In the last “Underwater Photography Series”, Part 4, we covered some of the basics about shooting using available light. In this post, we’ll be talking about how using a flash changes the equation. We will also cover some of the basics of using a strobe, like positioning the strobes to produce the best picture. Photography while scuba diving cannot realize it’s ultimate potential unless we master the Strobe!
The primary advantage of using a strobe is that it adds back the light spectrum that was lost as we scuba dive into deeper water. That enables us to capture all of the magnificent color that is difficult to get as we go deeper. As this picture of Capt Scott diving on the Wreck of the Duane off Key Largo shows, it’s difficult to believe the beautiful color in all of the coral at 100ft. But, strobes bring with them their own set of issues.
The first is that the power of the strobe to light the subject falls off very quickly. In fact, to be technical, the power of the light is inversely proportionally to the square of the distance. Probably it’s easier to understand looking at a diagram.
2 ft away, the light has 1/4 of the power it had at 1ft and at a distance of 3ft it only has 1/9th of the power! So if you are using a strobe, the golden rule of underwater photography is even more important. What’s that I hear you ask?
Rule 1 – Get close to your subject
Rule 2 – If you think you are close – get closer!
The next issue that comes with using a strobe is that the light doesn’t only illuminate the subject that you are interested in, it can also light up the small particles in the water. This is called backscatter and is the bane of the underwater photographer. This is caused by improper positioning of the strobe. I wish I could say that I had to look hard to find a good example in my library, but, if I did, it’s only because I threw out several hundred pictures that had that problem.
In a future post I will talk about ways to overcome backscatter and tricks for shooting in bad visibility. I’ll even show you ways to take it out of a picture by using the magic of Photoshop.
If the strobe is pointing directly at the subject as shown in the left hand diagram, all of the particles between the lens and the subject are being lit as well. If however, the strobe is further away from the lens and aimed so that the flash doesn’t light the area between the lens and the subject, then less of the backscatter will be lit and it won’t show up in the picture. That is one of the reasons that people use extension arms to move the strobes away from the lens and allow them to be aimed away from the subject.
Strobes produce areas of strong light in the middle of their beam. These are called “Hot spots”. When you position your strobes, you need to pay attention that any hot spots are not coming through into the picture. You can generally do this by making sure that the strobes are positioned behind the plane of the port.
Flash Diffusers are commonly used to increase the beam angle of the light. This helps in getting good light coverage when taking wide angle photographs. It also “softens” the light and avoids some of the harsh shadows that can otherwise occur. An additional reason to use a diffuser is to reduce the glare from a highly reflective surface , like this shiny Barracuda. But, like all of the other things we’ve talked about, diffusers can sometimes be a disadvantage. If there are a lot of particles in the water, then they can add to the backscatter problems we talked about earlier. If you’re lucky enough to be diving in the clear waters of Key Largo, this isn’t usually a problem, and you can put the diffusers on and forget about them.
The next question is how many strobes do you need? The answer to this is fairly subjective. A lot of photographers, even though they may have two strobes attached to their camera, often only use one of them. The purpose of the strobes is not to blast the subject with light, but as I said earlier, to add color spectrum.
If you hit the subject with too much light from every direction, all the shadows will be eliminated. This leads to a flat, uninteresting picture. A second strobe can be used for a variety of purposes. It can be used to fill in light to avoid harsh shadow in a macro photograph where the strobe is very close to the subject. It can increase the area of coverage in a wide angle picture, and it can be used to achieve interesting lighting effects.
The second strobe is often referred to as a “fill” light and can be smaller than the primary strobe. Having said that I would recommend that, if you are using 2 strobes, use 2 from the same manufacturer. This can avoid some of the connection problems that are sometimes encountered when trying to mix strobes from 2 manufacturers on one sync cord. As you can see from this photograph of 2 Butterfly Fish taken while scuba diving Key Largo, 2 strobes can create the perfect “blend” of light.
In the next chapter, we will be talking about how to take advantage of the best of the available light and blend it with your strobe light to create your optimum image by using them in combination. We will focus on the creative alternatives available to the scuba diver/underwater photographer to produce an image that conveys the feeling as well of the detail of the photograph.
See you for the next installment, and happy scuba diving to all!
Sea Dwellers Dive Center Instructor Dave Jefferiss