BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="typo" data-source="post: 3399708" data-attributes="member: 83808">It's true a resolution test only determines the ability to resolve, that is, separate close objects and is one measure of the optical accuracy. It's the same process the optician uses to test your eyesight using a letter chart, but you get the sme answer if you used lines, stars, Landolt C, Tumbling E or any of the more sophisticated analytical tools like MTF or inteferometry. If the opthalmologist tells you that you have 20/20 vision then it means that a specific light level (and sometimes contrast level) your eyes can distinguish features down to an angle of 120 arceconds. If it's 20/10 then it's 60 arcseconds. It's not the only test they do, and eye hospitals can do a whole lot more, but it's the one that really tells you how good your eyes are working. Size of letter and distance translates to an angle of view which is a limit for your eyesight.You would hope that an 8x binocular will allow to see the limiting detail at 8 times greater distance. It cannot do better than that, but it can be worse. So for those with 20/20 vision the angle will be 120/8 = 15 arcseconds and for those with 20/10 it will 7.5". Providing the effective resolution of a binocular is better than those numbers, your eyes will limit the detail you see. A very simple comparison. Do a regular eye test with any kind of chart, and the with a binocular on a tripod, compare the result at 8 times the distance. There is a complication, if the light levels change between reading the results won't match, but otherwise with good binoculars it works every time. If the binocular effective resolution is worse than your magnified acuity, it won't. For that individual that's a bad binocular. Simple! Unfortunately your eyesight is going to be different to mine so your result or is worthless to me (and hand held just makes it a total nonsense). Why would I have the remotest interest in the result (or opinion) of someone with 20/20 vision if I had 20/10 eyesight? I would need a binocular to be twice as good. Someone with 20/10 eyesight would need a binocular to have an effective resolution better than 7.5 arcseconds not to be limiting but anything better than 15 arcseconds would be fine for 20/20.I've tested quite a few binoculars now for effective resolution. The diffraction limit means that the best resolution possible for an optically perfect lens is around 5.8 arcseconds (20mm). The good news is that many are better than 7.5 arcsecond, though my results range from 5.84 to 14.5 arcseconds. At least if I report a value better than 7.5 arcseconds you can be sure that for everyone any limit to the detail you can see will be down to eyesight.We have yet to see Henry's effective resolution (20mm stopped down) results are for the Habicht, EII and SE. The last x32 I tested was a fairly cheap Hawke Frontier ED. The full aperture resolution was 5.8" which looks pretty abysmal compared to Henry's results of 4.75" or better. However the effective resolution of 6.8" which should keep everyone happy. For comparison, Tobias Mennie told me the best he got in his mega-shootout with the alphas was 6.6".I've already said that there are many aspects that contribute to the quality of the view so perceptions are likely to differ according to who, where and when the comparison was made. I've only compared the Habicht and EII briefly on a hot sunny day. I could see absolutely no difference in detail as I would expect for binoculars of this quality (and my eyesight is very good). However the glare made the view through the Habicht look rather washed out and the contrast suffered. The EII looked perceptually sharper under those conditions. A different time and place and I quite accept the results might be reversed. But the effective resolution won't change.David</blockquote>

Verification