(This article was first published in Dive New Zealand April/May 1998)
Tips and tricks for underwater video.
There are probably as many reasons for people going diving, as there are divers out there. Most of us would agree, though, that the amazing world of underwater life and seascapes sets diving aside from just about any other activity we can think of. Where else can you float weightless around for about an hour watching creatures in all the colours of the rainbow getting on with their lives?
There is a lot for the eye to enjoy, and I have always found that one of the particularly interesting features is the way in which nature is using colours under water - and I think I am not alone in this observation.
No wonder, then that coral gardens, kelp forests, tropical and NZ fishes, colourful algae, sea urchins, and many more features of the underwater world are the target for diving photographers around the world.
For the video enthusiast, however, it is a real challenge to capture these colours and reproduce them back on the TV screen.
Anyone who has done underwater video has had the disappointing experience of coming home from a great dive with lots of colours only to find that all the shots on video have turned out blue or green - none of the real colours down there seem to have made it on to the video tape.
Frustrating, yes, but there is an explanation and some options on what to do.
The deep blue - it's really true.
In principle the sun's rays contain all the colours of the rainbow mixed together, and
this makes for a kind of white light which will let any colour stand out - when we are not
diving, that is.
Under water things are different.
The water mass works just like any other filter we put between the source of light and what we are looking at and at the same time like a filter between our eyes and the object of interest.
In a television studio we can change the colour of light with a variety of coloured plastic sheets, gels. Yellow gel in front of the lights gives us a warm yellow colour tone on the set. Similarly a blue gel will cool the set in a bluish hue.
And if you put on a pair of blue sunglasses, yes, let us state the obvious, everything looks blue.
Under water the sunlight, whether direct or diffused by clouds, penetrates the water surface and hits a fish, a rock, a piece of coral or another diver. The fact that we can see anything down there at all is because the sun is lighting everything we are looking at.
The deeper you go the fewer colours. The analogy is putting more and more blue gel in front of a light in the television studio, or wearing a couple of extra blue coloured sunglasses on a bright day.
The deeper we go, the thicker the layer of water the sun's rays must penetrate, the more colour is lost.
Video cameras have a particularly nasty way of reacting to the change of light. They seem to record things in completely blue or green hues. Everything gets almost monochrome and more bluish than it really is.
Colour filters
A way of getting around this problem (to some degree, at least) is to compensate for the
loss of colours by inserting a filter in front of the lens. Often this is called a
"red-filter" because of its colour. Depending on conditions this filter will put
some colour back into the shot. Back to the analogy: You are wearing blue sunglasses,
everything looks blue. Now put a pair of orange or red glasses in front of the blue ones,
and, surprise, some of the colours come back.
 | The red filter is a help, but must be used with caution: Near the surface, (how near depends on conditions), the filter overcompensates and your footage will look yellowish or too red. Because you are shallow, the water mass between your object of interest and the sun's rays on the surface is not great, and therefore there is more colours left in the light. |
| The further away your object is, the less effect the filter will have - and vice versa. Imagine a bright red object right in front of you. As you get further away from this object, the red will slowly disappear and become washed out in blue or grey. The reason is that you now have a great mass of water between you and the red object, filtering the colour out. A black and white picture would not suddenly turn to full colour just because you put your sunglasses on, and similarly, a filter would not put red back into the shot, once it is gone. |
| When shooting close-up shots and using lights, the filter can either over-saturate the colours or outright distort them. When you use lights you are actually replacing sunlight with artificial light. If your lights are strong enough and you are close enough, the white rays in your lights will enable you to see the colours clearly. If you then put a red filter in front of the camera it works just like wearing those sunglasses, the colours get distorted. Therefore, as a rule of thumb, always remove the filter when using lights for close-ups. |
| If you have a monochrome (black and white) viewfinder, remember that the picture looks exactly the same with or without the filter on. It is really important that you remember when to use it and remove it. Make it a routine always to check if the filter is ON or OFF for every shot you take. There is nothing worse than coming home to watch those pictures to find that half of them are red and the other half are blue. |
| If you use a Digital Video camera which can manually white-balance like the Sony VX1000 or Panasonic's EZ1, then try to do a white balance on a white slate without the filter on. This is sometimes sufficient to get the colours out. |
| External filters (those you fit on the outside of the dome port or wide angle lens) can pick up small air bubbles when you are not using them. The tiny bubbles stick to the surface of the filter. A couple of waves with a hand will flow them off. It is really important to check this, as you are likely to see the bubbles as small spots on your screen afterwards. Another problem you can get is that your focus mechanism will focus on the bubbles and not on what you really want to look at. |
| Internal filters (those that flick down in front of the camera lens inside the housing) can sometimes "fall" down if you bump the housing against something, and you end up using the filter where you did not mean to do it. You have to check that this does not happen, best with a colour viewfinder. |
| The colour temperature of the ocean is not the same everywhere. Tropical water is typically very blue. NZ waters range from blue to more green. The Atlantic is even greener. Housing manufacturers have filters, which match different locations. The red or orange filter is the most common used by NZ divers. |
Filter use: variable dive conditions
How deep are you? Generally, the filter must be applied from around 8 metres depth, but also keep the following in mind:
Is it a cloudy day or bright sunshine up top? This affects how deep the sun's rays penetrate and therefore the depth at which the filter becomes necessary.
At what angle is the sun during the dive? If the sun is low, it's rays must travel through more water to reach your object of interest, and the filter has to be applied at a shallower depth than if you were diving at midday with the sun right on top of you.
Are you in tropical or tempered waters? Tropical waters, being bluer, tend to call more for the use of filter than tempered waters. You will generally need to apply the filter at a shallower depth in tropical waters than in tempered waters like here in NZ.
Are you shooting a combined close-up foreground with a distant background? If so, you have to choose whether to get a bluish background or risk an oversaturated close-up.
As always experience is the best way to find out what works best for you, but hopefully the above is a help to get started.