So now you’ve got a camera, you’ve made a lens choice, you’ve selected your ISO, and you’ve got an understanding of the relationship between shutter speed and aperture. Are you ready to make pretty pictures underwater? Almost. But first, we’d better fire up your flash.

You may remember being introduced in your basic scuba class to a guy named Roy G. Biv. He’s fictional but gives us a reminder of the way colors “disappear” as we go underwater: Red, Orange, Yellow, Blue, Green, Indigo, and Violet. But the basic concept to walk away with is that if you want to see color underwater, you need to have a light shining on whatever it is you’re looking at. When we deal with that photographically, that means we need to have a strobe or flash of some sort to get color into our pictures. (The terms “strobe” and “flash” can be used interchangeably.)

Flashes can be thought of in two ways—on-board flashes that are part of the camera, and stand-alone flashes that are separate from the camera itself, and which usually mount via a strobe arm to the camera or camera tray. Either one will work and both have pluses and minuses.

The biggest plus for an on-board strobe is that it’s already part of the camera so you don’t incur any additional expense. And since it’s matched for your specific camera, it’s probably going to work pretty well in an automatic or TTL (through-the-lens) metering mode. But there are some definite drawbacks to an on-board strobe too.

The most noticeable will be backscatter. This is what happens when the strobe is positioned very close to the camera lens, and there’s particulate in the water between the camera and the subject. When the strobe fires, it lights up the particulate, which then reflects back into the camera lens and shows up as spots all over your beautiful picture. The only way to get rid of this is by moving the strobe away from the lens, and that’s simply impossible with a built-in on-board strobe.

The other drawback is the power (or lack thereof) of the strobe. Generally, on-board strobes simply aren’t too powerful. On top of that, since they’re running off the same batteries that power the camera, they’re going to drain the battery life more quickly as well. This can especially be an issue for digital camera, where the batteries are controlling the camera, the LCD screen on the back, and the on-board strobe.

The other option is to go with a stand-alone off-camera strobe. Advantages here include more power, a wider angle that the light covers, no drain on the camera battery power since they run on their own batteries, and an opportunity to be creative with your lighting since you can light head-on, from the side, from the back, or at pretty much any angle you like. (You can even add a second strobe, as I do, to give yourself more creative and balanced lighting since now you’ve got light coming in from both sides of the picture.) But there are drawbacks as well.

The first one is expense. Strobes aren’t cheap, running anywhere from a few hundred dollars for small models to close to a thousand dollars for more powerful, larger versions. Then you’ve got to add in the expense of the strobe arms, cables, and a mounting tray to attach both the strobe and the camera to. (And if you want to shoot with two strobes… double the expense.)

The other disadvantage is that, despite being the favorite phrase of Tim the Toolman Taylor, “More Power” isn’t always a good thing underwater. It may simply mean that you can more easily over-expose shots. Plus you’ll find that the things that can now go wrong having seemingly multiplied when you add an off-camera strobe. I have one flash that other divers see me occasionally smacking with my hand. “What were you doing?” they ask. “Trying to get the strobe to turn on,” I glumly say.

There are also issues of whether some strobes will work with some cameras in TTL, dTTL, or iTTL modes. If they don’t, it simply means you have to shoot with the flashes in manual mode (which is not much of an issue with digital cameras since you can see the results right away). Still, other strobes may not work with certain digital cameras because the camera fires a pre-flash and the strobe lacks the ability to ignore it and fires, out of sync with the camera.

So no matter how you go, there are pluses and minuses. But there’s also no question that adding a strobe will give your pictures that eye-catching appeal and “pop” that makes people go “Wow!! Did you take that?” And how do you get to that point. Well, it takes a bit more than just adding a strobe. And we’ll cover that in our next installment.