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Message: <blockquote data-quote="typo" data-source="post: 3534283" data-attributes="member: 83808">CJ,I just checked the actual distance between the rim of the eyecup at the setting I normally use with my glasses and the ER convergence point for my three most used binoculars. They were between 11 and 12mm. They vary quite a bit in eyecup shape and diameter but the answer comes out about the same. 10mm is about my lowest limit and more than 14mm I need to twist out the eyecups. The information I would like from the companies is whether there is over 10mm ER available. For others with different frame designs and/or prescriptions that figure might be 15mm or more. If available ER was accurately listed we would all very quickly learn what works for us. Listing a true ER of 15mm for three different binoculars is useless to me if one is just right, another needs the eyecup twisted out one click and the last is totally unusable.Without glasses, I suspect the distance between the fully extended eyecup and the convergence point would be equally useful. That simply means the range of available ER is probably the best starting point. Obviously, other information like eyecup diameter would be helpful in understanding how a particular model would work for you. All three of those binoculars I own give me blackouts at full eyecup extention without glasses, but how would you know if they would for you?Those three binoculars had 14.5, 15.5, 17.5mm ER available at their lowest eye cup setting, and had roughly 4, 3, and 2.5mm between the level of the rim and the centre of the lens. That should make the real ER values 18.5, 18.5mm and 19mm respectively. The company websites show them as 20, 19.5 and 19mm. There will be a margin of error on my measurements but it rather looks like two ERs might be slightly overestimated, but interestingly, and the one with the least listed actually had most available. It's the one I lend to visitors who wear thick rimmed, strong prescription glasses.Obviously I have no idea of the discussions that went on in the ISO meetings. I can't think of any optical reason for a need to have such a wide range in the specification. I believe many of the major companies are represented and no doubt looking after their own interests and most likely would want to ensure they didn't need to rewrite their brochures. In theory at least, that +5 to -0.5mm range should limit exageration, but in practice it would also allow those who wish to list available ER instead of true ER to be compliant. We just have little idea who they are. At the moment it's a total lottery for those who need a bit more ER.As for going round Birdfair trying different models. I sometimes make a mental note that the available ER on a particlar model is generous and might need the eyecups twisted out a click or more, but you would need to know both my and your own available ER requirements to make much use of that. You know mine now. Maybe by next BirdFair you will know yours as well. Unfortunately I've changed my glasses so don't rely on my previous comments, and what happens if I change them again? Wouldn't life be easier if they just told us the available ER range?David</blockquote>

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