dome ports

  • 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

  • How to Get Clear Sharp Pictures Underwater

    VerdeIsland5191There are some basic rules to getting clear sharp pictures, whether it be video or stills, while under water because it is the water that ruins so many good photographic opportunities. Firstly, the clearest water is not clear. Well, it's not as clear as clear air might be. If you could eliminate the water, think how much clearer your pictures would be!

    How do we do that? Simply by getting as close to your subject as possible and thereby eliminating as much water as you can between your camera's lens and your subject. That's why inexperienced underwater photographers have most success initially photographing macro subjects. Because they are small, it's easy to get the camera up close and personal to them. You only need to enable the camera to focus on them. Those with top-of-the-range DSLR cameras can equip themselves with a macro lens specifically designed to focus very closely. The lens merely needs to be installed behind a flat lens port or 'macro' port. Those with cameras that have a fixed lens (such as most compact cameras) will need to fit and auxiliary macro lens to the outside of their housing. The same can be said for GoPro POV cameras._DSC5564

    But what about bigger subjects? That's where a wide-angle lens comes into play. Again, a DSLR user will need to fit such a lens and mount it on the camera behind a suitable dome port. Dome ports produce a virtual image just ahead of the camera so you must be sure your choice of lens will focus close enough on that. The advantage is that a dome port keeps the angle-of-view the same for the lens as it would be if used in air. Wide-angle lenses are not used to 'get more in' but to allow the photographer to move closer without 'cutting more out'.

    Again, compact camera users will need to fit an auxiliary wide-angle lens to the outside of their housing. There is a variety of choices but you should be advised by an expert as to which will suit the fixed lens of your camera if it is not to vignette the photographs. The advantage of fitting lenses to the outside of the housing is that these wet lenses, whether macro or wide-angle, can be interchanged at will, whilst submerged.

    Water has another property that makes the life of an underwater photographer a little complex. It absorbs light so that as you go deeper it gets darker, but it also absorbs light selectively. The longer wavelengths of light (red and green) get soaked up first so that very soon, at a depth of no more than a few metres, everything will look blue in your pictures. What can you do about that?_DSC8326

    One way to look at it is to see it as a surplus of blue light and if you can reduce the amount of blue light you will allow the camera to make the most of the red and green light that still penetrates the water to the depth you are at. Some cameras allow you to "White balance" and provided the software designer has provided enough range to account for the excess of blue light, this can be very effective. It's best to point your camera at something neutrally grey to do this. A piece of white Perspex is ideal but failing that, the palm of your hand underwater can usually be good enough. Canon compacts are especially good at white-balancing against an excess of blue. Sadly for underwater photographers most software designers are thinking in terms of white-balancing against incandescent light, which tends to have an excess of red and green but those who work for Canon seem to have it nailed.

    Of course, some cameras do not have the facility to white balance, so what then? A red filter will make the most of what red light is present but of course you will need different degrees of red according to the depth you are at. You can fit alternate filters to a GoPro camera or you can fit a Backscatter Flip Filter 3.1 system. This gives you the option to flip the appropriately coloured filter in front of the lens and make a judgement by looking at the image on the LCD screen. If you have a Hero 4 Black or an earlier GoPro 3 you can fit an LCD back available as an accessory.

    A better way to get good colour in your pictures is to take some white light with you. In the case of video a constant light source is necessary and can vary in price from a basic Big Blue rig to something more ambitious. You cannot have too much light but it needs to be of the right colour and exceedingly even in its spread, or your video camera will try to look into the shadows and the lit areas will burn out. You will need a lot of light to get good still photographs even for macro subjects when the light source is very close indeed. Even a high-output Keldan light has a limited range. For good still pictures there is no substitute for an underwater strobe or even a pair of them. They emit a quick burst of light but it is many times brighter for that short duration than any constant light source. These can vary in price from the Sea & Sea YS-03 and Inon S2000 to the bigger hitters like the Sea & Sea YS-D2._FFF7119

    Professional underwater photographers shoot RAW files and there is a very good reason why they do this. RAW files allow you to do a lot of adjustments to your pictures after you have been under water when there might have been time constraints. Many compact cameras can shoot RAW files but because these files can be very large it can mean a significant delay of a few seconds between taking pictures. DSLR cameras have buffers of varying size that allow users to shoot a lot of RAW files without this annoyance. Depending on what you are photographing, the delay between shots might be worthwhile. Next week we'll show you the advantages of adjusting files from a RAW original long after the event.

