Diopters
By Mike Pasini, EditorImaging Resource Newsletter
If you're among those with less than perfect vision, being able to frame your shot with an LCD instead of peeking through a tiny little viewfinder may seem like the brightest idea since baked bread (a much bigger deal than sliced).
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But there are times (dark ones) when you do have to peek through that little viewfinder to see what the lens is looking at. And when those times come, you may not be able to see the full frame if you have to put your glasses on to look through it.
To solve that annoying little problem, some viewfinders have a small thumb wheel nearby that lets you adjust the focus of the viewfinder itself. It's called a diopter adjustment.
Prepare yourself by looking at something within shooting range, raise the camera's viewfinder to your eye, and adjust the thumb wheel until the scene is sharp. That's all it takes to make a diopter adjustment for your vision.
Sounds easier than it is, however, because your eye is very accommodating. It will focus and refocus. Remember the goal is to be able to move the camera to your eye, after looking at your shot normally, without seeing a blur.
Where'd it get that ridiculous name? Diopter is simply the name of a unit of measurement for expressing the power of a lens (equal to the reciprocal of its focal length in meters, actually). A one-meter lens is half as strong as a half-meter lens. The half-meter lens has, we'd say, a refractive power of 2 diopters.
