Converging lenses are used in photography to magnify an object or image. When the lens is placed under water, the curvature of the lens causes light to be bent and focused in a different location than when the lens is on dry land. The focal length of the converging lens will change as a result and some objects that would have been in focus before will not be anymore.
Focal length (in mm) = √(focal length in mm x 1.6)
Convergent lenses are placed under water to reduce the power and increase the focal length.
What is the formula for focal length in water?
The formula for focal length in water is the same as the formula for focal length without water.
When you use a converter lens and place it in water, what happens to the focal length?
If you place a converter lens in water, the focal length remains the same as in the dry condition.
More elaborately,
When the focal length of a converging lens is placed underwater, the image becomes blurry. When we have an object far away, like our eye ball, the light rays coming from the object get focused at a certain point. The distance at which the rays are focused is called the focal length of the lens. When the converging lens is placed underwater, the image gets focused far away. This means that the focal length of the lens is increased. This results in a blurrier image, and hence makes the image more blurry.
