EdZ
Professor EdZ
Reged: 02/15/02
Posts: 18806
Loc: Cumberland, R I , USA42N71.4W
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I have the 6.5x21.
By measuring superimposed area on a scale.
At 20 feet they are a bit more than 6.5x
At 6 feet they are about 7x
At 2 feet they are about 8x.
By measuring exit pupil, I get 3.2mm, 2.9mm and 2.6mm. These exit pupils correspond to 6.6x, 7.2x and 8.1x, very close to the scaled images.
Of course, they do this because when you focus, the objective lens moves, a lot.
At 50 feet they measured near exact 6.5x
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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edwincjones
Close Enough
Reged: 04/10/04
Posts: 7980
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thanks edz,
now I can tell people that I have the 6.5-8x21 papillios
zoom binoculars are getting better
edj 
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Amalia
Reged: 10/16/04
Posts: 5165
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I have read somewhere in the www that this
is a common change performed by porro binos.
I don't remember more, but if you want, I
could try to find it again.
Amalia
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 18806
Loc: Cumberland, R I , USA42N71.4W
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Actually we have a few threads in this forum about change in magnification in porros. Links would be found in the Best Of - Testing Aspects of Binoculars. Normally, when you focus binoculars the eyepieces move in for distance and out for close focus. The eyepieces might travel 5mm-7mm. This difference puts the eyepieces either closer to or further from the objective lens, by a small amount. But for a 50mm f/4 lens that can be a difference from 200mm to 207mm. With a 20mm eyepiece, you can see that has the effect of changing magnification from 10x to about 10.4x. Such is the case with almost all binoculars.
With the pentax papillio, the objective lens moves about 20-25mm.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (03/24/07 05:02 PM)
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