Your mask acts like your eyes in the water, creating a pocket of air in front of your eyes by creating a seal against your face using the mask skirting. The pressure of this air...
Your mask acts like your eyes in the water, creating a pocket of air in front of your eyes by creating a seal against your face using the mask skirting. The pressure of this air pocket increases as you descend through the water column (Boyles law for the geeks out there). You'll feel this pressure on your eyes and face, and can easily be counteracted by exhaling slightly through the nose, equalising your mask. Ideally, you want to minimise how much air you have to exhale into your mask in spearfishing and freediving so a lower volume mask makes sense.
Dual lens designs have 2 lenses, separated by the nose pocket. The biggest advantage of a dual-lens design is that they are able to be fitted with prescription lenses. Some divers also claim this design is easier to clear than a single lens, as they typically have a lower volume. For the same reason, you might assume that equalising is slightly easier.
Whether you prefer a dual-lens or single-lens mask is somewhat a matter of personal preference. Our philosophy at Adreno is that the best mask for you is the mask that fits best, so what type of lens you sport shouldn't be a huge concern.
Before using a new dive mask you will need to get rid of the factory seal used to protect the mask while it is on the shelf. A DIY method to prevent fogging is to rub some toothpaste into the lens of your spearfishing mask, leave for three minutes, wash off, and repeat this process three times. This helps to ensure you can see clearly on your first dive. There's nothing worse than not being able to see what you're doing because of a foggy mask.
The best method we've found is like the toothpaste method but instead using a specially formulated substance called Sea Buff - which is more effective than toothpaste.