hspace=5 WHY ON EARTH WOULD ANYONE SPEND the thousands of pounds needed to buy a digital SLR camera (DSLR) and housing, when high-quality digital compact cameras with their housings can be bought for one tenth of the cost, offer the advantage of a variable-angle lens with the ability to switch from macro to wide-angle under water, and are so convenient to carry
The answer is that compacts take time to switch from writing to the LCD used as a viewfinder to writing to the card, and once they have grabbed the shot, if you want a big RAW file (if its possible), it takes time to write that too.
All of which means you might miss the next shot. Those compacts with a high megapixel rating often suffer from digital noise at high ISO settings, too.
The viewfinder of a DSLR gives you an optical image exactly as seen by the lens via a mirror. This swings out of the way when you take the picture, and swings back afterwards.
The effect is almost instantaneous, although purists would argue that the viewfinder is blanked out at the exact moment the picture is made.
DSLRs also employ a buffer. This means that they allow you to take more pictures while the previous one is being recorded to the memory card. This is very important if you shoot RAW files (more of that later), and it makes picture-taking seamless.
You can spend between 400 and 5000 on a similar-looking DSLR, so what are the differences and which suits an underwater photographer best
When you add the cost of a suitable lens (prices shown here are for bodies only) and an underwater housing with lens port, it is always going to add up to a lot of money.
Also, never forget that you are taking your camera into a hazardous environment that can destroy it in a moment.
Cost apart, what are the disadvantages of a DSLR You cant change lenses under water, so you have
to decide if you are going to shoot wide-angle or macro before you jump in. There is also the added size and weight.

Sensors
DSLR cameras come with a variety of sensor sizes, but they are invariably bigger than those of any compact camera. Whats the advantage of a bigger sensor You get less digital noise (grain) for a given megapixel rating and light-sensitivity setting (ISO).
Bigger sensors give better results in low light conditions. There are electronic imperfections in
the necessarily smaller-sized individual light-sensitive pick-ups of smaller sensors, and smaller electronic pick-ups also suffer more chromatic aberration, causing a lack of sharpness.
Sensors are usually either full-frame or FX - the same size as a conventional frame of 35mm film (about 36 x 24mm), or smaller at around 24 x 16mm. They are sometimes referred to as APS size, after that old film format. Sometimes they are called cropped sensor or DX cameras.
Some manufacturers such as Olympus have introduced sensors that are less than full-frame but have a squarer shape. Instead of being 3:2 they are 4:3, but they are invariably smaller than APS.
There is a saying in the world of boxing that a good bigun will always beat a good littlun. Among camera-users on land, the saying also holds true. But is it the case under water Read on...

Lenses
A smaller sensor allows the camera to be used with a shorter focal-length lens for the same angle of view. This gives a better depth of focus for a given lens opening (f/number) - an advantage when it comes to taking macro shots through a flat port of an underwater housing.
However, if you want to shoot wide-angle pictures, youll need an optical dome port. This, as its name implies, becomes part of the optical system. The image focused on by the camera lens is actually a virtual image formed a short distance in front of the port, due to refraction where air and water meet.
One of the bigger challenges of taking wide-angle pictures through a curved dome port is in achieving a sharp image across the frame. Wide-angle lenses that have been designed to have a flat field of view, as one would need when using them in air, tend to be less able to focus on this curved virtual image across its width, and chromatic aberration (colour-fringing) is then evident.
Ironically, adding a strong dioptre supplementary close-up lens often adds the lens aberration and distortion needed to get it sharper, but a lot of wide-angle underwater pictures still have horribly smudged details at the extremities.
The bigger the sensor, the longer the focal length of the lens needed and the bigger the dome port required for a sharply focused picture of the virtual image so produced in water. Supplementary dioptre lenses also shorten the focal length of a given lens, allowing it to focus closer for a given lens-to-sensor distance.
So a bigger sensor means using a bigger dome port for the same quality of picture. A full-frame camera may need a housing with a 9in diameter dome port, whereas the cropped sensor DSLR will need only a 6in dome.
This is probably why medium-format cameras never became popular under water - they would need even bigger domes. It was just too difficult to get a satisfactorily sharp picture. So theres an optimum size of sensor, depending on the angle of view of the lens being used.
On the other hand, if you are shooting in low light conditions where the high ISO settings needed would produce too much digital noise on a cropped sensor, it might be worth trading off edge sharpness against the reduced grain of a bigger full-frame sensor.

