Are standard camera glass/UV filters waterproof?

[DazedAndConfuzed]

No. The underwater +6 is a +6 because it has airspace and dual lenses. The wet single lens is surrounded by water, which has it's own natural refraction negating the effect of the lens. The underwater lens is also designed to be watertight, is coated to prevent salt corrosion and uses a fitting that is generally anodized as well to prevent salt corrosion. My Subsee +10 is about 2" long and quite heavy to prevent it imploding under the pressure of 3-4 atmospheres at 60-100 feet or more.

I know the subsee +10 has flat plane glass on both ends to allow it to maintain its above water focal length. But what about the Inon and many other closeup lens. From looking at them, they all seem to have a spherical front lens, thus they have their magnifying lens in contact with the water, decreasing their diopter power, although the rear of the lens looks flat, thus it could have have 2 lenses with 2 curved front, with one of them in contract with the internal air chamber.

Are they listing the diopter power/focal length in underwater settings?

Looking at Inon's tests:

INON Close-up Lens UCL-165M67 [Overview]

They get down to 1/2 the image size (what they call 'shooting distance', ignore the working distance, since it could be skewed by the actual wet lens attached in front of the camera, and the single or dual UCL330 number don't correspond) with 1 UCL165 or 2 stacked UCL330. That means a +4.5 min working distance of the telephoto settings becomes +9, thus the UCL165 has a +4.5 underwater diopter capability and the UCL330 is +2.25