Shark Photography Exposure

SHARK PHOTOGRAPHY - EXPOSURE CHALLENGES

Every image has its unique exposure difficulties.
Exposure is an equation with three variables. Stay with me, its really not that tricky. All you are trying to accomplish is to get the right amount of light to hit the film or digital image sensor. The three factors that influence exposure are: The film speed or Isometric reading - you get to choose how sensitive your film or sensor is. The more sensitive the film the faster it absorbs light. Taking fast pictures means that your rapidly swimming subject wont look like a blurred streak. Sensitivity runs between 100 ISO which is slow to 1600 which is lightning fast. Why would anyone use slow film? Because fast film speeds produce grainy images. That means that the colors are blotchy or pixilated. Digital SLR cameras let you change ISO on the fly but film shooters have to load whatever film they think they'll need before they get into the water. If its darker down there than they thought it would be, they have to sacrifice one of the other factors in the equation to compensate. Aperture - Or how big the hole is when the shutter opens. If you keep it small (like a pin hole) the image will be crystal clear as long as you keep the camera steady. That's great if you're shooting in really bright conditions. Otherwise that tiny hole wont let in enough light and your pictures will be too dark. No problem - choose a bigger aperture. Now there is plenty of light getting in but its not all hitting the sensor or film in the right place. The result is an image where the focus point is crystal clear but everything closer to or further away from the lens is blurry. This is called the depth of field. Small apertures have a very long depth of field i.e. lots of the image is in focus. Large apertures have a very narrow (short) depth of field i.e. only one distance is in focus. Aperture sizes are called F Stops. Small apertures are big F Stops and visa versa. For example a wide aperture might be F2.5 and a narrow aperture would be F20. This is done to purposely confuse amateur photographers and stop them from turning pro. Shutter Speed - this is how long the shutter lets in light before snapping closed again. Its probably the simplest concept to wrap your head around as long as you understand fractions. Basically, a fast shutter speed lets in very little light and a slow shutter speed lets in much more. Its measured in fractions of a second with 1/40th being really slow for underwater work and 1/1000 being faster that you'll probably ever use. Why not crank it way down to 1/40th and have a really small aperture and keep everything in focus? because its too tough to hold the camera steady for that long especially when your subject is swimming around. That's a whole lot of information but it condenses down to this: You want to use the slowest film speed possible, the highest (smallest) aperture possible, and the fastest shutter speed possible while still allowing enough light into the camera to freeze into a nice picture. OK, that's all well and good but it doesn't give you any real settings advice does it? That's because the lighting conditions on each dive are completely different. That's the whole reason for all those possible combinations; so that you can take advantage of different situations. What I can do is show you bunch of images and tell you what I set the camera to in each case and why. That should give you a vague starting point. Remember that you're trying to expose the background correctly with the available ambient light. This has nothing to do with making the colors show up on your subject which is done using your strobes.
	ISO 400 Aperture F8 Shutter speed 1/60th This Spiny dogfish picture was taken in the dark and cloudy waters of British Columbia. Even though the film speed is high, the shutter speed slow, and the aperture reasonably wide, the background is still a little under exposed. Because the dogfish was moving quite fast I would have liked to increase the shutter speed to get a crisper image but that would have given me an even darker background.
	ISO 200 Aperture F7.1 Shutter Speed 1/80th Shooting this close to the surface on a sunny day, I could easily have shot using ISO 100 to obtain smooth images but my old Nikon D100 didn't offer that setting. Now I shoot with a D2X which does.
	ISO 100 Aperture F10 Shutter Speed 1/60th Nice bright conditions at the surface allowed me to shoot on my slowest film speed, but I still needed a fairly slow shutter speed to gather enough light for the water to expose properly. My strobes were set on high so that the shark would not be just a silhouette against the brighter surface.

	ISO 200 Aperture F11 Shutter Speed 1/80th This ghost shark was shot in 110ft in the semi darkness. If it had been in mid water the background would have appeared completely black but its proximity to the reef allowed me to expose the background nicely with my strobes.
Maybe that gives you a feel for some approximate settings but you don't have to guess your exposures. Lots of digital and film SLR's come with built in light meters and you can buy separate ones for those that don't. The technology is complicated but using one couldn't be simpler. All you have to decide is which part of your image needs to be exposed correctly. If you are shooting a shark in the blue then you want a nice blue background and not a shark in the dark. So assuming you have an SLR with a menu, set it on manual and point it at an empty area near the shark. When you half depress the shutter button and look through the view finder you should see a gauge that tells you if your image will be under or over exposed. Often this is displayed as a rule with minus at one end and plus at the other. Now you can play with your aperture and shutter speed until the display indicates that you are on zero (half way along the rule). Now your water will be blue but only if you shoot in that direction. If you move around the light will be different and your settings need to change. Note: your reading will get screwed up by the sun if you're pointing straight at it so make sure you're pointing at the most neutral area of the water with regards to brightness. Ok now you should have your background exposure dialed in so all that you need to do is light your subject correctly to bring out the color. If you're unsure how to do this go back to strobe use for a reminder.
	Creative exposures. Like most aspects of photography you can break the rules and end up with some pretty cool results. This Lemon shark image has a blown out background creating a sharp contrast with the shark. Its tricky to make this work because of the shark's white belly. More often than not you will end up with a half visible shark, but if you're shooting digital you can afford to play around and delete later. The important thing is to light the shark well. A silhouette shot in water this shallow is more likely to end up looking like your strobe failed than artistic. You want to over expose the background just enough to turn it almost white but not so much that it begins to flare. And, you need to crank up your strobe to expose the shark at the same level as the sky.

Bracketing: What your internal light meter thinks is a good light level might not look so good when you download your pics. Also, they aren't really designed to work underwater although it shouldn't make that much difference. To make sure your exposures are correct you can take extra pictures of each shot that are 1 or 2 F-stops higher and lower than your light meter deems appropriate. This is called bracketing. There are obvious drawbacks to bracketing especially for shark shooters. Firstly, you'll run out of film or memory space three times faster, and secondly, most sharks wont stop swimming to wait for you to adjust your F-stop. I don't do a lot of bracketing. I rely on my review screen that shows me a histogram of my digital image. It shows me if any areas of my picture are completely blown out. Be careful when using this as your reference because the back lighting on these little screens often make your images appear brighter than they really are. If you're more or less on the money, a little tweak in Photoshop will help you get it looking just right. If you are shooting in RAW (a file type available in all new DSLR cameras) the camera will gather more information than you can see just by reviewing the image. So, in photoshop you can bring out the hidden over or under exposed info until your image looks how you intended it to. There are limitations; you can't turn a black picture into a brightly lit masterpiece but the RAW file capabilities will certainly help with minor adjustments. Many pro shooters still bracket believing that its better to be safe than sorry.
In a Nut Shell: Choose the right ISO for the dive. Try to use high F-stops to increase your depth of field Try to use fast shutter speeds to avoid blurry sharks Train your light meter on a neutral part of the background Set your Digital SLR on RAW if you have that option If you cant review your images, bracket Andy Murch works as a Photographer for Shark Diver Magazine. BACK TO SHARK PHOTOGRAPHY MAIN PAGE HOME LINKS TAXONOMY UNDER THREAT BOOKS CONTACT