Light is all that we capture as photographers. The more we understand how it behaves the more control we have over out images. Underwater light acts differently and is affected by: 1/ Distance from subject 2/ Floating materials in the water – plankton, sand and so on. 3/ Depth 4/ Weather 5/ Time of day 6/ Surface conditions
Additionally water is 800 times denser than air. So what!? Well this increased density means water absorbs light, decreases contrast and sharpness resulting in dull monotone images. So being close your subject and/or having ideal conditions with minimum particles in the water is essential for clarity in images. There are many times when this is not the case and to get the best images you will have to repeatedly go back until the conditions and light are correct – much the same as other forms of nature photography.
Depth has the effect of filtering colour out of the water and past 5 meters red has already totally disappeared with all other colours other than blue rapidly disappearing by 30 meters. You can see this in the image above! Some of this light can be restored using strobes. The direct effect of water filtering light is, that no matter how powerful your strobes are, if you are more than 2.5 meters away from your subject (5 meters travelled for light to go from strobe to subject to sensor) you will not have red in your photo – no matter how big or expensive your strobe are!
The weather affects the amount of ambient light available with clouds additionally filtering out much of the light, this is exasperated in underwater photography compared to land based photography as the water surface reflects light too. The amount of surface light reflected is directly related to the angle of the sun and wave condition. The lower the angle and the smoother the sea (less waves!) the more light is reflected and does not make it into the water.
Now I come to how I set up my camera, it is not the only way, but hopefully this will give you some tips and get you thinking about your camera setup. To capture the photos I use only RAW. As mentioned the underwater world is not an easy environment for photography and cameras have not really been designed to work in this environment, so the ability to fine tune the images in post-process is critical and JPEGs just don’t cut it when it comes to the required post-processing!
For the setup of my camera with strobes I favour full manual control over ISO, shutter and aperture settings with autofocus on and in servo mode. I do not have TTL connectors (through the lens light metering) for my housing so the strobes are set to manual as well. In fact I am not sure how effective TTL is underwater anyway.
If I am not using strobes I use aperture priority (Av) mode and an ISO of 800+ trying to achieve as high a shutter speed as possible for a sharp image. (Note: It is nearly always necessary to underexpose by a full stop or two with the fisheye).
For focus setup I use single spot focus on the centre point as that is the most sensitive focus point and with the low light environment the autofocus can be fooled at times and end up hunting. You can get around this issue for close subjects, with a focus light – conveniently built into my strobes. This is much better than a torch as it automatically turns off before the strobes fire and back on again after.
A tip for focus lights use - if you use a red filter you are much less likely to disturb the animal before the strobes fire as most fish do not see red. A white light exposes them to predators and so they tend to move off.
For 10 years I used only natural light for my underwater photographs but recently have started using strobes which works especially well for macro. However the addition of strobes has also added complexity. It seems you do not get anything for free!
Strobes and Sync Speed
Once you move onto using artificial light there are some issues you may not have thought about. Yes here we are talking about sync speed! My initial use of strobes brought the subject of sync speed to the forefront of my attention. After getting out of a dive and finding black bands through all my photos I thought my camera had malfunctioned but alas no – sync speed! What does this mean? Well essentially with my Canon 5D mark II, I can only use a maximum shutter speed of 1/200th because any faster results in banding. All SLR cameras suffer from this limitation but not all cameras have the same sync speed - this is where Nikon SLRs do have a better offering with a sync speed of 1/320th. Some micro four thirds cameras also have higher sync speeds.
I have not found it to be a massive hindrance and for macro it is rarely an issue as when using such small apertures of f/16 and below there is little ambient light to worry about. For landscape and portraits however the limited shutter speed can cause motion blur to the background. Although I use Canon exclusively I would consider changing to Nikon next time I upgrade - which is a shame as I own much Canon glass and other bodies. Finally there is one other alternative to combat sync speed - but there is a cost and I cannot afford to get a medium format camera, lenses and housing; and that would also be MASSIVE underwater!!!
I find strobe positioning to be subjective and I am forever moving mine around underwater and adjusting the power output as required. However the objective is not just to light the subject and control shadows but also to minimise backscatter caused by particles in the water. Having the strobes angled to the subject and back slightly from the front of the lens while not directly parallel will help a lot. To further minimise scatter shooting across the direction of natural light helps too. Ultimately, the strobes bring out the wonderful colours of the underwater world, as you can see in the image of the clown fish above.
In the next and final section I will cover lenses, capturing the image and post processing.