Camera Bodies
Nikon makes a range of cameras that use a cropped sensor, and flagship professional models the D700 and D3, which are full-frame. Canons track record is based more on full-frame cameras, but it also offers cameras with cropped sensors.
As a broad judgment, full-frame cameras offer the ultimate quality in air, and with flat macro ports on underwater housings, whereas cropped-sensor cameras make it easier to get pictures sharp from edge to edge with wide-angle lenses behind dome ports. The latter also give the user the option to use less powerful ancillary flashguns, because they have the same depth of focus at the wider lens openings required.
Recently, underwater photographers have discovered that the inherent design faults of some lenses that decrease their usefulness on land actually enhance their performance under water, behind a dome port.
The popular Tokina 10-17mm Fish Eye lens is a case in point. It suffers from horrible barrel distortion and poor edge sharpness when used in air, but behind a dome port this is negated. Many of the pictures you now see routinely reproduced in these pages are made with such a lens and, being of variable focal length, it is good for both wide-angle and certain close-up shots.
People who have owned 35mm film SLR cameras before going digital often choose an equivalent brand to use the lenses they may already have. This doesnt always work well, unless the digital sensor is full-frame, like the film camera.
The 20mm very-wide-angle lens will be equivalent to a 30mm not-so-wide-angle lens on a camera with a cropped APS-size sensor. Longer lenses become effectively longer, which can help with macro shots, but remember that with a bigger image-circle than is needed forming inside the camera, due to internal flare you might get reduced contrast results when photographing something dark surrounded by brightly lit surroundings.
Cheaper versions of some DSLR cameras have no focus servo in the body, and rely on a servo-motor in the lens. You might buy an economical camera only to find that you are denied the use of economically priced lenses from independent manufacturers and need to buy expensive proprietary lenses with built-in auto-focus drives.

Housings
An underwater housing is basically a box that keeps the water at bay yet lets you have full use of the camera controls. Underwater photographers have their brand allegiances, but the design of each housing is always limited by the position of the operating buttons on a specific camera.
Submarine housing manufacture is a cottage industry. Very limited numbers of finished units are produced, because Japanese camera manufacturers regularly bring out new models that make previous models obsolete.
Most of the high-quality machined metal housings are made for the two brands of DSLR camera that have proved most popular with underwater photographers - Nikon and Canon.
The Fuji S5 Pro is actually a Nikon body with a Fuji sensor and electronics.
Olympus and Sony (Minolta) also both make a DSLR camera, but the choice of housing and therefore the availability is very limited.
US company Ikelite makes submarine housings from Plexiglas, and though these are less sophisticated than an aluminium housing, they can fit almost any DSLR specified at the time of purchase. Its just a matter of drilling the holes
for control rods in the right places, so if you already own one of these cameras, this is probably the way to go.
Fantasea Line is another manufacturer of plastic housings for DSLR cameras. Olympus makes a plastic housing for its own camera. Remember, once you own a housing, it will only fit the camera for which it was intended. Big cameras demand bigger housings. A housing for an obsolete camera can become an expensive white elephant.

Pixel Ratings
The pixel-rating was important in the days when the 1 megapixel barrier was first broken, and it has been a marketing tool ever since. Today pixel-ratings can vary from 6 to 12 megapixels, even with inexpensive compact cameras.
I regularly use a 6 megapixel DSLR, because pixel-rating is just a measure of the size to which a picture can be enlarged, rather than of its overall quality, which depends on sensor size and design.
The camera I use for studio shots has an APS-size sensor with dual pick-ups for both highlights and shadows. This gives a better dynamic range but poorer sharpness than a DSLR with the same pixel-rating, but its still sharper and with less digital noise than almost any digital compact, even those with higher pixel-ratings.
If your pictures are for personal use, youll gain little advantage in having a camera of more than 6-megapixel capability. If you want to supply
high-quality images for reproduction at 300 dots per inch in magazines, a 10 megapixel DSLR may give you an advantage, while a 12-megapixel-rated DSLR will enable an art director to crop into your shot, yet still use it as a double-page-spread.
Cameras with much higher pixel-ratings are really intended for pro photographers whose images may end up on 64-sheet street hoardings, and would represent a huge financial risk if taken under water.

