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Message: <blockquote data-quote="henry link" data-source="post: 3274999" data-attributes="member: 6806">Not sure about "Trilar", but "RLE 76.4" refers to the concept of "Relative Light Efficiency". That was an effort in the first decades of coated binoculars to vaguely quantify the improvement of coated binoculars over uncoated binoculars. Basically you square the exit pupil diameter and then add 50%, so a binocular with a 5mm exit pupil and fully coated with single layer AR coatings was said to have an RLE of 37.5. Using the same math a 7x50 has an RLE of 76.4. I have some old Swift material from the 80s, which assigns an RLE of 76.4 to the cheaper single layer coated 7x50s in their catalogue and an RLE of 84.2 to the more expensive multi-coated models.Henry</blockquote>