Garfield
sage
Reged: 02/02/04
Posts: 210
Loc: South-Western ON Canada
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Hello All! I know this is a subjective question, but with all the experience lurking around here, I thought I'd see if there was some sort of consensus on what is considered an "optimum" FOV for astro binocular observing, keeping in mind the inevitable trade offs with objective size and power.
From my experience, a 3.5° - 4.5° FOV seems to be "optimum" to catch and frame the vast majority of the most popular binocular objects at the low powers that typical astro binoculars provide. This roughly translates a bino with 12x-20x power and 60mm-80mm objective or there-abouts, with the ever popular 15x70's right in the middle.
It appears to me that the < 3° FOV from 25x100mm binos provide neither the wide FOV desireable nor the high powers often wanted for specific objects - i.e. the worst of both worlds. After all, 100mm aperture is considered small in the world of astronomy, and if FOV is not important, then presumably one would haul out a full-blown telescope with binoviewer and lay some real aperture and power on the object.
At the other end of the spectrum, to gain wider FOV you have to sacrifice aperture and power to catch what amounts to a very small number of extended objects which seems to high a price to pay.
Opinions? 
BTW, I am considering tracking down one of those 62mm or 77mm Miyauchi Owletts from Japan. I like the idea of interchangeable eyepieces and wide FOV (as compared to the narrower FOV of the 45° Miyauchi's), but am wondering if I will miss not having more aperture.
Thanks!
Gary in Ontario
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AT66ED
Pentax Papilio 6.5x21 ●
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ArizonaScott
Postmaster
Reged: 04/29/04
Posts: 5030
Loc: Phoenix, AZ
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3.5 at 20X. Seems to be just the right mag+FOV to view galaxies and other DSO's while providing a nice background to frame the view. Did I pass the test
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Scott
10" LX200 Classic, Konus 200, Orion ST80, ETX90 OTA, 60mm Celestron alt-az, Obie 20x80's, Meade 10x50's
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lighttrap
Reged: 02/06/04
Posts: 3833
Loc: cloudy, foggy, humid NC, US
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I really struggle justifying, or even simply enjoying, binoculars with less than a 3.5* FOV. Even just dropping down to 2.8-3* really takes away some of the enjoyment factor. To me, dropping the FOV that low is the province of scopes. With binoculars, I prefer a 4-5* FOV to get that wide expansive feeling.
Mike Swaim
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18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Mounted? for me the total fov becomes a non factor.
Hand held, I like 4.0+ degrees.....
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KennyJ
Reged: 04/27/03
Posts: 10146
Loc: Lancashire UK
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I am currently working on a very personal "theory" about an aspect of binocular viewing that is closely related to this question.
I am attempting to put some numbers to what I loosely define as the "WOW FACTOR".
My aim is to formulate an easy to understand "mathematical formula" for "optimum two -eyed viewing".
This will always be relative to what one is looking AT , and what one would like to "see" -- but I think I'm getting somewhere with a basic "summary formula".
Blue W does make a valid point with the difference between a hand -held binocular and a mounted instrument.
There also comes a point in both magnification AND field of view , whereby some sort of "finder" becomes desireable.
I suggest that a binocular that requires a "finder" of any sort ought to be placed in a separate "category" from a binocular that can be enjoyably utilised as a "stand -alone" instrument.
I think that Arizona's summary of "20x and 3.5 TFOV" is quite close to "optimum" -- i.e 70 degree AFOV.
But how many 20x binos ACTUALLY provide a TRUE 3.5* TFOV ?
If we can quote one , then that is probably very close to as good as it's going to get -- all things considered.
An interesting question which I hope attracts many replies.
Clear skies -- 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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sftonkin
sage
Reged: 02/25/04
Posts: 395
Loc: Kent, UK
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Depends on what you mean by "binoculars" 
Recently, binoculars have meant at least three different things for me:
(a) Something for scanning the sky/refreshing my memory about star-hops/working out star-hops as a prelim tousing a larger instrument. For this I like a very large FoV; my 10x50 Swift Newport has 8.2 deg. The edge is lousy, the BK7 prisms consume a lot of light, and the entire FoV is vignetted, but they are still good for the purpose. The large FoV was also useful for the transit, when I had them mounted, as it enabled inexperienced youngsters to find the Sun more easily and, once it was found, it stayed in the FoV for longer.
(b) Good quality hand-holdable binocs for "grab and go" semi-serious observing when I want the optical quality. For this I like 5 deg in a 10x binoc. For years I have worked out star-hops based on 5 deg FoV, so this FoV has become "familiar".
(c) Mounted big bins as a "main" instrument. I concur with BluewaterObserva on this -- FoV is a non-issue. I tend to use the Rigel QuikFinder to hop to the right location (I'm learning 2 deg hops), then take it from there.
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Stephen
Hindsight: The only truly diffraction-limited system
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Gary:
I use binoculars in two modes for astronomy -- my favorite approach is handheld observing and for that I like a big FOV. I use Nikon Venturer LX 8x42s, which have an FOV of 7 degrees.
I also have a pair of Orion MegaView 20x80mm binos with a 3.5 degree FOV. I like these for mounted observing.
I tried out a pair of Celestron 25x100s at a star party last year and wasn't too impressed -- I think because of the narrow FOV. A couple of years ago I had the chance to try some Fujinon 40x150s and wasn't overwhelmed by them either. I mean, they were nice, but not THAT nice.
Apparent field of view is also important. I've found that binos with an apparent fov of less than about 60 degrees are less enjoyable for me. (I've been spoiled by Tele Vue eyepieces, I guess.)
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Quote:
I am attempting to put some numbers to what I loosely define as the "WOW FACTOR".
