My biggest problem with aquatic photography is trying to snap a picture while the fish are moving around like lunatics. It's as if they see me coming with the camera and say to one another, "it's HIM!!!! Maybe he has food! Lets swim up and down the glass like idiots until he feeds us or goes away!"
The other problem is the diffractive distortion caused by light traveling through water, glass, and air before it reaches the lens. I just can't get a good focus lock on any subject that is more than a few inches away from the glass. Opening up the aperture to get a deeper depth of field has no effect . This is made worse by even the most subtle cloudiness in the water.
I always forget to wipe down the outside of the tank with a wet paper towel first - result is usually a decent shot ruined by streaks and water spots. When I do wipe down the glass, the movement gets the fish all riled up looking for food again.
1 Wipe down the outside of the tank with a wet paper towel to remove streaks and water spots.
2 Turn the tank light on,but turn off the room lights to prevent distracting reflections.
3 Wait a while for the fish to get used to your presence in the room, and resume their normal behavior - the shy fish will come out, and the piggy fish will stop begging for food.
4 Use a tripod, or at least try to steady your arms on something solid as you hold the camera.
5 Try the macro setting on your camera, but feel free to experiment with other settings.
6 Set the film speed to 200 or 400. Try to use the fastest shutterspeed you can for fast fish. For plants and stationary fish, try to close down your aperture as much as you can without making the shutterspeed longer than 1/60 sec.
7 If you use the flash, shoot at an angle to prevent reflections. Try shooting without flash if you can - I find the colors are more natural and the fish's scales don't wash out.
8 If your camera has a manual focus override, use it.
9 Be patient and prepared to blow through dozens of exposures in order to get one halfway decent one. Be thankful you're not paying for film and processing.