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Focal Length of Nikon 80mm Sky and Earth? (1 Viewer)

william j clive

Well-known member
Does anyone know the focal length of the 80mm Nikon Sky and Earth spotting scope? Alternatively the focal length of the 33x Wide Angle eyepiece for this scope would help. Thanks in advance. Henry, are you there?

henry link

Well-known member
I'm here, but I don't know the answer. If Nikon is unable or unwilling to tell you there is a way to find the focal length of the scope by measuring the field stop diameter of the eyepiece. The field stop will probably be visible from the front end of the eyepiece. It should look like a narrow metal ring just in front of the first glass element and a bit smaller than the inside diameter of the eyepiece tube. Measure it's diameter in mm's as accurately as possible and multiply that number by 57.3. Divide that number by the scope's real field in degrees when the 33X eyepiece is used on it. The result will be the scope's focal length in mm's.


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