Posted 07 May 2013 - 04:11 PM
When the fish is swimming around in a deep (wide) tank, it's very difficult to get the entire fish in focus. In part this is because if you rely on natural light, there's usually not enough light to shoot at a high enough f-stop to have a nice broad depth of field. If you bring in studio lights you can get around this, but then you have the hassle of more stuff to haul, set up, and power. I've used a set of 250W lights run off an inverter and car battery combo. I don't do it often because it's a PIA.
By using a sheet of plexiglass to gently "pin" the fish against the front pane of glass or acrylic, you can get the whole fish on a plane that's perpindicular to the camera, so that you can get away with a narrower depth of field. A clear pinning plate also moves your backdrop out of your field so that shadows and the background are out of focus or out of frame. Getting the fins erect is always a challenge, one that I usually cheat on, kill the fish and use a quick dip in formalin to make them stay erect! Uland and others whisper sweet nothings at their fish, or poke and prod and shoot enough images to eventually get one with the fins up. To each their own...
There's a lot of info on the process buried in the forum here... and there's nothing saying that what I (or we) do is the end-all. I still learn a different trick almost every time I go out.