Aperture is the size of the lens opening that can be made smaller or larger. The function of the aperture is to adjust the quantity of light entering the camera. Aperture functions just similar to the iris of an eye. The size of an aperture is known as F-stop. Each lens has a largest aperture like F2.8. The largest aperture allows the passage of most amount of light.
Aperture and F-stop are always in indirect proportion i.e. as aperture increases, F-stop decreases in number and the amount of light entering through the lens increases. This implies that a small F-stop is a large aperture and vice verse. This means that F2.8 is a larger opening than F22. Hence one must keep this aperture and F-stop relation in mind while shooting underwater landscapes where sunlight and flash both interfere.
The functions of aperture are –
- Aperture determines the brightness or saturation of the image.
- It determines the depth of field.
- It controls the amount of light, ambient light or strobe light entering the camera.
- It limits the effect of optical aberrations.
- The flash to subject distance is also determined by aperture.
- It controls the blur, also known as bokeh of the background.
Defining Depth of Field
Depth of field is a really crucial concept when it comes to underwater photography. The landscapes underwater are extensive and this is where this concept helps. The depth of field refers to the area of photo in focus. This technique is really useful to point out the center of attraction as the region outside DOF is blurred. Smallest F- stop produce a greater depth of field. This allows a larger landscape to be in focus at the same time.
Focal Point
The point at which camera is focused is known as point of sharpest focus. The depth of the field is always more than that of the point as compared to previous one. Hence the objects which are closer than this point may appear soft whereas the objects further than that will appear sharper. It is a simple fact- greater the distance between the subject and the camera, greater will be the depth of field. Small aperture gives a clear subject but the background is distracting to some extent.
Thumb Rule
While shooting underwater landscapes it is advised to keep the sharpest focus to around 1/3rd of the planned composition. This is called hyperfocal distance.