  • The Amazing Rhinopias

    _DSC8312 Rhinpoias Aphanes or Lacy Scorpionfish
    The Lacy Scorpion fish or Rhinopias Aphanes is found in the waters of Papua New Guinea and West Papua. Unlike a lot of colourful marine life, you don't need a macro set-up to get good pictures if you come across one because they can be up to 25cm in length. They are a benthic species in that they tend to rest on things rather than swim. However they often get about by hopping around on their pelvic and pectoral fins. Despite they fact that they appears to be very colourful in these photographs they are masters of disguise and although they often pose precociously atop sponges and coral heads, you can easily pass one by because under natural daylight they are quite hard to see. They were first brought to the attention of marine scientists by British/Australian diving pioneer Bob Halstead who after a career as a schoolmaster took to running scuba diving expeditions and later skippering his boat mv.Telita, taking divers on scuba diving charters around the waters of the Coral Sea, embarking his passengers at Port Moresby. Among other things, Bob Halstead has written several books on diving around PNG.
    Lacy Sorpionfish or Rhinopias Lacy Scorpionfish or Rhinopias Eschmeyeri
    After he started noticing these flamboyant fishes he sent some pictures that he'd taken to experts at the Natural History Museum in London who confirmed it was a previously undescribed species. In fact there are several sub-species. Bob is known for his insightful analysis of diving practises and also for his humour. One of his most well-remembered quotes is: "If you can't take a joke, don't take up underwater photography!" The first time I visited PNG I made it my business to photograph some examples of this keynote fish but after a lot of searching and no luck came back with an article for UK's Diver Magazine entitled 'The Rhinopias is Missing!' I kept my sense of humour. The next time I stayed at the Loloata, a resort on its own island in Bootless Bay run by Australian Dik Knight, the dive guides made it a matter of honour that they did not fail to find me an example to photograph. They took me to a reef called Dinah's Delight, named after Bob Halstead's first wife, also an accomplished scuba diver in her own right and it was if all the Rhinopias in various different sub-species had come out on parade. _DSC8421   To photograph these wonderful looking fish you need a a wide-angle lens so that you can get as close as possible and an underwater flashgun or strobe so that you can reveal them in their full spectrum of colour. The other things you will certainly ned is a pair of sharp eyes and a lot of patience whilst looking for them because in natural daylight they easily merge with their background.._DSC8406 One last point: Rhinopias are said to be the Holy Grail of marine aquarists who like nothing better than to keep one in an aquarium because these delicately coloured fishes are so pretty. Let's keep them in the ocean where they belong. (The pictures here were all taken with fish-eye lenses behind dome ports and with ancillary off-camera flashguns.)

  • The Physics of Underwater Photography

    _FFF8337 The rules of physics apply to all underwater photographers. Get close!
    When it comes to water everyone realises that to get your camera wet spells disaster. It’s either got to be designed to be waterproof or it must be enclosed in a waterproof housing. Water pressure is such that at only ten-metres deep it’s twice air pressure at the surface and much more as you go deeper so designers of housings take that into account. However, there is much more to underwater photography than simply keeping the camera dry and the same rules apply even if you have the very best kit. Photography is all about light and light acts in a different way in water to the way it does in air. For a start, water is never as clear as air. If you had 30-metres of visibility under water it would seem gin-clear yet the same visibility on a motorway would see you driving very slowly. It’s all about turbidity. Water is full of detritus and tiny life-forms. The secret to getting clear sharp pictures is to reduce the amount of water between your camera and your subject, to get as close as possible.
    Daylight is naturally filtered blue by the water.
    Water also absorbs light but it absorbs light selectively. The longer wavelengths of light, the reds and the greens, get filtered out within only a few metres from the surface so that the brightest daylight looks blue under water. You can make the most of what red and green light gets through by filtering out some of the blue with a reddish filter or by repeatedly white-balancing your camera as you find yourself at different depths. You can take some portable white light with you in the form of an underwater flashgun (or strobe light) for stills or a bright video light for movies. However, remember that the light from these is affected in the same way and the range of such accessories is limited, possibly to less than two metres, so you still need to get close to your subject.
    LibertyWreck An independent flashgun or video light will give good colour to closer subjects.
    At the same time you need to position these lights well away from the camera’s lens axis or they will simply light up all that detritus in the water and give you a very messy result. We call it ‘backscatter’. Mounting a flash or light on the end of an accessory arm does the trick but for convenience sake we normally have this attached to the camera housing via a suitable tray and manipulate the light via a series of one-inch ball joints and clamps. Ocean Leisure Cameras stocks a vast array of these to solve every mounting problem whether it be for a GoPro, for a top-of-the-range DSLR camera rig, or for something in between. Light is refracted when it passes from water into air through a flat glass camera front so that things appear at least one-third closer. It effectively makes your standard camera lens slightly telephoto. So having got close to our subject, we might find that we cannot include all of it in the shot. This is where a wide-angle lens comes into play. Under water, wide-angle lenses are used differently to the way they are used on land. They allow the camera to come close to the subject with the minimum of water between them, while at the same time restoring the image size.
    Bantin62-63-2 A wide-angle lens enables close positioning to larger subjects.
    A dome port combined with a wide-angle lens or a compact camera’s zoom lens at its widest setting will restore the angle of view by reducing the amount of light refraction. These are available to fit some compact camera housings as well as housings for cameras with interchangeable lenses.
    _DSC3408 Macro photography is a good place to start,
    Many underwater photographers start off by concentrating on macro subjects. A macro lens allows you to get very close indeed to the smallest of subjects and by using a flashgun on a mounting-arm, you take in with you your own ready-made mini studio set-up. Good results are assured because as your lens gets very close there is so little water to contend with. Flat housing ports help in this case because the refraction of light helps you stand off from your subject so that you can light it more easily. In summary, you need to prevent water ingress to your camera, you need to make the most of the full spectrum of natural light that penetrates the water, you need to avoid lighting up the turbidity of the water and, by getting as close as possible to your subject, you can reduce the effects of the poor optical quality of the water. The people working at Ocean Leisure Cameras can provide you with everything you need to achieve that. You just need to perfect your diving skills so that they become second nature while you take pictures or record video.

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