CCD or CMOS
Two different sensor designs are commonly employed in DSLR cameras: CMOS (complimentary metal oxide semiconductor) or CCD (charge coupled device). Both can offer excellent imaging performance.
One could argue that CMOS offers higher light sensitivity, while CCD gives better dynamic range. Both use a Bayer array or system of RGGB filters over the cells. Because there are twice as many green pick-ups, digital noise when it occurs is usually most obvious from the red and blue pick-ups.
This filter array also means that there may be problems at the edges of any sensor where the light from the lens strikes at an acute angle, another problem that is more acute for larger sensors and wide-angle lenses. Sensor development might take a different direction altogether in the future.

Sensor Cleaning
When cameras have interchangeable lenses, especially those used in harsh outdoor conditions, dust or foreign bodies will be attracted to the sensor. This shows up as unattractive blobs in pictures. Some say that because of an inherent electrostatic charge, larger CMOS sensors suffer more from this than smaller CCD sensors.
The best-equipped cameras now come with built-in sensor-cleaning, either by vibration or a blast of air. This removes the nerve-wracking process of using special swabs and cleaning fluid.

Image Files and Processing
Bigger files require more storage space, both in the camera in the form of its media card and, more importantly, afterwards, when you need to both store and back-up your growing collection of images. This can add significantly to the cost of your photography.
The quality of the image produced doesnt stop at the camera. You can shoot jpegs with all these DSLR cameras, but if its high-quality imagery youre after, youre missing the point unless you use the RAW file option. Jpegs are compressed files processed automatically within the camera using onboard software - great for holiday snaps as there is no further work to do, but youre missing out on what your sophisticated camera can do.
Professionals and serious underwater photographers record RAW files, which record all the information picked up by the cameras sensor so that you can rearrange it as you want it later on your Mac or PC with no loss of quality.
This is especially useful for the underwater photographer who may be limited by time for decision-making at the moment of shooting. Exposure, contrast, white-balance, sharpness and even vignetting can be decided on later.
You can save highlights that are too light, or shadows that have lost detail. You can even add fill-in lighting effects. It in no way degrades the quality of the original image, and it saves getting it wrong in haste while under water.
You need suitable software with a compatible RAW converter. Some of these are very basic, but
if you get a full-function version as supplied with Photoshop CS3 or Aperture, the sky is the limit in terms of creative control and image quality.
This is why comparing images processed within the camera using its own mini-computer and software can be misleading.

So which camera
Each model has its advantages and trade-offs. We have pulled out typical comparative specs for 23 commonly used cameras for comparison.
Some of these models may be unavailable as new by the time you read this.
Whichever camera you choose, its important to come to terms with the fact that a newer improved model that replaces it will almost certainly hit the shops before you have digested the instruction manual, so take pictures with what you have and enjoy it!


width=100% width=100%NIKON £330
D60

An economical way to get high-quality Nikon results akin to those previously obtained with the highly thought of D200, but be aware that because it has no built-in focus drive for lenses, you may need to pay more for lenses that have their own servo motors. It uses a cropped sensor and works best with Nikons DX lenses.

BODY: Plastic
SENSOR: Cropped DX CCD
METERING: 3D matrix
MEGAPIXELS: 10
MONITOR: 2.5in LCD
SENSOR CLEANING: Airflow
AUTOFOCUS: 3-area
(No built-in focus drive)
ISO RANGE: 100-1600
STORAGE MEDIA: SD/SDHC

width=100% width=100%CANON £450
EOS-450D Rebel Xsi

A popular choice among those who buy Canon DSLRs around the world and take them under water, thanks to its economically built mixed plastic and metal body and 12-megapixel cropped CMOS sensor. Unlike many of the other DSLRs featured here, it records to an SDHC memory card.

BODY: Plastic with stainless-steel chassis
SENSOR: Cropped CMOS
METERING: 35-zone
MEGAPIXELS: 12.2
MONITOR: 3in LCD
SENSOR CLEANING: Low-pass vibration
AUTOFOCUS: 9-point
ISO RANGE: 100-1600
STORAGE MEDIA: SD/SDHC

width=100% width=100%CANON £630
EOS-40D

Probably the most popular choice of DSLR for underwater use among Canon fans, this is a cropped CMOS 10-megapixel sensor camera with a tough metal body.

