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Porro-prism binoculars - internal focussing

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#1 Guest_**DONOTDELETE**_*

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Posted 29 May 2004 - 09:42 AM

I've noticed that my Leica scope has porro prisms and achieves focus by moving one of the prisms. The advantage of course is that the volume of the scope remains fixed and thus the scope can be sealed against water ingress. I wonder why this mechanism has never been applied to binoculars? After all, one of the reasons many birders avoid porro prism binoculars is the lack of sealing.

#2 Guest_**DONOTDELETE**_*

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Posted 29 May 2004 - 12:15 PM

I've got Swarovski SL 8x56 porro prism with internal focus and water proof. Great binoculars the SL series too bad Swarovski discountinued these in favor of roofies.

#3 Guest_**DONOTDELETE**_*

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Posted 29 May 2004 - 02:52 PM

LustyLobster: I'd not heard of that binocular before. What sort of FOV does the 8x56 have? Any idea how it achieves the internal focus?

#4 Guest_**DONOTDELETE**_*

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Posted 29 May 2004 - 03:04 PM

The field of view is 305' @ 1000'. They were discountinued about 6 years ago? Here's a link with info, they turn up on the bay now and then in 7x42, 7x50, 8x56 and 10x50. The eye pieces move internally from what I can tell.
http://www.birdware....lars/swarsl.htm

#5 Fiske

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Posted 01 June 2004 - 03:00 PM

My guess would be that internally focusing porros would weigh a lot more. My internally focusing Nikon LX 8x42 roofs weigh 34.6 ounces versus about 25 ounces for the Nikon 10x42 SEs.

Internal focusing is very nice -- for one thing, changing the focus does not rotate the eyecups (and cause the right diopter control to defocus(!) during use). Of course, the LXs also have a positive diopter lock. Another nice feature.


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