I can't even begin to tell you how many times I've photographed families at weddings only to have it look like 'Dad' is wearing sunglasses because he's wearing transitions lenses!  This is a HUGE problem especially for outdoor weddings.  As a photographer it's tricky because I have two choices...have them look like Ray Charles or ask them to take off their glasses which often times they wear ALL the time so they don't look like themselves in the photos.  If it's someone who is really close to you and will be in a ton of pictures (groom or Dad) simply ask them ahead of time if they could bring/get another pair of glasses that aren't transitions lenses, or if they have an old pair they don't use that you could pop out the lenses on for the important photos.