Photo Clinic, Part 5

Flash:
     If you're taking underwater pictures, you need a flash. There are exceptions. I got some very interesting pictures using natural light with a pink filter and superfast film in an algae-filled reservoir. And some of the best garibaldi pictures I've ever taken were done with Kodak 800 Max film and a red filter, using only ambient light. But the rule is:  whether your picture goes on the wall or in the trash depends on how you use your strobe(s).
     Your strobe's TTL setting can usually provide decent exposures. It fails, however, when you have a small object on a dark background, or when using a wide-angle lens. In these circumstances you should switch the strobe to manual and calculate the f-stop using the strobe's guide number.

Many strobes have an "exposure guide" printed right on the side. The table gives the appropriate f-stop for proper exposure at a given distance. If your strobe is set on TTL, that distance is the MAXIMUM space you can allow between you and your subject. If you have two strobes, you have twice as much light, but NOT twice as much distance! Go up one f-stop.

     Guide number divided by distance equals f-stop. So to take a picture of a diver at arm's length (3 feet) with a guide-number 32 strobe, you calculate 32 / 3 = 10.6. You set the aperature to f-11 for the perfect exposure. Of course we're using the non-metric scientifically-illiterate American measuring system here. If you use metric, adjust accordingly. But on with the lesson. Repeat after me:
                   Guide number divided by distance equals f-stop.
                   Guide number divided by distance equals f-stop.
                   Guide number divided by distance equals f-stop.
                   Guide number divided by distance equals f-stop.
     Guide number divided by f-stop equals ideal subject distance. For a "diver descending through kelp" shot, for example, you get the perfect ambient light exposure at f-8. With a guide number of 32, you calculate 32 / 8 = 4 feet. So you fire the picture as he reaches the spot 4 feet above your head.
     "Bracket" your flash pictures. Repeat the picture with the aperature set one f-stop below, and again one f-stop above your calculated setting. If the calculated setting didn't give a good exposure, chances are one of the repeat shots will. If you're shooting on TTL -- for example, with your macro extension tube -- bracket your picture by changing the ASA setting of the camera to half the true value, then twice the true value (for a total of three pictures).

The effect of fill-flash: I was shooting Gary as a silhouette against the flare of the sun when he dropped down below the sunspot. I turned on the strobe to change picture styles. With the strobe, his face and eyes are now visible. This type of picture makes his mother happier than a simple black outline. Gary Argyle at Isthmus Reef, Catalina Island Nikonos V w 20-mm lens, two YS-50 strobes

     "Fill-flash" pictures are best for larger subjects. Fill-flash means exposing the film based on the ambient light, but adding a flash to highlight and improve the color in foreground objects. Some cameras can do this for you automatically -- sometimes. For example, putting the Nikonos V shutter knob on "A" for "aperature priority" and switching the strobe to TTL, will usually give you a reasonably balanced picture, provided the foreground object is large enough. For more control (and more predictable results, assuming you do it right), set the aperature manually after metering the ambient light. Put the strobe on TTL.
     With the Nikonos V, you can "bracket" the TTL shot by changing the ASA setting on the camera. For example, with 100 ASA film, shoot two more pictures -- one with the camera set at 50 ASA and one at 200 ASA. This can give you more, or less, effects of the strobe when compared to the background light.

If at all possible, you should shoot your ambient-light photos near the surface. The shallower you are, the richer the color. You'll rarely get a good "fill-flash" shot below 30 feet. In the kelp, you need to be even more shallow. So find a spot on the reef at around 10 feet, use your 20-mm lens, and it will look like you're 30 feet down. The garibaldi at left was shot at a depth of 6 feet.

