Q:

Wearing under corrected diopter diving mask (hyperopia)

I have hyperoptia with roughly +5 diopters on both eyes and considering occasionally using diving mask for snorkeling in summer.  The problem is, these masks usually come only up to +3.5 diopters and prescription mask is too high investment for few days a year.  
I'd like to ask, if using +3.5 diopter in my case would improve situation from just using normal mask – I can see well enough without glasses for limited time, but it is not comfortable for my eyes. 

A:

Since nobody answered, I tested it and it does help.  If you have hyperopia with +5 diopter and use lenses with diopter +3.5, it effectively lowers your eye diopter error to +1.5 (with some difference due to water refraction index, depending on where the lens is).  
In practical terms, with +1.5 diopter you will see things very close to you somewhat blurry, but other things reasonably sharp, so it can be good enough for snorkeling. 
If you are in doubt, use for example this application:
http://www.mediawebtool.com/tablet/optos_vs/diseases/hyperopia/
Take diopter error of your eye, subtract the diopter of the lens you want to use and you will get error of your eye after correction.  See, if it is good enough for you.