BODY: Magnesium alloy
SENSOR: Cropped CMOS
METERING: 35-zone
MEGAPIXELS: 10.1
MONITOR: 3in LCD
SENSOR CLEANING: Integrated system
AUTOFOCUS: 9-point
ISO RANGE: 100-1600
STORAGE MEDIA: CF

width=100% width=100%NIKON £670
D90

Although the D90s body is less robust than that of its more expensive siblings, this may not matter if its always protected inside a submarine housing. When it comes to underwater use, expect the same sort of picture quality as with
the more expensive D300. It also shoots video! Manufacturers are rushing to get suitable housings into production.

BODY: Aluminium & Plastic
SENSOR: Cropped DX CMOS
METERING: 3D matrix
MEGAPIXELS: 12.3
MONITOR: 3in LCD
SENSOR CLEANING: Self-cleaning sensor
AUTOFOCUS: 11-area
ISO RANGE: 200-3200
STORAGE MEDIA: SD/SDHC

width=100% width=100%NIKON £920
D300

Probably the most popular solution at this time for those that want to take a DSLR under water, it squeezes a lot of megapixels onto a cropped sensor, but at the same time promises better depth of field for optically sharper pictures, and good wide-angle results from DX lenses. Manufacturers tell us they now make more underwater housings for this DSLR than any other.

BODY: Magnesium alloy
SENSOR: Cropped DX CMOS
METERING: 3D matrix metering
MEGAPIXELS: 12.3
MONITOR: 3in LCD
SENSOR CLEANING: Self-cleaning sensor with low-pass vibration
AUTOFOCUS: 15 cross-sensor with 51 or 11 focus points
ISO RANGE: 200-3200
STORAGE MEDIA: CF

width=100% width=100%CANON £1200
EOS-50D

Said to be a model that complements the EOS-40D rather than replacing it, its 15-megapixel sensor and promise of reduced noise ratios makes it capable of top-quality results. It has a new high-resolution LCD too.

BODY: Magnesium alloy
SENSOR: Cropped CMOS
METERING: 35-zone
MEGAPIXELS: 15.1
MONITOR: 3in LCD
SENSOR CLEANING: Integrated system
AUTOFOCUS: 9-point
ISO RANGE: 100-1600
STORAGE MEDIA: CF

width=100% width=100%NIKON £1690
D700

A more compact version of Nikons full-frame formula means that a submarine housing will not need to be so large, and yet it promises image quality as good as the best. We imagine that top underwater photographers who use full-frame sensor Nikons will go for this one.

BODY: Magnesium alloy
SENSOR: Full-frame FX CMOS
METERING: 3D matrix
MEGAPIXELS: 12.1
MONITOR: 3in LCD
SENSOR CLEANING: Self-cleaning sensor with low-pass vibration
AUTOFOCUS: 15 cross-sensor with 11/51 focus points
ISO RANGE: 200-6400
STORAGE MEDIA: CF

width=100% width=100%NIKON £3000
D3

This is Nikons flagship professional camera, with a body that will take a lot of hard use and electronics that will give the best-quality imagery. At the price, we cant imagine too many people will risk taking one under water, but we can dream!

BODY: Magnesium alloy
SENSOR: Full-frame FX CMOS
METERING: 3D matrix
MEGAPIXELS: 12.1
MONITOR: 3in LCD
SENSOR CLEANING: Sophisticated self-cleaning by vibration
AUTOFOCUS: 15 cross-sensor with 9/12/51points, and 3D tracking
ISO RANGE: 200-6400
STORAGE MEDIA: Dual CF

width=100% width=100%CANON £4400
EOS-1 Ds Mk3

With a 21-megapixel full-frame sensor, Canon ups the ante on practical image sizes possible. Its a manufacturers answer to retaining the top spot in camera specifications. This is Canons flagship professional camera, and Canon aficionados will dream of taking one under water, even if few actually dare to do so!

BODY: Magnesium alloy
SENSOR: Full-frame CMOS
METERING: 63 zones
MEGAPIXELS: 21.1
MONITOR: 3in LCD
SENSOR CLEANING: Integrated system
AUTOFOCUS: 45-point
ISO RANGE: 100-1600
STORAGE MEDIA: CF and SD

NIKON D40 £260
BODY: Plastic
SENSOR: Cropped DX CCD
METERING: 3D matrix
MEGAPIXELS: 6
MONITOR: 2.5in LCD
SENSOR CLEANING: Manual
AUTOFOCUS: 3-area (No built-in focus drive)
ISO RANGE: 200-1600
STORAGE MEDIA: SD/SDHC
OLYMPUS E-420 £300
BODY: Plastic
SENSOR: 4/3 CMOS
METERING: 49-zone
MEGAPIXELS: 10
MONITOR: 2.7in
Sensor Cleaning: Supersonic wave filter
Autofocus: 3-point auto
ISO RANGE: 100-1600
STORAGE MEDIA: CF and xD

