Over-Unders / Split Shots
By David Doubilet
Pictures made half in and half out of the water should be called “half and half” pictures, not splits or over-under images. Splits refer to a dessert involving a banana. This technique brings together the two worlds of air and water and when done well they can be compelling - but there are rules.
First Rule: Go big
You need an SLR camera with a very wide angle lens. Something on the order of a 14 mm, 15mm or fisheye lens will do. The lens is not enough; you will have to have a very big dome to mount on the camera housing. Big means a 7 to 8-inch diameter dome.
Second Rule: Both the over and underwater parts need to be interesting
Both the underwater and topside halves of the image need to be interesting or you have a boring non-picture. The reason we see so few really good over-under images is because there are not loads of opportunities for incredible topside with magic happening below the waterline. I think this is why we see so many pictures of divers swimming in blue water under a live aboard dive boat at high noon. Take your time and look at your surroundings. If I think something might work I try it. Failures are ok; always better to reach for something.
Some of the best split shots are made in shallow water - if you can stand, even better. Your lens will see the bottom and the surface of the water, adding a nice dimension. If you can’t stand up you can create a human bobbing monopod by inflating your BC to the max and resting your housing on it. If you are in a current forgeddabout it, go find a school of fish.
Third Rule: Be aware of the difference in focusing between air and water
Over-under images involve complex optical problems that luckily have simple solutions. You must remember this for the bottom half of the image: water magnifies objects by 25% when looking through a flat window like a facemask or flat port. Girls tend to hate this effect because their legs look bigger in the water. A dome corrects for this magnification. A dome is really in essence the rear element of an enormous lens called the sea. It produces a “virtual image’ that floats 18 inches in front of the dome. So now your wide-angle lens must focus to 18 inches. The optics of the dome does not affect focusing in air so infinity in air is still infinity. You can correct for this difference in air and water by using a half-diopter, or better yet in the era of digital we can stop the super wide-angle lens down to f/16 or f/22. The increased depth of field from the high aperture should now take care of the difference in focusing in air and water.
Fourth Rule: It is all about light
In simple terms the surface is bright and the bottom is dark. A brilliant white sand bottom is a gift but most of us find ourselves elsewhere and using strobes to light the underwater subject. And on occasion I use a graded neutral density filter over the “air” side of the lens.
Fifth and Final Rule in the World of Half and Half Images: Water droplets
We don’t want them and they don’t have to be there. Laugh, but I use lemon pledge to clean Plexiglas domes to get rid of greasy finger marks, small scratches and goo. Do NOT use this on glass domes. And finally when you are in the water and about to make the BBC underwater picture of the year, remember to dunk the dome quickly and smoothly to get rid of droplets. Photoshop is not the answer to this problem. More dunking, fewer droplets, less Photoshop.
The bottom line is this: Half and half images are not easy and they take time and concentration - but they used to be worse. The digital camera has made our lives easier with instantaneous feedback. Now we know when to quit and chase a school fish.