Hi All,
I've recently found that I need glasses for astigmatism and am curious how much eye relief is usually needed. I tried my binoculars (supposed to be 18mm eye relief) with my sun glasses and I could not see the full FOV. I'm thinking the sun glasses must have something to do with it and when I purchase glasses I'll get ones that sit closer to my eye.
But on average how much eye relief is needed?
Thanks for any imput.
Nick
[QUOTE=Nickolas]Hi All,
I've recently found that I need glasses for astigmatism and am curious how much eye relief is usually needed. I tried my binoculars (supposed to be 18mm eye relief) with my sun glasses and I could not see the full FOV. I'm thinking the sun glasses must have something to do with it and when I purchase glasses I'll get ones that sit closer to my eye.
But on average how much eye relief is needed?
Thanks for any imput.
Nick[/QUOTE]
Nick,
I have often seen 15mm quoted as "adequate for eyeglass wearers." As you have found, that number can be a bit optimistic. I previously had larger glass that sat farther from my face, and they required about 19mm of eye relief. I now have a smaller pair that sits closer to my face, and I can get away with 15mm. If I add my clip-on sunglasses, however, I can not see the entire field with 15mm of eye relief.
To complicate matters, manufacturers don't seem extremely consistant in how they measure eye relief. If it is from the eye lens, and the lens is rather recessed because of the design, the number can be misleading.
I think the only way to figure out if a particular pair works for you is to try them. It sounds like you might want to start with those claiming about 20mm of eye relief. With good, adjustable eye cups, it is easy to adjust them if you actually need less. If you have too little, you are stuck with a restricted field or with taking your glasses off.
Clear skies, Alan
The amount of eye relief that you will need depends on how closely your glasses fit to your eyes AND how closely your bino oculars fit to your glasses. In general, binos with smaller diameter oculars do not need as much eye relief as those with larger oculars (because they fit more closely against the glasses). For myself, I have binos with as little as 13 mm eye relief through which I can see the whole field, and others that supposedly have 17 mm that do not have enough. I prefer 16-20 mm. Some of the variation has to do with how different manufacturers measure eye-relief, but much has to do with this issue of fit to my glasses.
Until you have figured out what combinations of factors work for you, the advice to try before you buy is solid. Incidentally, make sure you test for adequate eye relief under conditions of BRIGHT LIGHTING! It seems that when you are pushing the limits of a binos' eye-relief, the view is more constricted when one's pupil is contracted.
--AP