A MASK is a very personal piece of equipment. If it fits your face, does not perpetually leak, and you can see clearly, you will probably find none better.

A mask with a wide face-plate does not give you a wider angle of view than a
low-volume mask where your eyes are positioned closer to the lenses. To argue this would be like arguing that a bay window gives you a better view of the street than sitting close to a smaller window.

Low-volume masks can make the wearer look a bit like Batman, but they tend to leak less water than large-volume varieties. They hold less buoyant air so there are fewer forces at work to cause a mask's skirt to flex at the face. They also tend to be easier to clear, because they hold less water when flooded. However, if you want a large-volume mask that clears easily, some have purge valves built into the nose area, such as the Zeagle Beta, Tusa 8000 and Oceanpro Fidji.

Photographers often prefer their underwater models to wear masks with a large face-plate, but this has more to do with how they look than how they look at things! The Mares Vedo is one of the few masks of this type still available.

When trying on a mask, offer it up to your face and inhale through your nose. The mask should suck onto your face and stay there without the aid of a strap for as long as you can hold your breath. If you have a face of child-like dimensions, some makers produce a narrower product - for example, the Typhoon Phoenix.

Because water is more dense than air, light refracts as it passes from the water to the air within a mask. This makes things look closer underwater, and it narrows your angle of vision. No manufacturer has managed to solve this problem. The Oceanic Bi-Vu mask includes prisms in the bottom of the lenses which make it easier to look down at the equipment you are wearing.

The old-style rubber skirts have been largely superseded by silicone. In its most popular form this is transparent, which, contrary to what the ads may say, does not make it easier to see behind you. Photographers prefer to use a mask with a black silicone skirt to avoid any confusing reflections on the inner surface of the glass. Trendy tekkies also prefer masks with black or opaque silver/grey silicone skirts, such as that used by Zeagle.

A wide variety of masks is available in dive shops priced from as little as £12 to around £80. Most seem to come from the great mask mine in Taiwan, interspersed with a few from Italy and America. They have either a single plate of glass or two individual lenses, which gives you the option of fitting prescription lenses if needed.

Many manufacturers can offer lenses for short-sighted people off the shelf - for example the Technisub Look, Oceanic Customeyes, Tusa Liberator Plus, Sherwood Genesis and Mares Seta. There is also the option to have prescription lenses moulded onto any two lense mask, at an extra cost of around £45.

Because glass used in a mask must have a minimum thickness, positive dioptre lenses present a few engineering problems to the mask-maker - you could end up with lenses resembling the bottom of a beer bottle. However, there are opticians who can fix positive lenses to the inside of plain masks.

Some masks have multi-lens designs which, in their most complex form, can make you feel like you are looking out at your dive through a small greenhouse. With the Mares ESA you could, if needed, have thick positive lenses in the lower sections, and negative sections in the upper sections.

When masks are made, silicone tends to contaminate the glass, causing it to steam up. Technisub can supply a mask with mist-inhibiting glass (MIG). Otherwise you need to clean the inner glass before you use the mask for the first time by rubbing it gently with a very fine abrasive medium. Traditional toothpaste is ideal for this - use a pea-sized nodule and rub it around until your finger starts to get sore. Be sure to rinse away any traces of toothpaste afterwards or you will be looking at the underwater world through a sea of foam.

The full-face mask used to be confined to the province of professional divers - those compelled to dive in places that would be our last choice of dive site! Water polluted by sewage, toxic chemicals or worse demands equipment to keep the diver safe from harm.

The price of a professional mask reflects that fact but it is inevitable that examples priced for the leisure diving market will become available. The Ocean Reef mask is among the first.

A full-face mask needs some additional training in its use but it is undeniable that it can add a degree of comfort during those familiar winter inland-water dives. For tekkies who might need to switch gases under water, a full-face mask with a gas-switching block can eliminate the need to drop one mouthpiece while looking for another.