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Barlow Question

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#1 oldtimer

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Posted 22 September 2021 - 10:53 AM

Best way to ask my question is to give example. I have a 200mm F4 (800mm) reflector and a 9mm 100 degree eyepiece, so the math says 89X 1.12 degree FOV.  Now I add a 2x barlow. The math says 44.4X with a 2.25 degree FOV.  Am I missing anything?

 

Gary (olltimer)



#2 NorthernlatAK

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Posted 22 September 2021 - 11:34 AM

That's incorrect. The magnification will be doubled while fov gets halved. The 2× Barlow doubles your effective focal length, therefore doubling the magnification.
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#3 oldtimer

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Posted 22 September 2021 - 12:05 PM

Thanks! How did I get this  this backwards?.Must be old age!


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