Lesson 4 The Underwater Photo Course
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Camera Features

Composition Systems

The viewfinders on almost all the cameras provide a window through which you can see an approximation of the picture the camera will take, along with some status information about perhaps shutter speed and strobe function.

Non-reflex viewfinders

The more common systems all have non-reflex viewfinders, which is a small window in the camera body, set to give a view that matches that of the standard lens for that camera. In this category we can include:

One particular, and serious problem associated with the use of any non-reflex viewfinder is that of parallax error. This occurs when photographing close subjects, and is because the viewfinder, which is located above the centre of the lens by up to a few inches, sees a different picture than the lens does.

fig11.jpg (10576 bytes)

Figure 11. Parallax error.

Some viewfinders contain parallax correction marks, but these are usually set for about the 3 foot mark, and you will frequently want to take photographs closer than that. There are a number of manual techniques that can be employed, such as tilting or moving the camera just before you press the shutter, but in my opinion this makes composition rather a hit or miss affair.

In any event, the standard viewfinder is only good for the standard lens, and when using wide-angle lenses you will have to purchase an accessory viewfinder to match the lens. These viewfinders range widely in price, and are frequently useful with only the lens they were designed for.

One of the models offered by Sea & Sea has adjustable masks for use with a variety of lenses, and also a calibrated tilting mechanism to compensate for parallax errors, and is certainly worthy of investigation as it is useable with both the Sea & Sea and Nikonos cameras.

Accessory viewfinders provide a remarkably large and clear image, and can easily be used from distances of over a foot away, saving you from having one eye glued to the viewfinder all the time. Even those who have housed cameras may wish to consider the use of accessory viewfinders in fixed focus wide-angle action photography.

Reflex viewfinders

The principle of reflex viewfinders is that light coming through the lens is reflected off a mirror and directed through to the viewfinder. This is the way in which normal Single Lens Reflex cameras work.

Cameras with this system will naturally include any housed SLR, and also the Nikonos RS, which is effectively an SLR in a fully waterproof body, rather than a housing.

Composition will always be spot on with such systems, as you are seeing exactly what the lens is seeing. The only thing to be careful of is that many viewfinders do not show all of the picture that eventually ends up on the film, with cameras such as the Nikon F90 only showing 92% of the final image through the camera (let alone the housing) viewfinder.

The down-side of these housed systems is that the most cameras were originally designed for use with the eye close up to the camera. The intervention of a housing and a diving mask between them can mean sometimes that the whole viewfinder cannot be seen. This effect is lessened when using a low-volume diving mask, and by housing cameras that have larger brighter viewfinders, variously called Action-finders, Sports-finders, or High-eyepoint viewfinders.

Nevertheless some housing manufacturers have recognised this problem, and market supplementary lenses that can be attached or installed to the back of the viewfinder port on the housing. These in effect reduce the size and brightness of the viewfinder image, but permit it to be viewed in whole from much further away. Some also contain a diopter adjustment, so that you can match it to your eyesight, but none are cheap, matching the price of the more expensive accessory viewfinders.

Exposure Systems

An essential component of the exposure system is the sensitivity of the film itself. Some cameras require you to manually set the film speed when you load your camera with film, while others have special electrical contacts which read the DX codes on the film cassettes and set the speed automatically. It is therefore very important with these cameras to keep these electrical contacts clean, and never to cover up the bar-code on the cassette with sticky labels before the film is exposed.

Available light

Most systems with a built-in light meter will tell you when it considers there is the right amount available light to take a photograph, leaving you to adjust the shutter speed and aperture as you will.

The Nikonos IV and Nikonos V models feature an automatic mode where the camera will select the most appropriate shutter speed, but the Nikonos III and earlier had no metering systems, and an accessory underwater light meter, the Sekonic Marine Meter, still in manufacture, was considered an essential item.

The rest of this section is based on my knowledge of housed Nikon cameras, especially the F801s and F90, which have a variety of exposure modes. I have assumed that you are familiar with your camera's controls, and I am not going to explain them in depth. If your housed camera is of another make or model, then read these comments anyway, as they may be relevant to your system also.

Program mode(s)

Aperture Priority

Shutter Priority


Metering modes

In addition to the actual exposure modes, these cameras have a number of options about how the light is metered, reading either from a spot in the centre, from the middle of the frame (centre-weighted), or a balance of the whole frame (matrix). I find that matrix metering works particularly well underwater, and have not yet found a need to use the other modes.

In addition, exposure compensation may be available to permit exposure bracketing of important shots, but be warned that it is easy to set underwater, but equally easy to forget to revert back to the proper setting.

Manual strobe

When using manual strobes with any of these systems, then you must calculate the exposures required, according to the power of the strobe and the distance of the subject, and set these yourself. This will be covered in greater detail in the section on Strobes.

TTL strobe

Generally the camera's TTL system will automatically take a correct strobe exposure for you.

Most systems have a fixed shutter speed (sync speed) which they will set when using a strobe, but housed cameras may permit a variety of speeds to be used. In particular the Nikons will allow the speed to vary from 1/60 to 1/250 in aperture priority mode, and even slower in shutter priority and manual modes. The F90 has an additional feature offering slower speeds while retaining aperture priority, but this feature may not be selectable underwater on all housings.

It is worth noting that a separate metering system is used on the Nikons for TTL than is used for available light, with the F90 offering a wide range of sophisticated modes that is beyond this book to describe, so refer to your camera's operating manual for further details.

Focusing Systems

The less expensive cameras and some entry-level systems may have fixed focus lenses, relying on a small aperture and a consequently large depth of field to render everything into acceptable focus. The main underwater systems have prime lenses with adjustable focus, with recommendations for prime lens focus when supplementary wide-angle lenses are used.

Housed cameras, such as the Nikon F801s and F90, and the Nikonos RS have autofocus systems that can be operated in manual mode, some with indications when correct focus has been reached.

Remember that with reflex systems, focusing will be done at max. aperture, and that depth of field will be greater in the shot than you see through the viewfinder, unless you have access to your depth of field preview button.

Manual Focus

When focusing manually, set your focusing with depth of field in mind, that is, don't automatically focus on infinity, but consider focusing on the hyperfocal distance to maximise the depth of field.


Autofocus is a highly useful tool, but it must be realised that it doesn't necessarily work under all conditions. AF locks onto lines, textures, patterns, contrasts, colours, looking for changes and boundaries, but if it can't find anything, then it will 'hunt', searching from minimum to maximum focus. Circumstances which cause it problems are very uniform subjects, such as the skin of sharks, mantas, and dolphins, and also low light conditions, when you will need to use a spotting torch to provide it with the necessary illumination.

Most lenses allow you to select manual or autofocus modes underwater, but some of the Nikon lenses, particularly the two macro lenses, need a switch moving that is inaccessible with most housings.

If one of these lenses does start to 'hunt', it is possible to override it. Move your finger onto the AF-lock button, lock onto something nearby at approximately the same distance, then physically move the housing backwards and forwards to fine-focus as necessary. Alternatively go onto continuous autofocus mode, and use a light trigger finger, but beware as the camera will quite cheerfully take out of focus pictures for you in this mode.

You won't get autofocus to work for everything, and sometimes have to make a choice before you get in. Some photographers I have talked to use autofocus about 80% of the time for macro work, and manual focus about 80% of the time for wide angle shots.

Always give autofocus a try, but be prepared to switch back to manual where you can.

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This page was last updated on 11 August 1998
Please address any comments to Mark Mumford