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Prof M
member
Reged: 07/26/09
Posts: 49
Loc: Southwest Utah
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Why is it that many astro binos have individual focusers? Is there some advantage to them over the center focus? Thanks for any input.
Keith
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Andresin150
sage
Reged: 08/14/07
Posts: 305
Loc: Bogotá - La Calera / Colombia
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Individual focus allows sharper focus, and its easier to use since there is only one setting needed once you achieved focus (infinity). It is also more stable (more difficult to accidentally change it). It also makes easier to seal the binoculars for waterproof capabilities, but you'll also find CF waterproof binoculars.
Center focus is faster to use and may be preferred for observers that observe targets that constantly change relative distance such as bird watchers.
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Jeronimo Cruz
super member
Reged: 09/01/08
Posts: 141
Loc: Tucson, AZ
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Andresin150 hit the nail on the head!
If your intent is personal astro observation, IF is the way to go. Having said that, I prefer well made center focus binoculars because of thier flexabilty for both day and night use. Have you ever tried to focus IF e.p.'s on an airplane flying overhead? Also, individually focusing e.p.'s are too time consuming for public viewing or just sharing binoculars with someone.
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Jeronimo
TeleVue 101 + Gibralter
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harbinjer
super member
Reged: 12/17/08
Posts: 126
Loc: Southeastern Minnesota
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Another thing that might be obvious: it is easier to use center focus while hand holding. It can be a benefit to mount IF binoculars, if only to focus them correctly.
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Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3469
Loc: Cambridge, MA, USA
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Quote:
Why is it that many astro binos have individual focusers? Is there some advantage to them over the center focus? Thanks for any input.
Individual focus is much simpler and more robust from a mechanical standpoint. Center focus basically requires three different sliders to work as one -- two for the eyepieces, one for the focuser. Even if you machine them perfectly, you still have to leave a little room between the eyepieces and their sleeves to let them slide freely.
With individual focus, by contrast, the eyepieces mate tightly to the tubes, vis a threaded surface. You can't get any simpler or more robust than that.
On the other hand, I find center focus vastly easier to use. I tweak the focus on all my astro instruments constantly, and I don't want to have to use two hands to do so. So I view it as a tradeoff between human engineering and mechanical engineering.
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Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
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BobinKy
Carpal Tunnel
Reged: 04/27/07
Posts: 1683
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I find center focus usually delivers a finer focus (depending upon the binocular) because I am adjusting the focus mechanism with both eyes looking through the binocular (larger impression in my brain). With individual focus I adjust the focus mechanism while looking through the binocular with only one eye at a time.
. . .
A sailor standing on deck, the ship tossing in the waves, salty spray biting his face, one arm hanging onto the rusty railing--this sailor would most certainly press a pair of individually focused binoculars into his eye sockets--once focused, always in focus.
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Bob
38°N
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Prof M
member
Reged: 07/26/09
Posts: 49
Loc: Southwest Utah
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Thanks for explaining the comparative benefits of each type of focusers. It s a big help.
keith
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