AlanFrench
Well-known member
I had a chance to do a little informal experiment today. I had my annual eye exam, and arrived home with my pupil still dilated to about 8mm.
I like my 7x42 binoculars because they "snap" into focus, and the correct focus is quite obvious. What would happen when my pupil was open wide enough to accept the entire 6mm exit pupil? I found that the no longer snapped into focus and there didn't seem to be a really correct focus. I'd get to a point where they looked almost there, and further motion of the focus knob in that dirrection would just make it worse.
For comparison, I tried my 12x36s. With the smaller 3mm exit pupil serving to stop down my eye's pupil, the correct focus was obvious, although they didn't seem quite as sharp as during normal use. It may well be that I didn't quite have their exit pupil lined up with the center of my pupil where the eye's image quality is best.
Alan
I like my 7x42 binoculars because they "snap" into focus, and the correct focus is quite obvious. What would happen when my pupil was open wide enough to accept the entire 6mm exit pupil? I found that the no longer snapped into focus and there didn't seem to be a really correct focus. I'd get to a point where they looked almost there, and further motion of the focus knob in that dirrection would just make it worse.
For comparison, I tried my 12x36s. With the smaller 3mm exit pupil serving to stop down my eye's pupil, the correct focus was obvious, although they didn't seem quite as sharp as during normal use. It may well be that I didn't quite have their exit pupil lined up with the center of my pupil where the eye's image quality is best.
Alan