M. Currie
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 p.1 #11 · Does the vision impediment affect the manual focusing? | |
My problem is a little different, and not as bad in the end, but here's my story:
A few years ago I had a bad bicycle accident, causing brain stem injury, including the trochlear nerve which controls the way one's eyeballs adjust to the horizon. Since then, my two eyes have differing horizons, which cannot be corrected, and I see double up close. My left eye tilts about 5 degrees down toward center, and the right about 5 toward center, maybe a tiny bit less.
To visualize this, imagine looking at two transparencies overlaid of the same thing, each tilted slightly. The one closest to you is normally the dominant one, I think. Currently I see those two transparencies, and the right one appears vertical, even though the left is in front of it and always provides a ghost image. One gets used to it, and the brain can put the images together at the top, and at distance, so I have binocular vision to drive, but must squint to walk down stairs or read.
The interesting thing here is that, for the previous many years, my vision had been left-dominant, and I always used the left eye for photography, even though it's visually a little weaker. The right is more far sighted. Overnight, I found I had become right eye dominant. My brain had to compensate for the skewed horizons and decide which eye would determine the level of the world, and chose the right. If I close my right eye, the world appears to be about 10 degrees tilted. So I also simply began using my right eye for photography as well. It took a little while to get used to this after over 40 years of left-eye viewfinding, but that's what worked best.
For normal horizontal view, I get straight horizons, but vertical needs the built in level. Live view is always tilted without a grid overlay. For critical vertical shots I tend to shoot a little wide so I can fix it in post.
I don't know how other brands work, but for the Nikon I use, a correctly calibrated lens will light the focus confirmation dot even in MF, so I can usually get a pretty good focus even in MF by watching for the dot. Practice helps too, and so does viewfinder magnification if you can find something for that.
Which is the long-form version of the advice that, if one eye works better for viewing, I'd just start trying to get used to it. Set the diopter, and work on improving your focusing ability with that one. If you're using a tripod for macros, try live view too.
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