That said, these sensors are generally still half the size of a 35mm frame of film, so lenses have to be of shorter focal length to give the same angle of view as the 35mm equivalent.
Why not make the sensors as big as a full frame of film? It's possible, but as sensors get bigger they get exponentially more expensive. Producing a full-frame (FX) camera costs a bomb.
I've been getting stupendously high-quality results with my DX Nikons, but I was seduced into getting a full-frame FX Nikon D700, because it can use all the Nikon lenses I have collected since 1970, and can be used at very high light-sensitivity settings (such as 1600 ISO instead of, say, 200 ISO) without any digital noise or grain showing. Well, thats the excuse I gave my wife.
Every underwater photographer has flooded a camera and lens. I've done it more than once. After flooding my first DSLR, I was so scarred that I would never risk putting my then very expensive DX Nikon D2x in a housing.
The guys at Hugyfot have convinced me otherwise, because theyve done away with that business of sealing your beloved camera into its housing and hoping it doesnt drown when you dunk it. The Hugycheck system I reviewed recently (divEr Tests, February) tests the seal by reducing pressure inside the housing and seeking out leaks using non-damaging air rather than destructive water.
It convinced me. I dived into what Gordon Brown had left of my pension fund for £2500 to buy a Nikon D700 and 16mm Nikon fish-eye lens. (By the time you read this, both will probably be obsolete!)
Superficially, the D700 looks much like my previous D200 (and the D300 that replaced it) except that it has an even more marvellous focusing system, and needs longer focal-length lenses.
The 16mm Fish-eye on the FX is much like the 10mm Fish-eye on the DX I had been using, but all my old lenses work seamlessly (auto-focus apart, for the manual ones) and I have a huge choice of prime lenses (from 20m to 105mm) available for surface use or underwater macro photography.
Unlike many FX cameras, this is not a bulky beast, and any housing for it is only a centimetre or so taller, so this will prove a popular choice of full-frame camera with underwater photographers.
What matters is that I can habitually use small lens apertures and high shutter speeds, or use my flashguns on a one-eighth power setting, so battery charge lasts a lot longer.
I can get more than 200 RAW files recorded on a 4Mb CF memory card. I should be able to leave the camera sealed in its housing all day or maybe longer on a dive trip.

The Hugyfot housing exudes good quality in the way it is manufactured from aluminium. Open it up and youll see a lot of electrical components that enable it to be set up with different makes of flashgun in TTL mode.
It is slightly tedious to open, because a hexagonal wrench is needed. It wont get unlatched accidentally in the freshwater rinse tank, but you will need to search for the right tool each time.
The camera slips onto its mounting-plate to be held in place by a conventional tripod screw and a second screw-in locating pin.
You have to ensure that the camera and housing switches are in the On position, and that some other rotating switches are corresponding, camera to housing.
You then connect the flash lead to the hot shoe, being careful not to damage the two little LEDs of the Hugycheck system. With the battery previously installed under the camera mounting-plate, these will be flashing red.
The back of the housing is then dropped onto the front half of the clamshell case so that the two hexagonal-ended bolts locate.
The O-ring that makes the seal looks skinny but the Hugycheck leak-testing system provides peace of mind.
I did notice that it was possible to tighten up the two bolts further once it was under water, but you would need to have that hexagonal wrench with you.

You then check that all the controls function properly, the cameras design dictating the position of the camera controls.
The Hugyfot housing uses very nice-looking buttons, but I have a couple of reservations. With many functions, you need to press in a particular button and, at the same time, rotate the command dial, which translates into a rotating knob at the back of the housing. However, as with many other housings, this is very difficult to do while holding it under water.
Another camera housing I have allows you to lock in the main button, then use the same hand to rotate the command knob while you take the weight of your rig, complete with flashguns, in the other hand.
Not so this Hugyfot. The designer has made the housing very anatomically, but then added the necessary handles. I think they need to be about a centimetre closer to the housing to allow easy use of the controls.
The wheel for the lens-aperture control ticks out some distance away from the housing on a long stalk. Its as if the designer was uncompromisingly pursuing a nicely rounded housing, with this as an afterthought.
On the other hand, the shutter-release has been designed to merge with the line of the housing to such an extent that I often missed a shot while fumbling around for it after adjusting the aperture wheel. This might be less of a problem without the right-side handle.
The camera and housing did feel a little negatively buoyant in the water, and that was enough to make my arms feel tired once I started to get cold.

Having two bulkhead connections for the flash is very useful, though I tended to link my second flashgun by photocell slave, rather than have an extra wire.
I was hoisted on my own petard when one of my flashguns decided to cease working from its cell. The problem was solved before the next dive, by making the other the slave and swapping the cable around.
I liked the way my flash-arms mounted directly to any of three ball-mounting points, including one on the optional extra handle.
I used the 16mm Nikon fish-eye and a 20mm Nikon rectilinear wide-angle lens behind the Hugyfot acrylic fish-eye dome port.
Ports are mounted using a bayonet system, but there was no tendency for the big dome to rotate undone by accident.
I cant say it was a good test of sharpness, because I was working in quite poor conditions of visibility, in very cold water in which thermoclines caused some refraction.
When its time to retrieve the camera, the Hugycheck valve is unscrewed, accompanied by a satisfying inrush of air. The LED lights up red.

A POSTSCRIPT TO MY HUGYFOT EXPERIENCE occurred at Zagreb airport, where the security people, unperturbed by cameras and diving equipment, spotted the Hugycheck pump and its 9V battery by X-ray in my luggage.
Vot eez zees they asked.
Be careful how you say the word pump to airport security people. It can so easily sound like a B-word!
Whatever my criticisms of the Hugyfot housing, I wouldnt risk such an expensive camera and lens in one that didnt have a non-destructive leak test system - so Ill have to learn how to use it.

PRICE FX Nikon D700 with 16mm Fish-eye lens, around £2500; Hugyfot housing with fish-eye dome port and Hugycheck system for around 3000 euros
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%