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Mike,
Being "blind as bat" doesn't mean you can't observe without eyeglasses. Myopia is nearsightedness and hyperopia is farsightedness. These two issues on their own can be easily adjusted by adjusting the focus position with the focuser. Someone who is "blind as a bat" due to myopia (most common)without astigmatism can observe without glasses easily, I did it for countless years. The focuser travel itself provides the diopter adjustment that you normally get with your eyeglasses. In very simple terms, as you get older people with myopia usually also develop "astigmatism which causes the image to "rotate" slightly as well as focusing back from the retina (myopia). The eye's astigmatism cannot be corrected with the focuser. The effect of eye astigmatism worsens as the exit pupil gets larger because the astigmatism in the eye worsens off-axis. I have no issues observing with eyepieces of focal length less than 10mm in my F5 scope which creates a 2mm exit pupil in my scope. For eyepieces of FL longer than 10mm or exit pupil > 2mm, I need to wear glasses to observe. Off axis images that appear as point sources to everyone else when focused, appear as "slits" or "distorted triangles with tails", a bit like baby comets to someone with eye astigmatism, hence the need for "glasses on" when observing.
CS-John B
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