sometimes casual users fail to comprehend.

    suuntodx_elastomerIf you dive with your computer set in ‘air’ mode, it will not allow you to switch to another mode such as ‘nitrox’ until a sufficient period has passed – usually twenty-four hours. If you want to switch between air and nitrox, it’s important to start off in nitrox mode, setting air as nitrox 21 (which it is).

    For the same reason, if you want to use your computer simply in ‘gauge’ mode, reading only depth and time, it will not be able to calculate your residual nitrogen levels should you wish to then switch to a nitrox or air diving mode, so it will lock you out for a period, up to forty-eight hours if you have been diving deep.

    Diving computers have a sampling rate typically of every 10, 20 or 40 seconds. Normally the 20-second setting is the default setting. During a leisurely dive this is entirely practical but it is not suitable for free-diving.

    Some computers have a mode specifically for free-diving when the sampling rate is much more often, even every second. This is because if you swim down to, say, 20-metres deep, a less frequent sampling rate might make a sample point at ten-metres on the way down and the next at 15-metres on the way up, totally missing the fact that you went to 20-metres in between. So gauge mode is unsuitable for use by free divers. You may need a computer with a ‘free-diving’ mode. Choose a computer that has the modes you require.

    Some of our customers tell us they want to free-dive between scuba dives. Current medical thinking believes this to add a degree of hazard to the activities because the scuba diver’s body will still be loaded with residual nitrogen at this time and that will be recompressed during a breath-hold dive. No computer can calculate for these short bounces while in diving mode because of the aforementioned sampling rates. For this reason, no computer should allow you to switch to free-diving mode while it is still calculating nitrogen levels during a surface interval.

    Some foolish divers will leave their computer to ‘off-gas’ at the surface while they go for a swim, ever tempted to duck-dive below the surface. That is a silly as leaving a computer tied off to a rope at the last decompression stop to ‘offgas’ while the diver climbs back on board. We positively do not recommend this. Nor do we suggest you buy a second instrument and switch between them during a day’s diving. That is the road to decompression illness.

    A diving computer can only monitor the nitrogen loading of your body if it is attached to you while you on-gas and off-gas. Use it properly and it will keep you safe – although, since everyone is physiologically different and the computer’s algorithm was written for a theoretically typical person, no computer manufacturer can guarantee this.

    Always read the instruction manual and be familiar with what you computer displays. Too often people go into decompression status during dives, especially where the water is warm and clear, and fail to understand that this is what their computer is telling them.

    A range of different computer displays at depth A range of different computer displays at depth

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