I take my glasses off. Focus the diopter on the 'on screen data' and shoot. Been doing it that way for years. Always looks ok on a monitor with my glasses back on.

As Owen said, another target to check for focus in the viewfinder is the data displays in the viewfinder.

If you can get these to look sharp, by adjusting the diopter in the PD170, then you can be assured that if the image in the viewfinder looks sharp, then everything else will be, too.

By the way, I'm also facing the issue of presbyopia: where the crystal lens in the eye becomes progressively stiffer and unable to "accomodate" or adjust to different distances. Seeing things up close or at distance wasn't a problem until I started passing 45. Reading glasses made it easier. Now reading glasses are essential and it makes shooting more difficult.

I'm fortunate to have a step daughter who recently became an optometrist. Unfortunately, she's 3,000 miles away! But at least she can tell us about the latest in technology.

And the latest isn't Lasik, but a lens implant that simulates the adaptability of a normal eye.

My daughter told me that in people over 50, they now look at the possibility of doing a CrystalLens implant instead of Lasik. By that age there's a potential for cataract development and, rather than subject the patient to two surgeries, just do one.

This implant allows for near-normal accomodation. People who have had these implants can see far, of course, but they can also see close. It's not perfect -- you can't spend hours reading a novel -- but it eliminates the need to use reading glasses for routine situations.

Sounds rather bionic, doesn't it?!

Heck, we're in the 21st Century...!