Basic Shutter Speed, Aperture and Depth of Field Underwater
Although shutter speed, aperture, and depth of field
are at times difficult and confusing to understand. Mastering these basic
concepts and how they relate to one another will greatly improve your
Shutter speeds are
expressed in fractions of a second that the shutter is open: 1/30, 1/60,
1/125, 1/250, 1/500, and so on. 1/30
means the shutter is open for one thirtieth of a second.
Notice how each fraction is doubled from one shutter speed to the
next, or decreases by half, respectively; indicating that the shutter
remains open twice as long, or closes in half the time.
shutter speed does two things.
If your shutter speed is 1/125 and you change the speed to 1/250 you have just decreased the amount of light entering your camera by half. If you went down to 1/60 you would be increasing the time the shutter is open by double and allow more light into your camera.
2. You can use shutter
speed to “stop” action: The quicker the action, the higher the shutter
speed needs to be in order to freeze that action.
Most fish and marine life can be freeze framed with a shutter speed
of 1/125, but sharks, seals and dolphins who are known for their speed,
are best shot at faster shutter speeds; 1/250 or better.
Aperture / F-stop
Aperture sizing or openings
are expressed in values known as f-stops; common f-stops are: f2.8; f-4;
f5.6; f8; f11; f11; f16; f-22. As
with shutter speed, f-stop openings decrease by ˝ with each step. If an
aperture setting is f8 and you change to f11 you have just decreased the
aperture opening size by half. If
you were to go from f8 to f5.6 you would have increased the opening by
twice the size – admitting twice as much light.
Where people get confused by f-stops is the concept of big and small. It seems like f22 should be a larger opening than f8. But the opposite is true. That’s because f22 is shorthand for f 1/22nd and f8 is shorthand for f 1/8th.
Aperture Has Three Functions:
Depth of Field
Aperture settings determine what your depth of field in any given photograph will be. The widest aperture, f2.8, will give you very shallow depth of field. Conversely, the smallest f-stop, f22, will create the greatest depth of field in a photograph.
Keep in mind that depth of field is also affected by the focal length of the lens; the shorter focal length of the lens the greater the apparent depth of field. For example, a 19 mm lens will have a much greater over all depth of field than a 100 mm lens.
Getting it in Focus
Another important point is
that the greater the distance from the camera to the subject the greater
the depth of field. On the
other hand, the closer the subject is to the camera’s lens, the lesser
the depth of field. That’s
why depth of field is so shallow in macro photography.
One Final Rule of Thumb