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Falcon Birder
super member
Reged: 04/16/07
Posts: 111
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Quote:
Because their barrels are closer together , roof prism do tend to have closer focussing than Porros , which can be a HUGE advantage for birders ,Regards , Kenny
Kenny, I am trying to understand the above statement. Why the distance between two barrels will determine the close focus of binoculars? Thanks
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Zen-Ray SUMMIT 10x42 WP
Swaroski 8.5x42 EL
Leica 8x32 Ultravid
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
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Parallax. Objective lenses are always wider appart in porros, therefore porros experience greater parallax at closer distances. This makes it more difficult to overlap the field of view in the two objectives.
Take note of the extreme close focus Pentax Papilio. This binocular focuses by moving the objective lens. As the binocular focus is turned more towards extreme close focus it is accomodated by also moving the objective lenses closer to each other. What this means really is that the optical paths of the two sides are actually NOT parallel, but very slightly turned inwards so they converge to form one perfectly overlapped image at very close distance.
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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Falcon Birder
super member
Reged: 04/16/07
Posts: 111
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I see. Thank you!
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Zen-Ray SUMMIT 10x42 WP
Swaroski 8.5x42 EL
Leica 8x32 Ultravid
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KennyJ
Reged: 04/27/03
Posts: 10146
Loc: Lancashire UK
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EdZ ,
Thanks for answering that question on my behalf , so accurately and concisely .
MY version would probably have rivalled War and Peace for verbosity ! :-)
Kenny
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If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Just one picky comment. I agree with Ed about the objectives being wider on STANDARD porro prism binoculars. There are small porro prism binoculars that have their objectives very close together. I belive that the design is called a reverse porro, but I may be mistaken.
The Papilios are an example of such a reverse porro design.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
Edited by pcad (10/27/07 04:02 PM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
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The Papilios is a good example of this reverse porro design. Typical seen as objects closer together than eyepieces.
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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