FIT +16, Subsee +5, Inon UCL-165 확대율 테스트

It is important that underwater shooters understand that the strength of a given lens is not absolute. Let me explain:

The dioptric strength of a lens (+5, +8, +16, etc.) is relative to the medium that the lens' refractive surfaces contact (air, water, jello, etc.). So, while these FIT lenses have strengths of +5 and +8 in air, they appear to be water-contact lenses (correct me if I'm wrong!). If so, they are not +5 and +8 underwater, because typical glass achromats lose around 60-70% of their power underwater.

Timmoranuk - By direct measurement from the photos that Alex has provided, the magnification ratio achieved by the +5/+8 combo relative to the shot with no diopters is about 1.5:1. That's what you would expect from an underwater +5 diopter lens. This is consistent with the loss of strength due to water contact mentioned above. If this is true, then the FIT +8 is an underwater +3 (same power as the Inon UCL-330), and the FIT +5 is an underwater +2. A similarly constructed +16 would be an underwater +6 diopter lens (same power as the Inon UCL-165).

The MacroMate and SubSee are examples of sealed optics which retain their power both above and below water, since the lenses are always in contact with air.