So, will this be the KennyJ Wow Factor Index? I'm told they have an index for everything.
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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KennyJ
Reged: 04/27/03
Posts: 10146
Loc: Lancashire UK
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Fiske,
I too consider "about 60 degrees" to be something of a "lower limit of acceptability" when it comes to AFOV of binoculars.
I note that your beloved Nikons have only a 56 degree AFOV.
As regards my forthcoming WOW INDEX , I have little doubt that the formula will be UNIVERSALLY accepted , at least in THIS household :-)
Regards , 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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Anonymous
Unregistered
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A WOW Index Factor, WIF...that's cute. This "[blank] index factor" craze is getting out of hand!
Prefered FOV? Well, I guess I don't have one. It all depends on what type of observing I am doing. For high mag. the FOV is going to shrink...that's ok for me if a high mag. is what I want to use.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
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I'm not aware of any 20x80s on the market that actually measure more than 3.25°. The advertised 3.5° is not reached by any model I know of.
In the 22x100 to 25x100 range, binocs actually measure 2.8° down to less than 2.5°, none reach 3.0°.
I haven't found the need to use any sort of finder on any binocular with a filed of view down to about 2°. Viewing thru the binocs seems easier to me than veiwing thru a finder.
Handheld, I find my favorite Tfov is about 6°.
Mounted, my favorites are Oberwerk 15x70s at about 4.3° and Fujinon 16x70s at 4.0°
FOV is not as much an issue for me when I jump to higher powered binocular viewing in the 20x to 25x range. Sure the fov gets smaller, but the image scale gets a lot bigger and objects are easier to see. Since I don't seem to have much problem finding things, maybe that's what makes it a non-issue for me.
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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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Quote:
A WOW Index Factor, WIF...that's cute. This "[blank] index factor" craze is getting out of hand!
More or less my point.
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Quote:
I note that your beloved Nikons have only a 56 degree AFOV.
Regards , Kenny.
I guess 56 degrees must be my lower limit.
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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Garfield
sage
Reged: 02/02/04
Posts: 210
Loc: South-Western ON Canada
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Thanks everyone for the responses!
After reading all your posts, my take is that it would appear that a FOV in the 3.5°-4.5° range seems to be favoured by the majority here.
Although I understand the need for wider FOV when handheld as opposed to when mounted, nobody convinced me that a narrower FOV, mounted or otherwise, was actually desireable in a binocular. Moreover, comments tended to bolster my view that people tend to use large binos as small telescopes, rather than just as larger binoculars, if that makes any sense. In other words, there isn't much of a reason to have a pair of large binoculars (>=100mm) IF one already has a telescope equipped with a binoviewer (everything else being equal).
It still seems to me that a bino in the 70-80mm aperture range with interchangeable wide field eyepieces would be ideal. Unfortunately, Kevin B. informed me today that Miyauchi will not sell the Miyauchi Owlet's outside of Japan. That is a shame.
Gary in Ontario
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AT66ED
Pentax Papilio 6.5x21 ●
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craig_oz_land
sage
Reged: 01/21/04
Posts: 343
Loc: Sydney, Australia
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And the best bino in the 70-80mm range might be
http://www.kowascope.com/pro/bino/high/top.htm
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Takahashi FS-102
Fujinon FMT-SX2 7x50
Takahashi Astronomer 22x60
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Garfield
sage
Reged: 02/02/04
Posts: 210
Loc: South-Western ON Canada
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Hi Craig;
Yes, I considered those Kowas, but they have the same narrow FOV as the 45° Miyauchi's.
I still think the 77mm Owlet's have everything I'm looking for. What I need is to find a Japanese Miyauchi dealer that will ship to Canada! 
Gary
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AT66ED
Pentax Papilio 6.5x21 ●
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sftonkin
sage
Reged: 02/25/04
Posts: 395
Loc: Kent, UK
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I've never been a great fan of large AFoVs except as in (a) in my previous (this may be something to do with my favourite telescope eyepieces being decent orthoscopics). I like to be able to see everyting at onece, without feeling that I have to almost turn my head to look around the FoV. 50 deg AFOV does it for me. Things start looking too small below 45 deg.
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Stephen
Hindsight: The only truly diffraction-limited system
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craig_oz_land
sage
Reged: 01/21/04
Posts: 343
Loc: Sydney, Australia
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Gary,
They probably cost 4 times the 77s price which makes it an easier choice.
To keep on the topic, I think 65 degrees is about the most I would like. Although all of my eyepieces and binoculars are around 52 degrees or less.
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Takahashi FS-102
Fujinon FMT-SX2 7x50
Takahashi Astronomer 22x60
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Anonymous
Unregistered
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Gary, probably the aperture cutoff for binos vs. telescope is more like around 80mm than 100mm.
Your survey could go a step further with questions like, "Of the people who have telescopes, [blank]", then I think you could draw a better conclusion from responses. For instance, I don't have a 'scope AND having binos with 1 degree FOV is fine (and even desired at times).
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Garfield
sage
Reged: 02/02/04
Posts: 210
Loc: South-Western ON Canada
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Quote:
Your survey could go a step further with questions like, "Of the people who have telescopes, [blank]", then I think you could draw a better conclusion from responses. For instance, I don't have a 'scope AND having binos with 1 degree FOV is fine (and even desired at times).
Nightwatch: Good point, although I still think my conclusions are valid since I qualified my conclusion by saying IF one alreadly owned a telescope - admittedly after I posted my question, though.
My question was predicated on the belief that most astro binocular users already have one or more telescopes and that the binos merely supplement their observing hobby. Perhaps that assumption is not entirely accurate?
Gary
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AT66ED
Pentax Papilio 6.5x21 ●
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