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Started by Thomas Marshall, 04/06/2016 05:41AM
Posted 04/06/2016 05:41AM Opening Post
I bought "as is" used bino's on e-bay/PayPal. Labeled 30X50 and touted as "High Power" bino's. Now I am in quarrel with seller who is complicating the "return" of item. Bad collimation that I adjusted 90% better, but gave up finishing the tweaking of them when I realized they are not actually 30X, but rather show exact FOV and image size as my 7X50 bino's and no amount of tweaking could fix that. He wants me to pay return shipping and hold refund till a camera shop verifies they are not 30X50 as labled. How do you calculate exact power of bino's?? I have the 50mm part, but eyepieces are not labeled like telescope eyepieces, - 12mm/25mm etc. I told him the difference between 7X bino's and 30X bino's is the difference between Saturn looking like a star and looking like the ringed planet it really is. No possible way bino's that are supposed to be over 4 X the power of 7X50's could have exact FOV and image size -- Right?? Thomas M. :S
Posted 04/06/2016 11:43AM | Edited 04/06/2016 11:50AM #1
Yes, there are many easy ways; try this one: Grab a clear mm ruler. Aim the binos down at a bright floor and see that bright circle of light behind one eyepiece. Measure its diameter "D." Your mag is 50/D. If the binos are 7x50s, that circle will be 7mm. If they are 30x50s, it will be 1.7mm. I just grabbed my 7x42 binos here and did that. I measure 6mm. 42/6 = 7. This method never fails. The Russians actually make a "pupil scale" instrument that measures that very accurately! Tom

29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos