## Exercises

Most of the exercises with different lens types will come later on in the course once we have discussed composition in a bit more depth. However, there is one subject that needs addressing here if you are using a viewfinder camera.

Close-focus wide angle is a very valuable technique in your underwater photographic repertoire, however it does need you to fully understand the features and limitations of your lens.

1. Look up your wide-angle lens technical data and find out what it's minimum focusing distance is.

2. Now calculate what it's real minimum focusing distance is when we take depth of field into account.

1. Find yourself a flat subject with fine detail in it. An underwater diving slate with writing on it is ideal - use your submersible tables slate or something similar.

2. Go into the swimming pool with your camera and lens. You must do this underwater.
• Starting with your maximum aperture (f/5.6 perhaps).
• Write on the slate, in chinagraph pencil, the aperture that you are using.
• Set up the slate at the stated minimum focusing distance, flat on to the camera, and write on the slate the distance that it is at.
• Take a shot.
• Move the slate closer by one tenth (if you started at 1 metre, move the slate to 0.9 metres away), write the distance on, and take another shot.
• Repeat another 3 times (at distances of 0.8, 0.7 and 0.6).
• Repeat the above for each aperture setting on your camera, f/8, f/11, f/16 and f/22.

3. Get the developed, and examine each frame for sharpness. From this you should be able to determine how close you can get at any particular aperture, and still have the subject in focus.

If you are using a supplimentary wide angle lens - one that screws or bayonets onto the front of your prime or standard lens, then there is an additional exercise for you.

1. Look up your wide-angle lens technical data and find out how to set it up. Usually it will tell you to set your prime or standard lens to its infinity setting. If this is the case then ....

2. Set the prime lens to it's minimum focusing distance, and repeat the picture taking exercise above at this setting. You should find that you can get a bit closer to your subject.