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JanS
professor emeritus
Reged: 12/24/05
Posts: 566
Loc: K/W
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This is probably a newbie question, but is there a correlation between an eyepiece's afov & how well it works in a binoviewer? I guess what I'm asking is if one used superwide eps, say with 82deg afov, would the bino effect be improved over eps with narrower afovs? Or does the fov or afov even matter?  Thanks! 
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GOTO #106 75mm f17
Meade 10" LX200GPS EMC w/UHTC
TeleVue BinoVue
(2) 24mm Panoptics
A whack of Meade Super Plossls
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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 630
Loc: Ottawa, Ontario, Canada
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It depends on the combination of the rear aperture of the prisms in the binoviewer and the eyepiece field stop diameter. Moreover, the distance between prism aperture and field stop (or built-in "Barlow-like" lens in many ultra wide eyepieces) can be of some importance, too.
Cheaper binoviewers have ~20mm apertures, while the Denkmeiers have 26mm. And I guess Seibert units are coming down the pike with even larger clear apertures still.
An eyepiece with a field stop much larger in diameter than the prism will suffer vignetting at the edge of the field. If not too bad, vignetting will appear as a not-too-objectionable greying-out, confined to the very edge of the field only. Severe vignetting will actually reduce the available field of view somewhat.
An off-the-cuff rule of thumb (which can stand modification by those who regularly *use* binoviewers):
With wide angle eyepieces in the 65-70 deg. afov range, the longest useable focal length is about equal to the prism aperture. Ultra wide maximum focal lengths might be limited to 3/4 (?) of the prism aperture. But the behavior of the "Barlow" just *might* allow a focal length approaching 90% (?) of the prism aperture.
I hope someone chimes in with some real life data.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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David E
Carpal Tunnel
Reged: 05/25/06
Posts: 1759
Loc: North Carolina
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Quote:
This is probably a newbie question, but is there a correlation between an eyepiece's afov & how well it works in a binoviewer? I guess what I'm asking is if one used superwide eps, say with 82deg afov, would the bino effect be improved over eps with narrower afovs? Or does the fov or afov even matter? Thanks!
Here's by basic rule about eyepieces and binoviewers: if you like the eyepice and it's comfortable to use, it's a good candidate for a binoviewer pair. A lot of people don't like low power wide field eyepieces because with binoviewers they rarely look at the extreme edge so this tends to be "wasted" field of view (i.e. wasted money). I am in this camp myself. However, when it comes to higher powers (shorter focal length eyepieces) I do like the ultra wide field of view. I have a pair of Meade 5000 series 6.7 UWA's that for me work great as a bino-pair. The 82º field of view becomes an asset at this power.
David E
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David E
So when at times the mob is swayed
To carry praise or blame too far,
We may choose something like a star
To stay our minds on and be staid.
-Robert Frost
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JanS
professor emeritus
Reged: 12/24/05
Posts: 566
Loc: K/W
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Quote:
Here's by basic rule about eyepieces and binoviewers: if you like the eyepice and it's comfortable to use, it's a good candidate for a binoviewer pair. A lot of people don't like low power wide field eyepieces because with binoviewers they rarely look at the extreme edge so this tends to be "wasted" field of view (i.e. wasted money). I am in this camp myself. However, when it comes to higher powers (shorter focal length eyepieces) I do like the ultra wide field of view. I have a pair of Meade 5000 series 6.7 UWA's that for me work great as a bino-pair. The 82º field of view becomes an asset at this power.
David E
That's sounds viable, and your choice of eps is interesting, it was the 5000 series 14s I was thinking about. That said, I guess I need to see if I can find someone locally and at least try one out. Thanks for the advise 
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GOTO #106 75mm f17
Meade 10" LX200GPS EMC w/UHTC
TeleVue BinoVue
(2) 24mm Panoptics
A whack of Meade Super Plossls
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