As a prescription lens wearer, I've always had to wear some type of Rx mask to be able to see underwater as I do on land with my glasses; I wear progressive bifocals with small lenses low in my mask. When I saw the HydroOptix MEGA mask, which allows nearsighted users to see clearly underwater without an Rx, I had to investigate it.......
HydroOptix MEGA -4.5d mask
The mask's main feature is view-through-refraction correction of light underwater and correction for nearsightedness through negative power diopters. The polycarbonate dome lenses approximate a -4.5 diopter correction for a wide range of nearsighted divers. As the diving population ages and more people wear contacts or glasses, this makes sense from a customer base perspective. Those with 20/20 vision wear disposable contacts that make you temporarily nearsighted. While this sounds crazy, the enhanced field of view of the MEGA -4.5d is so dramatic that this small adaptation is warranted. The manufacturer has a test you can perform on their web site to determine if you can use the mask without contacts. There is also a less extreme -3.5d lens being developed.
The mask has two large Twin-Turbo purge valves located low under each lens. These clear any water sloshing around with a gentle puff. The mask skirt is available in opaque black or silver silicone.
Tests with prototypes proved that due to the increased amount of vision the MEGA -4.5 mask provides that clear skirts created light bouncing around and was distracting. Underwater photographers usually like dark skirts anyway to allow concentration on viewfinders or LCD screens.
Also offered are "Buddy Holly" or "Harry Potter" style colorful and durable glasses with fixed Rx diopters, which you can use on a dive boat before and after dives. Additionally there is a "snap on" Rx lens that clips on the mask frame (for topside use) which you can stow in a "frame" once underwater -- a well thought system to enhance your use of the MEGA mask.
Diving with the MEGA -4.5 d mask
Before you use the mask, you must clean the polycarbonate lens with a mild detergent like DAWN dishwashing detergent or Simple Green solution. Neither of these will scratch the polycarbonate lenses. NEVER use toothpaste or other abrasives on the lenses. Any scratches on the outside of the mask will simply be filled with water. Like on acrylic housing ports, these will not be visible while underwater.
This mask is not a small volume mask, and because of this I was originally reluctant to even consider it. However, on scuba this wasn't really a problem for me. I'll be trying it on my next trip where I can snorkel, too. The skirt is so comfortable it doesn't feel like those giant "aquarium" 3 window large volume masks from years ago.
After the DEMA show in Miami, I went diving in Key Largo, FL. After a flat calm ride, my buddy Lazaro Ruda and I descended in 22' of water with 60+ feet of visibility. Immediately upon descending, my vision was equivalent to looking through a wide angle lens! The peripheral vision is so enhanced underwater that I felt as if the space I was swimming through was very large. One obvious adjustment was to realize that I was now seeing in "real" corrected distances. Knowing where your fins actually are was one thing easily adapted to after a dive or two.
Shooting with my Ikelite housing with Nikon D100 camera, I was able to see the viewfinder and settings easily. The curved lenses did pick up some scratches from my housing viewfinder, and the distance to the eyepiece was increased slightly from my flat window mask. Digicam shooters and videographers who frame with a LCD screen will likely think the mask enhances their shooting due to the increased field of view.
At one point, Laz and I had our heads looking down in the reef when a movement from the top view of the MEGA mask caused me to look up. Barely twenty feet away was a 8'-9' hammerhead doing figure 8s, after having just chased a stingray under a coral head. I immediately signaled Laz and took off towards the shark, trying to adjust my zoom lens for a shot. Even though the shark was turning away, I'm convinced I never would have noticed it without the increased vision of the MEGA -4.5d mask.
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