Q: I need glasses and I can't see an LCD screen properly without them. What do I do underwater?

See the LCD Magnifier article.

Q: I want to buy an underwater camera as a present for someone else. What should I get?

A: The problem is that you need to have a good understanding of your friend's requirements and level of attainment before you can make a good decision. You should also be minful of the fact that people who own or use computers usually have no interest whatsoever in film cameras; so in this case a digital camera is mandatory, and you need to make sure that the computer which will be used to download the pictures has a USB port and that its Operating System can run the camera software (Microsoft Windows is a safe bet). If the computer is favourable; small digital cameras from the main manufacturers, with their companion 40m polycarbonate housings, make nice 'self-contained' presents; being self-contained in the sense that they don't require the recipient to aquire a whole lot of extra equipment before they can be used. Make sure that the camera-housing combination you choose allows the internal flash to be used; that is, unless you also want to master the complexities of underwater lighting and choose a flash system at the same time.

Q: How can I take good underwater photographs without spending large amounts of money?

A: Most high-end underwater camera equipment is expensive because the market for it is small, which means that the end user must pay a significant proportion of the development cost, and the expected return does not always warrant a high degree of automation in manufacturing. There is also a premium on solving the technical problems posed, particularly in matters to do with lighting, optics, and waterproof enclosures. Keeping the cost down involves compromises. One solution is to opt for restricted depth; in which case you can put a compact camera or an SLR into a ewa-marine flexible housing. Splashproof and shallow water housings are also a possibility, but most are designed for surface watersports, and are often unable to withstand significant water pressure. For general SCUBA diving, a pressure resistant casing is required; and the lowest cost solution is usually one of the 40m polycarbonate housings marketed by the mainstream camera manufacturers (Olympus, Canon, Sony, Nikon, Pentax, Fuji and Casio). Good points to look for, even in inexpensive equipment, are the facility to fit close-up and wide-angle adapters, and provision for an external flash unit. You can use built-in flash in very clear waters, but backscatter from suspended particles is a serious problem in conditions of moderate visibility.

Q: Can I avoid buying an underwater camera by hiring one whenever I need one?

A: Yes, but hiring is likely to be expensive. You can sometimes hire cameras at holiday resorts, but if you do so more than a few times you can end up paying more than the cost of the equipment. Hiring from a professional agency is always expensive because the equipment must be serviced and pressure-tested prior to release. You may have to pay the repair costs if you accidentally flood the equipment. Not also, that you cannot expect to produce top class results using unfamiliar equipment.

Q: Should I borrow or lend camera equipment?

A: So whose fault is it if something goes wrong? The borrower can argue that the problem was due to cumulative wear and tear, and the lender can argue that it wasn't. Most flooding incidents are due to inexperience and bad O-ring maintenance; making borrowed cameras particularly vulnerable. Say no politely; unless the borrower is an UW photography guru, in which case, extract a deposit.

Q: I want the best possible equipment; what should I consider?

A: Water is an optically dense medium, which means that it absorbs light of all colours, not just red. Water is also usually cloudy to some degree, even in the tropics. The upshot is that all technically good photographs (sharp definition, high colour saturation) are taken from very short range, and nearly always require flash. In addition, best suppression of backscatter is achieved by aiming the camera and flash from different directions. The best general-purpose camera system is therefore one which allows you to use high quality macro, close-up, and close-focusing wide-angle lenses, and which allows you to use one or more external flash units (preferably with TTL exposure control or variable light output).

If your interest in underwater photography is professional, or you have a very large budget and considerable experience as a diver and photographer; the pertinent issue is that the ultimate image quality attainable from a camera system, for a given number of pixels, is a function of the format (the dimensions of the imaging area or film frame). The reason is that a larger format permits a longer focal length of the lens for a given angle of coverage; and the aperture size of the lens, for a given illuminating power, is a function of the focal length. When correctly stated, an aperture value should be written as " f/n " (focal length divided by a number). Now, if we consider a 50mm lens operated at say f/16, the diameter of the aperture is 50/16 = 3.125mm. If we use a small format digital (compact) camera, we might need to use a lens with a focal length of about 10mm to get the same view as would be obtained with a 50mm (normal perspective) lens on the 35mm (36 x 24mm) format. The 10mm lens operated at f/16 however will have an aperture diameter of 10/16 = 0.625mm. This places it at a disadvantage compared to the larger format camera, because light undergoes a process known as diffraction when it interacts with structures of comparable size to its wavelength. Diffraction causes the light to spread out when it encounters obstructions, and the result is a loss of resolution (sharpness) in photographic images. Diffraction is the reason why lenses do not give progressively more resolution as the aperture size is reduced, they give instead a peak in resolution at intermediate apertures, and lose resolution progressively as the aperture becomes smaller. The point is that, for a given field of view, a small format camera with its short focal-length lens will start to suffer from loss of resolution due to diffraction at a wider relative aperture than a large format camera with its long focal-length lens, i.e., while both cameras might be operating at the same relative aperture, say f/16, the small format camera will have a physical aperture of (say) 0.6mm, while the large format camera will have a physical aperture of 3.1mm. In fact, the diffraction problem is sufficiently pronounced with small-format compact cameras that most cannot be used at apertures smaller than f/8 (the option is simply not provided), whereas 35mm format, and near-35mm format digital cameras can be used at apertures as small as f/22 or even f/32 with suitable lenses.

