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Do some brands advertise area magnification instead of linea

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Do some brands advertise area magnification instead of linea

Postby Guest on Wed Jun 26, 2013 4:29 pm

I recently bought a $15 pair of GSI 10x50 binos online somewhere else, free shipping. I was very upset to discover they only had a linear magnification of 3x, not 10x, even though 10x50 was printed on the binos themselves. The square root of 10 is about 3, so maybe they meant area magnification, not linear magnification. And since the apparent field of view was 1/3 of my normal eye sight, meaning a small circle and lots of black around it, the specs were accurate about the 6.5 degree viewing angle.

I went to Big 5 to try out some other brands, including a $99 Barska 10x42 and a $65 Bushnell 10-30x50. To my frustration, both only had a 3x linear magnification. At 30x, I was able to hold them steady as I looked at the sign at the back of the store. The sign was linearly magnified about 5 or 6x.

Are there any 10x50 binos that actually give a 10x linear magnification, or does 10x always mean area magnification?

I went over to an astronomy gift store on campus and asked if they had binoculars. They only had kid ones, but I had a look. The 4x ones made the chairs across the room look twice as tall. The square root of 4 is 2. I asked the astronomer about this, and he said magnification is supposed to refer to linear, and that maybe I'm not viewing things right. I think he is just used to expensive optics that don't false advertise.

Is it possible for me to get a true 10x linear magnification for under $50, and a field of view that does not look like I'm looking through a paper towel roll?

Thank you.

Re: Do some brands advertise area magnification instead of l

Postby Steven_L on Thu Jun 27, 2013 12:32 pm

10x binoculars make things look 10x closer. You are overthinking everything. FOV has to do with the eyepiece construction, no math involved. 10x binoculars are 10x what the eye sees, and 50mm is the objective size of the lens in MM.
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