Features needed in a mask (or goggles), are very similar whether primarily intended for snorkelling or
scuba diving.
A mask requires that you to go to a specialist shop and try various masks on. The 'does it stay on my
face' test is a must.
I like masks with side lenses (as well as the main front lens). Make looking 'around the corner'
for your buddy, or sharks, much easier.
Usually you are looking for fish to photograph but sometimes they find you.
This particularly applies to pelagic fish, sharks, stingrays etc.
The more warning or time the better the chance of that good lucky snorkelling photograph.
Whether the main front lens is a single or split type is your choice. Some find a split front lens
gives better access when pinching the nose to equalise ear pressure.
As a permanent wearer of glasses - a snorkelling mask that takes purpose-built prescription lenses is a
must. A job for an optician.
Don't buy prescription 'inserts'. They fog up as you now have three glass surfaces, the inside of
the mask and both sides of the inserts.
Remember, one eye needs close vision for the camera's LCD screen, which I usually hold at about arm's length.
The focus of the other lens/ eye needs more distance. Its easily done by an expert and costs for
sure, but not a fortune.
A new snorkelling mask will need its inner surface cleaning before use. Otherwise it will fog.
With finger, rub toothpaste over the inner side of the lens.
Leave overnight, rinse and repeat if still having problems.
Don't use a bleach or whitening toothpaste though!! Not good for some lens materials.
For regular cleaning of the mask lens, toothpaste is an option. Apply, finger rub lightly and rinse.
Easier and quicker to clean with baby's shampoo, (for babies, is milder so wont irritate your eyes).