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Low Mag / High Mag
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12-09-2017, 02:40 PM
Merlin66
(Ken)
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Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,907
Col,
If it's 100mm f5 then the focal length is 500mm.
To get x20 the eyepiece fl needs to be 1/20 of 500 = 25mm
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