The upshot of the argument given above is that the best general-purpose digital cameras have image sensors approaching the size of the old 35mm (36 x 24mm) film format. This means, given the current state of the art, that the professional photographer should opt for a digital SLR camera, even though the continued use of mechanical reflex viewing apparatus (the mirror actuator) is somewhat questionable (a digital camera with a video screen is a single-lens reflex camera). Having chosen a dSLR however, it is important to understand that best results will not necessarily be obtained by using old lenses designed for 35mm film. Old-design macro, portait, and telephoto lenses are fine; but wide-angle lenses and short zooms need to be designed specially with digital sensors in mind. The problem is that the light sensitive areas of the camera sensor are sunk into wells (depressions) in the silicon, and the incoming light is usually separated into its red, green, and blue components by means of an mosaic of filters just in front of the sensor layer (other sensor architectures are possible, but similar arguments apply). All of this means that the sensor will show a strong fall-off in sensitivity for light arriving at oblique angles. The solution is to design a wide-angle or zoom lens to have its exit pupil much further away from the sensor than was the practice in the days of film. Such lenses are called 'Telecentric' lenses, but may also be described as 'optimised for digital cameras', etc.

So, to summarise, the camera should have a large sensor area (20mm diagonal or larger), and for wide-angle photography, should be used with telecentric lenses. The sensor should also have a large number of pixels of course (see pixels article for an explanation of the issues). Once these requirements are understood, it becomes a matter of finding a housing which will accommodate such a camera, and then following traditional underwater photography practices: i.e., using flat ports for macro photography, and dome ports for wide-angle photography. To get the best possible photographs, there is then only one issue which remains, which is the matter of correcting for the effects of the air-water boundary.

Water has slightly different refractive indeces for red, green, and blue light, and so any air-water boundary (i.e., port) will introduce chromatic aberration (colour fringing in off-centre detail). In the long-forgotten days of film photography, Nikon made water-corrected lenses for its Nikonos camera system, but no such lenses exist for modern cameras. It transpires however, that the lack of water corrected lenses is not a problem, because software can be used to remove chromatic aberration after the photograph has been taken (see the software lens correction article for details).

Q: Do I need different equipment for different parts of the world?

A:
1) Cameras with built-in flash give poor results in conditions of moderate to low visibility.

2) A well appointed UW photography system can be used in just about any location; the problem is rather that of guessing which lens configuration to take with you when you're only going to get one chance to visit a particular site. If you fit a fabulous wide-angle lens and a dome port to your housing, you may regret the decision if the visibility turns out to be awful or the small marine creatures turn out to be interesting. If you fit a close-up lens to the front of the camera (room in the port permitting), you may regret it if you experience a sudden infestation of large marine creatures. The best solution to this 'tourist's dilemma' is to choose a system which can accept supplementary lenses on the outside of the standard lens port. Many digital compact camera housings have this facility, often in the form of a 67mm filter ring, or via an adapter which can be fitted to the port, so that screw-in or bayonet-fitting wide-angle and macro lenses can be fitted underwater as needed. There is still some mileage in owning a dome port if one is available, because the dome will give better optical quality than a supplementary wide lens for situations where you know that the visibility will be good, but nothing can match the versitility provided by lenses which are interchangeable underwater.

3) If you intend to use underwater colour correction (UWCC) filters, note that there are two types: UWCC-G for green waters, and UWCC-B for blue waters. The green bias in some locations (e.g., Mediterranean and parts of the UK) is due to algae suspended in the water.

Q: Does the warranty (guarantee) on a housing cover the equipment which goes in it?

A: No. A standard warranty covers defects in the materials and workmanship involved in making the product. It does not cover the risks of collateral damage and consequential loss (e.g., failure to complete a photographic assignment), for which you need insurance.

Q: If I buy an underwater camera system, will it hold its value?

A: Any item purchased new loses value at the instant of purchase becauses it changes from being new to being secondhand (and the warranty is not necessarily transferrable - it depends on the country of purchase*). Consequently, you are unlikely to get more than 2/3 of the initial purchase price by private sale, and you will get 50% of the initial price or less if you sell to a dealer (it depends on condition, and resale potential), and this only applies if the equipment in question is still being manufactured. Camera specific housings in particular do not hold their value once the model has been superceded, and the current situation is that there is very little demand for film camera equipment. There is even less demand for equipment with scratched or damaged optical surfaces, siezed screw-threads, and battered bodywork, and so it follows that for equipment to retain its maximum value it must be used carefully and washed and maintained correctly.

* In the UK, the Guarantee is part of the contract between the seller and the purchaser. The retailer is not subject to contracts to which it did not agree; and so the original warranty evaporates when the customer sells the equipment to someone else. The selling point "still under warranty" is therefore a mis-representation in secondhand sales from private individuals in the UK (and also in many other countries). Secondhand sales from dealers are usually accompanied by a newly created warranty, underwritten by the dealer, not backed-up by the manufacturer (and therefore usually restricted in its scope).