Cameras and Lenses
General Technical Question
Hi everybody
My eyeglass prescription is -4.75 left eye and -4.25 right eye. When using my binoculars should I have the dioptre adjustment dead centre? In other words, is my eyesight already corrected for viewing through the bins, or does the relative weakness of my left eye need further compensation?
I find that generally the bins work best at the centre setting, but sometimes a little tweaking either way makes things slightly sharper. I guess it holds true for all binoculars, but mine are Leica Ultravid 8x32 (earlier non-HD version).
I'd be grateful for any wisdom out there!
Cheers
John 
Hi John;
Your prescription should correct your eyes to zero diopters, infinity. There should be 0d difference with your glasses on. Without your glasses the Leica may focus about 60-65 degrees further clockwise and may run out of adjustment before reaching infinity. In this situation, you would adjust for the difference.
An uncertainty of a quarter diopter is pretty common plus the diopter adjustment on the binos may be a little off.
Best
My eyes are about the same, except my right is the weaker at about -4.75.
If wearing the glasses when viewing then the glasses take care of the diopter difference. So the bincoulars should be set with the adjustable one at 0.
Most of the modern binoculars are fine for use with glasses on having usually wind up/down eyecups to adjust for the eye relief.
If you don't use the glasses when viewing then the adjustable one needs altering so that it compensates. Half a diopter should be easily within the adjustment. Usually they support +/- 1 diopter or 1.5.