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Strobes And Water Colour

This article was published in Underwater Photography Magazine in May 2008 and it has generated plenty of interested so I have reproduced it here. Unlike the other articles on this website you can click on the images to see them in more detail. Note that the third image was not in the original article, but is included here to show the affect of strobe filters.

I expect the title of the article will be causing a bit of head scratching. But please bear with me, this is a relatively new concept but one that is well worth consideration. In this article I want to discuss how the colour temperature of our strobes has the potential to affect the background water colour in our digital photographs.

It certainly sounds confusing to begin with. How can firing a strobe that illuminates the subject and not the water alter the water colour? It requires a different way of thinking about colour in images because of the adjustable white balance of digital cameras. Therefore this is a digital issue and not something that is relevant to slide photography.

I should also say that this is an article about subtle differences. Strobe colour temperature does not make day or night differences to images, it is about that final polish. However, it is often those final finishing touches that make the difference between the good and the excellent. To ignore this issue means giving up an important tool that controls water colour in our images.

I first raised this topic in UWP a couple of years ago, back in Issue 31, but I felt it was worth revisiting in detail. The root of this phenomenon is that the various underwater strobes on sale produce light at different colour temperatures and digital cameras have adjustable white balance that reacts to this.

To keep things simple I am going to lump strobes into warm coloured and cool coloured – using my own strobes as examples. My Subtronic strobes are warm or red biased (my Alphas produce light at 4300 K and the newer Midis at 4800 K), while my Inon strobes are cool blue biased (my Z240 produces light at 5500 K).

When you take a picture illuminated by 5500 K or 4300 K light you will need a white balance close to this value to render neutral colours (see Figure 1, click on first image). This setting is applied to the whole image. In the real world this means that both strobe lit and non-strobe lit areas are affected, and therefore strobe choice can affect the background water colour (see Figure 2, click on second image, above). To prove this to yourself, open up one of your own wide angle images in a RAW converter and try moving the colour temperature slider between 4300 K and 5500 K. Ignore the foreground colour and watch how much the water colour changes.

Another way to explain this concept is to compare the similarities and differences between film and digital. On both media the main factors that will control the background colour we get in our photos are environmental conditions (water colour, depth, climatic conditions etc), camera angle, lens and exposure.

On film we have another important factor to consider. Film choice. Certain films are well known to make big differences in the water colour they record. Even within the Kodak stable photographers used to spend much time debating the differences between the true look of Kodachrome blues compared with the rich royal blues that Ektachrome delivered in the same conditions. Stunning blue backgrounds were known as Ektachrome blue for many years.

When shooting slides strobe colour temperature made no difference to the water colour. If we used a warmer strobe then the only effect would be warmer hues in the foreground lit by a strobe. The background would remain unaffected. This was/is a popular technique, with many photographers favouring warm strobes or warm filtered strobes to improve the skin tones of people in their images.

Digital is different. An approximate analogy to film choice is the cameras adjustable white balance. Shooting underwater, a digital camera will try to make the foreground subject appear neutral, deciding on the appropriate white balance setting for each shot based on the colour temperature of the foreground illumination. When you adjust white balance in the RAW converter you are doing the same thing. Since different strobes require different white balance settings (therefore affecting the colour of the water in your images) – strobe choice on digital is comparable to film choice on slide.

To run through an example, if we use warm strobes then the foreground subject will appear to the camera (or to us white balancing the RAW file in post processing) as too warm and the white balance will be used to cool the image (the Kelvin value will be lowered). Importantly this adjustment is applied to the entire image. Cooling the white balance results in a correct looking foreground and bluer background. If we use cool strobes then the foreground will be too cool and the camera (or us) will attempt to warm it up with the white balance. This will again result in a correct looking foreground and a less blue background. You can see this visually in the real world example in Figure 3 (click on image 2).

