Notes about things regarding scuba diving that I have come to know.
YOUR DIVE MASK
Selecting
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Purge
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Correction
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Cleaning
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Defog
Selecting a Mask
Your mask is probably the most critical fit item of your entire dive gear collection. A poorly chosen mask will not consistently provide a clean dry air space in which your eyes can focus. A leaking mask that you need to repeatedly clear will add to task loading. As you start to do things such as carry a light on a night dive, manage a dive flag or control the air in a drysuit you do not need to be fussing with your mask. In addition to not leaking the lenses must remain clear of foggy condensation. Most serious dive incidents occur when a series of things go wrong. Don't let you mask be part of an incident history.
Modern dive masks are generally made in a goggle format where the eyes are in a major space and the nose is in a connected compartment. The two spaces are connected so that when you exhale through your nose air will fill the eye space and displace water thus clearing the mask. The nose space is a thin pliable form that allows you to pinch your nose when performing the Valsalva maneuver. The skirt may be a clear silicone or a black silicone. The clear will admit more light sometimes relieving a sense of claustrophobia. The clear material will usually yellow over time though not to any detriment. A black skirt will block out extraneous light and they are preferred by photographers and enjoyed by many who prefer not to have stray light bouncing around.
In addition to the primary lenses many masks have additional lenses to add to your peripheral vision. You may not clearly see anything through these but they are sometimes enough to confirm the presence of a buddy to your side without turning your neck. Some masks have lenses that extend downward and lay in close to your cheeks. These can help you see the gear on your chest and can be convenient. Don't let this be a crutch. You need to know your gear by touch in any case.
Be sure to get a mask with a nice broad strap. I have seen some with very narrow bands of silicone and they look scary. Be sure to get a spare strap for your save-a-dive kit.
The big trick is to confirm that it will seal comfortably to your face. This is best done with your regulator mouthpiece in your mouth, a snorkel is better than nothing. The reason for the mouthpiece is that it will modify the contour of your face. Take a mask of interest and with the straps out of the way press it lightly to your face as you hold your breath. An exceptional fit will grab like a suction cup. The next level is to inhale lightly as you put the mask to your face, will it hang on easily? Don't inhale forcibly, that won't prove anything. As you try different masks the differences will become apparent. If you have not tried litterally dozens of masks don't say,"I tried everything".
Vaseline is said to help with sealing over a mustache. Laugh lines can be a challenge.
As you get your mask in the water for a real test be certain not to over tighten the strap. If too tight the skirt will be splayed out and it won't function correctly. More mask problems have been solved by loosening the fit than by tightening.
Purge or Not
Some masks have a purge valve. This is a one way flow valve (check valve) integrated into the nose cavity of the mask. These masks are designed to relive the diver of some of the technique required to clear a plain mask. They are easier to clear and are an easy sell to new divers who feel challenged by the mask clearing skill. In my opinion this is a feature you will be better off without.
First of all if you intend to venture down deep into the depths you really want to be comfortable enough with your skills to not need this feature. As you gain just a little pool time you should find (with good instruction) that you can clear any mask without difficulty. With a little pressure applied to the top of your mask the skirt in effect is a purge valve so just have at it.
Second, consider the design and placement of the valve. The valve is usually a little silicone wafer attached to a plastic support cage. The cage in mounted in the nose pocket that you will be squeezing to help equalize pressure in your ears. It is inevitable that the valve will eventually tear into the nose pocket, ruining the mask.
In general "that's my story and I'm sticking to it" as they say. However scuba gear is adaptive gear and everyone's adaptation is unique. If a diver has limited range of neck motion then positioning a plain mask for effective clearing can result in some disruptive whole body gyrations. In this case a purge valve has unique value and is well worth the trade-offs.
Will you die if you dive with a purge mask? Heck no. I just think I can do better things with the extra $5 or $10 and get a more durable mask as part of the deal.
Vision Correction
Many divers wear prescription eyewear topside and that need follows you into the water. The first thing is reading your instruments. If your eyesight does not allow easy reading of your instruments then you need to take action. If your correction is for distance viewing the need will vary with severity. The nature of your mask in the water will provide some magnification. If your need extends beyond this natural correction then the right lenses will have you end your dive feeling more relaxed. There will be times that you surface and will want prime vision to sight landmarks, boats or buddies so don't sell yourself short here.
Contact lenses can be worn. If you open your eyes underwater it is possible loose a lens. Divers with contacts will squint in a mask off situation to keep them captured. If you are looking at a mono-vision contact lens configuration be sure that the left side is corrected for near vision, this is where your instruments will be. Lastly if you do expose your lenses to open water be sure to take the proper cleaning precautions to avoid an infection.
Some masks are made to accept their own prescription lenses. For a simple single focal prescription the dive shop can install the needed lenses. This is a nice easy solution. If your prescription includes "cylinder" correction of 1 or more then you will be best served by custom overlays that take this into account. Cylinder correction is usually for astigmatism.
For more complex prescriptions your local dive shop can send your mask and prescription to optical shop that bonds overlays to the inside of nearly any mask. The cost is comparable to street wear lenses and your mask is a relatively cheap frame. A quick Google search will uncover mail order providers that you can deal with directly should you choose. If you happen to have one of those Flex Spending prepaid medical accounts at work this is a great way to buy your dive mask with pre-tax dollars! Check with your administrator but I have not seen it denied yet.
There are plastic cling-on overlays that can be added to the bottom of your mask to help in reading your instruments. The do work optically and if installed properly are not likely to get washed away. I don't consider these a top shelf solution but they are an option.
For color correction you can get tinted lenses, generally red to help restore some of the natural colors lost with depth. If you have interest be sure you get a mask that will accept with or comes with these lenses.
