CanonLearner wrote in post #15496447
That's not the problem. The problem is that the diopter wheel says ''very very far to the left'' when in reality it's at neutral adjustment. I have very good eyesight and the wheel is very far left to get a crisp image. Just one more click and it'll be off the scale of far left setting, so I worry about it going off the scale and not being able to get a sharp viewfinder. I'll edit my original post to make this clearer.
The only way you will exceed the range provided by the built-in viewfinder diopter adjustment, i.e. "go off the scale", is if your eyesight actually isn't as good as you think it is, or if the camera has deeper issues. On the 5DII, the diopter adjustment provides a range from -3 to +1, which is more than enough for a lot of fine tuning adjustment to individual eyesight. Probably will accomodate 95% of people or more. I wear eyeglasses and shoot with them on. On all my Canon I have to adjsut the diopter slightly, but have never even bothered checking how close it is to one end of the range or the other (because it really doesn't matter, I'll be getting a new eyeglass prescription if and when the range of adjustment is inadequate).
You are misunderstanding the way the diopter adjustement works. There is no way simply by bumping and moving the wheel accidentally that it can get "out of whack" to the point that it can't very easily be adjusted back. When you readjust it for your personal setting it should always return to the same point, if you have it adjusted correctly and nothing else has changed. If "one click from the farthest possible left position" is correct for you, that is your personal "neutral" setting, and it will always be correct for you unless or until your eyesight changes. Someone else using the camera will likely have a different "neutral" setting. It's also likely very few people will adjust and use the diopter set exactly in the middle of the range (equal clicks to both extremes, or what you are refering to as "neutral"). Most will need it set a little one way or another. So long as you are able to achieve a setting where the focus screen markings are nice and sharp, you have nothing to worry about.
If at some point in the future your near eyesight deteriorates beyond the range provided by the built in diopter, you can simply add an accessory diopter to increase the available range of adjustment.
The only way you can exceed the range provided is if your near vision eyesight is worse than you think, or if the camera takes a really hard bump and the focus screen is misaligned or something in the pentaprism is seriously out of whack (in which case repairs are called for). As solidly as the camera is built, those are very unlikely, but you might check that the frame holding the focus screen in place is properly latched closed (see your user manual for more info).
P.S. It occurs to me that if you wear and shoot through eyeglasses that are bi-focal or tri-focal, the diopter adjustment needed might differ or even be more extreme, depending upon what portion of your eyeglasses you are looking through when you shoot. Just a thought. Might need to wear single strength eyeglasses when shooting, if this is a problem.