Focusing a shot is deciding where on the picture you want to be the sharpest and stand out from the rest of the picture. The camera can be set to auto focus or manual focus. Sometimes when using the auto focus the camera will not settle on the right part of the photo. With manual focus the operator can pinpoint the spot that he or she wants in good detail. When using the continuous focus mode the camera is constantly looking for a focus point. This is awesome for quick, east focusing but wears down the battery quickly and can wear down the camera itself.
The resolution of a shot determines how “big” your images are. The bigger they are the more detail they will show. On a lower resolution the card can hold more pictures that aren't as high quality. It may be hard to tell the difference between resolutions in the normal picture. But, when you enlarge the photograph the lower resolution shots will appear fuzzy. Because there is not much time to take a whole lot of pictures underwater, it is best to use the highest resolution. Chances are that even in this mode the photographer won't use all his or her memory.
One of the biggest advantages to a digital camera is that they can hold over 100 pictures at a time, while a film camera can hold 36 shots. Another disadvantage to film is that you have to either go get it printed somewhere or buy your own scanner both are very expensive. With a digital camera, photographers can print their pictures straight from your computer or get them developed at a convenient store. With a digital camera the photographer can see images right after they are taken.
This is essential when shooting underwater; many times you will take so many pictures with digital to make sure you have a good one. With a digital camera you can tell right away if you need to shoot the image again. On a film camera you choose one ISO speed and you are stuck with that one for the rest of the role. With a digital camera the ISO speed can be changed for every shot. Digital cameras require less light and even if the lighting is messed up you can always go back and change the colors.
Some underwater photographers still use film for a few simple reasons. The biggest one being that they are easy to use, and they don't want to have to change their way of photography after they have mastered using film. Film cameras have a longer battery life then digital cameras because they don't have a screen to waste it on. They also don't pick up dust in the water when shooting and the lenses don't fog up. Film cameras recover from a shot quicker then digital ones and can shoot back to back much faster (Jack Drafahl 14-16).