Double strobes make your pictures look Pro. You can get good photos, like this photo of a juvenile garibaldi, with a single strobe. But think how much better this picture could be if a second strobe illuminated the right side of the garibaldi. Compare the harsh shadow on the right side of the garibaldi to the much softer shadows on the sulfur sponge in the picture below. Go back to the previous lesson and look at the hermit crab. How would that picture look if the right side of the shell were illuminated? Juvenile garibaldi picture taken 1992 by Steven Argyle Nikonos V 35-mm w closeup lens, single YS-50 strobe

In this picture of a sulfur sponge from the previous lesson, the right strobe stays on the camera, providing an even fill. Meanwhile, the left strobe is taken off the mounting tray and held closer to the sponge, illuminating it from the left. This gives fuller colors, more of a sense of depth, and is more visually interesting. Sulfur sponge, Catalina Island Nikonos V w 1:1 extension tube, 2 YS-50 strobes

For most photographers, the easiest way to get even illumination is to buy a slave strobe. This strobe fires when it "sees" the light from your main strobe. The slave strobe should usually be used for "fill," evening out the illumination, while the highlights are lit up by your main strobe. It's usually best to use a slave strobe that's around 1/2 the power of your main strobe. You can buy slave strobes with TTL function (so they shut off when the main strobe turns off). When using a slave strobe, you may need to experiment a bit to get the right balance of light for your closeup and macro shots. Slave strobes can be used for special effects, such as backlighting behind a sea fan or illuminating the inside of a shipwreck. Slave strobes can be useful in silty water: have your dive buddy hold the slave directly above your subject, and aim your main strobe high -- so light hits the slave's sensor, but doesn't hit the subject.

If you use two balanced strobes, connected by a sync cord, balancing the light is simpler. Because the strobes have matched output and will fire (and stop firing) simultaneously, you simply move the strobes to balance the light. If you want a strong highlight from the right, you move the left strobe further away from the subject. This is more intuitive than using a slave strobe, but the cost is higher, and the cords prevent you from using your second strobe for special effects.

"Edge illumination" is a useful trick. Get the strobe away from the camera, then aim your strobe so the EDGE of the strobe's output just covers your subject. The goal is to have NO light hitting the water between your camera lens and the subject. (The haze of illuminated water dims the colors in your photo, and particles near your lens will create white blobs in your picture.)

This picture is an example of how particles in the water can ruin a picture. Taken with an MX-10, the strobe has hit tiny particles near the camera. These brightly lit particles are out of focus, and tend to assume the shape of the aperature opening (which, on the Sea&Sea cameras, is square). The colors are muted, because microscopic silt particles have been illuminated, making all the colors milky. With the MX-10, you can't move the strobe, so your photo options are limited when there are particles in the water. Using a 20 mm lens and shutting down the aperature helps control the effects of particles in the water. Bluegill in Blue Lake MX-10 w YS40 strobe, standard 32 mm lens

For these cameras, shoot with a fast print film, such as Kodak 400 Max. Shut the aperature down accordingly (to f-8 on the MX-10). Your strobe will now seem 4 times as powerful, and the smaller aperature will let you get closer to your subject while keeping the focus crisp.

About cameras with internal strobes... Suppose you've attached a strobe to a Seamaster Pro or an MX-10. These cameras also have their own strobes in the camera body. Do you want the camera's internal strobe to fire, too? No. Or maybe. For most photos, you want to suppress the internal strobe so it doesn't light up the water in front of the camera. That means you DON'T use the flash settings on these cameras -- or both the external and internal strobes will fire. And the internal strobe will light up the water in front of the camera.

On the Seamaster's shutter speed control (left) the "lightning bolt" setting sets the shutter to 125 and uses the camera's internal flash. On the MX-10 (right) the aperature wheel has two settings, f-4.5 and f-11 in orange, that trigger the internal flash. All other settings will use only the external flash.

On the Seamaster, you may want to use the internal flash for the 2T macro lens. That's because the framer is so close to the camera body that the external strobe will be almost directly overhead. If your photography conditions prevent you from moving the external strobe, you may get better pictures by using the flash setting.

With the MX-10, you can experiment at the f-11 flash setting when using the macro framer, to see if having two light sources gives you smoother illumination. Caution: at f-11 your depth of focus is not great, so you may have blurry pictures.

Click on the garibaldi for the next lesson. Click the left one to go back.

About the author: Bruce Argyle is faking this article, because his only training in photography was a course at Water World Divers 7 years ago. It just goes to show that anyone, even someone as mentally slow as yourself, can master scuba photography.