If you practice the underwater photography with a wide angle lens behind a spherical port you will certainly have noticed than the focus distance you have to settle on the focus ring of your lens is much smaller than the real distance of the subject. This "abnormality" is due to the fact than a spherical port behaves, underwater, as a divergent lens and, roughly speaking, generates a virtual image  much nearer than the real one. It is this image that "is seen" by your camera and this explain why you have to put the focus ring of your lens on a distance around 0.4 to 0.2 meters. This problem can be corrected by using a special lens fitted on front of the camera's lens. Unfortunately this will affect the quality of the pictures and decreases the angle of field of the lens. It has to be used only on lenses whose minimal focus distance is still too big to give a sharp image of a subject even if located few meters away. This append often with zoom lenses of whose minimal distance is around 0.5 meters. With normal wide angle lenses, this distance is 0.25 even 0.2 meters. They permit to take pictures without requiring added lens. By playing with hyperfocal (depht of field), it is possible to shoot sharp images of subject quite near and maintaining a good sharpness for the back plan.

All this preamble to explain the great interest to use a lens having a minimum focus distance as short as possible . The range between infinity and 0.5 meter being unusable in our case.

The Fish-Eye Nikkor® lens 16mm f=2.8 has a focus range from infinity to 0.25 meter and Nikon® tells you that a filter (even neutral) must be installed on the rear of this lens. What append if you remove this filter ? You will  notice than the focus scale is shifted toward the short distances between 1.2 meters (when infinity) and 0.17 meter (when 0.25 meter). You have gained 32% on the short distances. This means that you can now shoot sharp pictures of even nearest subjects.

Have a nice time taking underwater pictures and comeback visit us next month.