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Message: <blockquote data-quote="DanLegere" data-source="post: 3187207" data-attributes="member: 131484">I was reading this old thread: <a href="http://www.birdforum.net/showthread.php?t=146768" target="_blank">http://www.birdforum.net/showthread.php?t=146768</a>And <a href="http://www.birdforum.net/showthread.php?t=260248" target="_blank">http://www.birdforum.net/showthread.php?t=260248</a>I have been trying to figure out how to use the formula but dont think I'm doing it right. I put my binoculars on a tripod, with the eyepiece facing a wall. I measured 25" to the wall from the eyepiece glass. I then put a light through the objective, and got a 27.5" wide circle on the wall. Could you explain how would I enter Johns forumla in my calculator? My binoculars (Bushnell legacy 10x50 6.5') should be close to 65' AFOV.<img src="http://s25.postimg.org/m2i0796rj/150317_1915_2ee.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />I have also done another method, where you face the objectives to the wall, and look through one eyepiece, while looking at the wall with your other eye. You then mark on the wall where you see the edges of the field stop, and note the distance between them, and the distance from the wall to the eyepiece. In my case, it would be 25"D to the wall, and 30.5"W between the points on the wall.The formula for this is AFOV = 2*Atan(W/2/D)= 62.7'<img src="http://s25.postimg.org/hs3cbo1of/150317_1859e.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />But what I'd like to know is how to use the the formula for the light projection method.</blockquote>

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