SONY Alpha-200 £300
BODY: Plastic
SENSOR: Cropped DX CCD
METERING: 40-segment
MEGAPIXELS: 10.2
MONITOR: 2.7in LCD
SENSOR CLEANING: Dust reduction system
AUTOFOCUS: 9-point
ISO RANGE: 100-1600
STORAGE MEDIA: CF and Memory Stick Duo
NIKON D40x £350
BODY: Plastic
SENSOR: Cropped DX CCD
METERING: 3D matrix
MEGAPIXELS: 10.2
MONITOR: 2.5in LCD
SENSOR CLEANING: Manual
AUTOFOCUS: 3-area (No built-in focus drive)
ISO RANGE: 100-1600
STORAGE MEDIA: SD/SDHC

CANON EOS-1000D £400
BODY: Plastic with stainless-steel chassis
SENSOR: Cropped CMOS
METERING: 35-zone
MEGAPIXELS: 10.1
MONITOR: 2.5in LCD
SENSOR CLEANING: Low-pass vibration
AUTOFOCUS: 7-point
ISO RANGE: 100-1600
STORAGE MEDIA: SD/SDHC
FUJI S5 Pro £500
BODY: Magnesium alloy (as D200)
SENSOR: Cropped DX Super CCD SR
METERING: 3D matrix
MEGAPIXELS: 12.2
MONITOR: 2.5in LCD
SENSOR CLEANING: Manual
AUTOFOCUS: 11-area
ISO RANGE: 100-3200
STORAGE MEDIA: CF

NIKON D80 £500
BODY: Plastic
SENSOR: Cropped DX CCD
METERING: 3D matrix
MEGAPIXELS: 10.2
MONITOR: 2.5in LCD
SENSOR CLEANING: Manual
AUTOFOCUS: 11-area
ISO RANGE: 100-1600
STORAGE MEDIA: SD/SDHC
OLYMPUS E-520 £550
BODY: Plastic
SENSOR: 4/3 CMOS
METERING: 49-zone
MEGAPIXELS: 10
MONITOR: 2.7in LCD
SENSOR CLEANING: Supersonic wave filter
AUTOFOCUS: 3-point auto
ISO RANGE: 100-1600
STORAGE MEDIA: CF and xD

Nikon D200 £675
BODY: Magnesium alloy
SENSOR: Cropped DX CCD
METERING: 3D matrix
MEGAPIXELS: 10.2
MONITOR: 2.5in LCD
SENSOR CLEANING: Manual
AUTOFOCUS: 11area
ISO RANGE: 100-1600
STORAGE MEDIA: CF
SONY Alpha A-700 £750
BODY: Magnesium alloy
SENSOR: Cropped DX CCD
METERING: 40-segment
MEGAPIXELS: 12.25
MONITOR: 3in LCD
SENSOR CLEANING: Dust-reduction system
AUTOFOCUS: 11-point
ISO RANGE: 100-1600
STORAGE MEDIA: CF and Memory Stick Duo

OLYMPUS E-330 £1100
BODY: Magnesium alloy
SENSOR: 4/3 CMOS
METERING: 49-zone
MEGAPIXELS: 10.1
MONITOR: 2.5in LCD
SENSOR CLEANING: Supersonic wave filter
AUTOFOCUS: 11-point
ISO RANGE: 100-3200
STORAGE MEDIA: CF and xD
SONY Alpha-900 £2325
BODY: Magnesium alloy
SENSOR: Full-frame CMOS
METERING: 40-segment
MEGAPIXELS: 24.6
MONITOR: 3in LCD
SENSOR CLEANING: Dust-reduction system
AUTOFOCUS: 9-point
ISO RANGE: 100-3200
STORAGE MEDIA: CF and Memory Stick Duo/PRO Duo/PRO-HG Duo

CANON EOS 5D MK2 £3000
BODY: Magnesium alloy
SENSOR: Full-frame CMOS
METERING: 35 zone
MEGAPIXELS: 21.1
MONITOR: 3in
SENSOR CLEANING: Integrated system
AUTOFOCUS: 9-point
ISO RANGE: 100- 6400
STORAGE MEDIA: CF type 1 & 2