Regarding your initial question I cannot prove from real live, but e.g. the SKU # 32214 45° viewfinder is able to compensate -3 to +3 dioptries, so it should work with a mask with +2 or +3 glasses (https://drive.google.com/file/d/1ZXdgS9N8TIgeciMzXb9GHhORUeA-pL-b/view)...
Having a permanent reading glass of +2 or +3 dioptries in the mask may be a cheap solution, but it is probably not comfortable considering that visual perception is the most important perception while scubadiving and also while taking photos UW...
I personally prefer to have all my optical ametropias corrected by having glued-in and multifocal lenses in my mask, fabricated by a dedicated company. Vision is similarily perfect as with the glasses that I wear above the surface (nearsightedness, astigmatism and presbyopia). One could even think about including extra + dioptries at the near end, to get some magnifying glass effect, but i did not dry this...
Since I have such a mask, I just can forget about all my optical problems. I can read again finnimeter and diving computer easily. My 45° viewfinder is no problem with this mask. This comes at the cost of about 700 Euros for such a mask, but I think it was a very worthy investment. I have other, more expensive, items in my gear list that I could omit more easily...
Wolfgang
Very easy to feel at home here: not only similar, put improved, format as Wetpixel. Chris and Tim from the old moderator team and Davide as a new moderator - Just stay on the ball! Wolfgang
