Though an action camera is equipped with ultra wide lens, its coverage underwater will dramatically narrow down due to different refraction ratio between air and water.
For example, maximum angle of view of GoPro® HERO13 Black is approx. 156° on land which will narrow down to approx. 94° when we put the camera in genuine dive housing and bring it underwater due to different refraction index. The INON UFL-GR140/UFL-G140 provides ultra wide semi-fisheye imaging with angle of view 140° underwater enabling wild underwater video work only with action cameras.

 
* Measured angle of view by INON or calculated angle of view underwater based on the measured angle of view. Not confirmed by camera manufacture. The measured angle of view of “HERO3+ Silver Edition” is approx. 142°(air) which is less wide than the “Black Edition”. So angle of view underwater with this lens is less than 140°. The “HERO3+ White Edition” has not been tested.

Shooting through the INON UFL-GR140/UFL-G140 lens enables you to shoot a subject at close range to benefit deformed and/or perspective result.
The native depth of field (DoF) of the GoPro®HERO13 Black on land is approx. 60cm/2ft to ∞. With the INON UFL-GR140/UFL-G140, DoF underwater will be extended ∞ 4cm/1.6in to ∞ closer to camera side.
 

* DoF on land is based on focal length/aperture of camera lens and pixel pitch of the image sensor. DoF underwater is measured from "the forefront of the lens".

Both UFL-GR140/UFL-G140 lenses are optimized to produce quality images from the minimum focusing distance to infinity. A 5-layer multi-coating on the inner surface of the acrylic dome ensures excellent image quality comparable to that of a glass dome, while keeping budget price.