Split Photography

I started last week trying to figure out how to create images called "Split Images" or "Over Under" shots (there is an explanation here). At first, after reviewing this site, I decided that these images are photoshoped (look at the image that is 6th from the bottom) due to the difficulty of having a even exposure over the entire image. There are apparently filters that help correct for this, and special techniques that most photographers use. So for this weeks weekly reading I found this website which is a walkthrough of how to shoot these images. He tells us that we have to use a wide angle lens, with a large depth of field to account for the index of refraction between water and air. He tells us that normal cameras just cant focus, including his own, so he made a special filter that allows for both the exposure and focus to be fixed. I look forward to trying this for myself.