Most of the replies seem to be near sighted aging photographers. Thats me as well. I understand the difficulty of viewing the upper corners of the GG if you are using the bottom edge of your bifocals - I can feel the neck strain thinking about it. If you are indeed near sighted, for some people the simple solution is taking their glasses off. If you are far sighted, that is not an option whatsoever, and the flip down magnifiers might be in order. Saint Ansel wore those. Strong astigmatism can only be corrected by eye glasses in general, and if this is a factor, again flip down magnifiers could well work.
Personally, I have been corrected for myopia since my early teens with glasses. For the past 30 years however, I switched to contact lenses, because I hate bruised ears and noses. I am assuming you don't mind wearing glasses. But with my contacts to correct for far vision, to correct for aging (presbyopia) I simply use 1.75 or 2.00 reading glasses for daily tasks and I will wear a pair of 3.00 reading glasses at the ground glass. Reading glasses have the advantage of covering a large area, so I can view the ENTIRE ground glass for composition, not just view a small area for focus.
One last option I would suggest if you want to continue with the bifocal route is to get regular bifocals not progressives. It will give you a much larger truly correct viewing angle. Also, you might discuss with your optometrist - optician the dividing line for the magnifying portion, if he/she understands your need to tilt your head severly when you are under the dark cloth, you might get a much better solution. And remember that you might consider two solutions. One for daily tasks, and a separate one specifically for photography.