It is clear from the examples (Figures 2 & 3) that the effect is subtle, but this difference will there in all your images. The only difference between the two shots in Figure 3 was the type of strobe I used. Once the foregrounds are adjusted to the correct neutral colours the blues are clearly different. Many of you may now be worrying that you have the wrong strobes; don’t. We don’t have to settle for what the manufacturers give us – we can warm and cool our strobes by attaching lighting gels to them. Lighting gels are not expensive (because they are not made to optical quality like lens gel filters) and can be bought easily from film and theatre lighting suppliers. Compared with typical underwater lens filters, the strength of filter required is very weak – to change an Inon Z240 (5500 K) to match and Ikelite DS200 or DS125 (4900 K) you need a +22 Mired shift colour conversion filter – a Lee (Number 444) Eighth CT Straw Filter is perfect and can simply be cut to fit the strobe (see the effect by clicking on image 3).

We have seen that warm strobe lighting forces a cooler white balance on the image which renders richer blues in the background. Therefore it follows that any factor in our photographic technique that lessens the warmth of the foreground illumination will reduce the richness of the blue. If we are too far from our subject the light reaching it will be cooler and the image will require warmer white balance, weakening the blue. This is a common symptom in many underwater images. Similarly if we are shooting a balanced light image and we use too little strobe on the subject (so that the subject is illuminated by a mix of strobe and ambient light) the blue will be less rich, if we try and correct the foreground colours.

So far I have only considered blue water shooting. What happens when we get into greener waters? If we use warm strobes in green water our foregrounds are again a bit too warm requiring a cooling of the white balance to create a neutral foreground look. If we cool down green water we actually push it away from green towards a blue-green colour (Figure 4, image 4).

Personally, when I shoot in green waters I like to try and record a rich green colour and warm strobes erode this. Instead I prefer cooler strobes, like the Inons. A cool strobe will require a warmer white balance setting, which will increase the greenness of the greens, producing that desirable emerald look. Again you can prove this to yourself with your own images. Open up a green water wide angle image in your RAW converter and try moving the colour temperature slider between 4300 K and 5500 K. Ignore the foreground colour and watch how much the water colour changes.

Personally I have quite a bi-polar view of the oceans many colours: I like my blues to be rich blues and my greens to be rich greens. However, many photographers diving in green waters actually like them to look quite blue. Here in the UK photographers often wait for the bluest conditions before shooting wide angle, blue water makes temperate water look particularly inviting! Either way it is important to appreciate the importance of strobe choice in this regard. If you want to enhance any blueness in your temperate waters go with a warm strobe, if you want to boost its emerald green, then a cool strobe is better.

I am certain that many of you will be reading this article thinking Why worry? I can adjust it all in Photoshop anyway. This is true, but I believe that it is important to strive to get the best possible results from the camera for several reasons. First, there is the ethical consideration of presenting images as shot as well as personal satisfaction. Perhaps more relevant today is the image quality issue. Strong individual colour adjustments either in Photoshop or even in a RAW converter are one of most damaging adjustments to image quality, introducing plenty of colour noise, particularly in gradients. Second, there is a time issue. I recently noted that my Nikon D2X had taken 93000 photos, nearly all of these underwater. Even if a colour fix takes less than 10 seconds applying it soon mounts up if you take a lot of images. Most photographers who shoot a lot soon learn to discard any images that will cost additional processing time. It makes sense to make adjustments to your shooting technique that minimise your computing requirements.

The other crucial concluding comment is that there are no rights or wrongs when it comes to water colours, only personal preference. As I said above, I like my greens to be green and my blues to be blue. That’s me, and for this reason I use my cool Inons in green waters and my warm Subtronics in blue waters. You may well be different.

When we all shot slides, our choice of film stock had an important effect on the water colours recorded in our images. These days it is the colour temperature of our strobes that has a similar effect. Neither factor makes a massive difference, but their affect is plain to see in every image we take. Understanding the importance of the colour temperature of your strobes is very much like choosing the correct film stock to achieve the look you are after. It is one of the small factors that can make the difference between getting a nearly image and the one you really wanted.

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