Binoculars field of view in degrees

Thanks. : )

FOV= (182*ft/3000*ft)*57.3=3.5 degrees

Jon

What's the problem? You've got all the information you need.

If the field is 182' at 3000', then the angle is (to an excellent
approximation:

182/3000 = 0.061 radians = 3.5 degrees

A rather small field of view, as you'd expect from an excessively high
magnification!

Regards,

Chris

Well...now I do : )

Geez. Is that all I needed to do?

Thanks! Now I have "measured" proof of what I see and you're right. Small
field of view for constellations. Not bad for the moon though.

Thanks for helping an old fart out Chris. ; )

-Bob

Thanks Jon

-Bob

Sorry, Bob; on reading my reply to you it sounds rather abrupt. It wasn't
intended to be that way; please excuse me!

Regards,

Chris

Heh. Thanks Chris. Actually, I know it must be frustrating for you and the
other very helpful and well informed guys in this group to answer the
obvious and perhaps simple questions. I'm just thankful for a resource like
this and for your taking the time to respond.

A follow-up if I may. Do you or anyone else know of a good site or internet
resource for _basic_ telescope optic formulas such as what you shared? I'm
a noob to this (quite obviously) and would be more interested in "less
academic/more lay-person friendly" sort of info. I did make use of Google
and found a few links but didn't know if anyone has a favorite or two. Many
thanks.

-Bob

Further, apparent field is that times the magnification, or in this case 3.5
* 16 = 56 degrees.

Apparent field is about 50 for conventional binoculars, 60 or 70 for
wide-angle ones.

Conventional ones are sharper.

Wide-angle binoculars can have narrow Afov eyepieces and Narrow angle
binoculars can have wide Afov eyepieces. Except at the narrowest and
widest extremes of True field of view, there is no standard rule you
can follow.

The way I have arranged these groups is based on personal use
preference. You may think otherwise, but my thoughts are after
hundreds of hours of use.

Most binoculars do not actually measure in the field what is stated
for Tfov. Usually the higher cost premium binoculars do measure as
stated.

Half of all binoculars I measured have Afov eyepieces between 60° and
65°. They cross a range from narrow to wide True field of view.
There are some but few wider eyepieces in use.

What may seem like a narrow 4° field of view would be wide for a 15x
or 16x binocular. A 3.5° field of view would be wide for a 20x
binocular.

On the other hand, a True field of view less than 3.0° is extremely
narrow for ANY binocular.

Some wide Afov eyepieces have excellent performance. Fujinon 16x70
and Oberwerk 15x70 use 64° Afov eyepieces and are sharp to 80%+ Tfov.
In comparison, Orion 16x80 uses a narrower 53° Afov eyepiece and its
sharpness characteristics are poor in the outer 40% Tfov.

Some of the newer 22x and 25x binoculars coming on the market are
advertised as 3.5° Tfov, but are measuring less than stated. If the
newer 22x an 25x binoculars measure over 3.0° Tfov, they are using
eyepieces with Afov approx. 66° to 75°, wider eyepieces than anything
I have seen to date.

The 8x binoculars with a 6.5° field of view may be considered the low
end of a wide True field of view for that power binocular. This Tfov
is not produced with a wide Afov eyepiece. They are sharp to 80% of
the True field of view.

edz

NARROW True Field of View
Pentax PCF V 20x60 Tfov 2.2 Afov 44
Pentax PCF V 16x60 Tfov 2.8 Afov 45
Orion Giant 16x80 Tfov 3.3 Afov 53
Oberwerk Deluxe 20x80 Tfov 3.3 Afov 65

STANDARD True Field of View
Fujinon FMT-SX 16x70 Tfov 4.0 Afov 64
Pentax PCF III 12x50 Tfov 4.2 Afov 50
Oberwerk 15x70 Tfov 4.3 Afov 64
Nikon S&E Kestrel 10x50 Tfov 4.9 Afov 49
Minolta Standard XL 12x50 Tfov 5.1 Afov 61

WIDE True Field of View
Orion Ultraview 10x50 Tfov 6.0 Afov 60
Orion Vista 8x42 Tfov 6.5 Afov 52
Swift Ultralite 8x42 Tfov 6.6 Afov 53
Minolta Standard XL 7x35 Tfov 9.0 Afov 63
Minolta Activa 7x35 Tfov 9.3 Afov 65

NARROW Apparent Field of View
Pentax PCF V 20x60 Tfov 2.2 Afov 44
Pentax PCF V 16x60 Tfov 2.8 Afov 45
Nikon S&E Kestrel 10x50 Tfov 4.9 Afov 49
Pentax PCF III 12x50 Tfov 4.2 Afov 50
Orion Vista 8x42 Tfov 6.5 Afov 52
Swift Ultralite 8x42 Tfov 6.6 Afov 53
Orion Giant 16x80 Tfov 3.3 Afov 53

WIDE Apparent Field of View
Orion Ultraview 10x50 Tfov 6.0 Afov 60
Minolta Standard XL 12x50 Tfov 5.1 Afov 61
Minolta Standard XL 7x35 Tfov 9.0 Afov 63
Fujinon FMT-SX 16x70 Tfov 4.0 Afov 64
Oberwerk 15x70 Tfov 4.3 Afov 64
Minolta Activa 7x35 Tfov 9.3 Afov 65
Oberwerk Deluxe 20x80 Tfov 3.3 Afov 65

Not as I understand it. Binoculars are not called wide-angle unless the
field of view is wide *relative to their magnification*. That means wide
AFOV, always.

For example, 6x binoculars with a 7-degree field are not wide-angle, but 10x
binoculars with a 7-degree field definitely are wide-angle. The AFOVs are
42 and 70 degrees respectively.

Some cheap binoculars may be labeled "wide-angle" regardless of their field.

--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

Hi Michael,

From practical experience I find binoculars over 6° Tfov are wide.
Doesn't seem to matter much whether they are 10x or 8x, they're fairly
wide. Looks wide to me, so I call it wide. I use a lot of different
binoculars and that's my experience. A 15x binocular that is 4.3° is
wide. On the other hand a 12x binocular that is only 4° seems pretty
darned narrow. As I said, I know there are some out there (11°Tfov),
but I've never seen a pair of binoculars with a 70°Afov eyepiece.
I've got more than a dozen fairly common examples in my list, none are
really cheap brands and several provide a nice wide view.

Practical sizes on the market available to the average user in the 8x
to 10x range are often about 6° to 6.5°. These give a nice wide field
of view. I know there's some 8x binocs that have and 8° Tfov, that's
really wide. But I'd suggest to anyone that the Orion Ultraview 10x50
or the Swift Ultralite 8x42 are a decent widefield binocular, great
choices for the user who wants to see a lot at once.

The Swift Ultralites have a 52° eyepiece. You could say, strictly
speaking, that eliminates them from qualifying as a widefield
binocular. But take one look through them and notice they have a nice
wide field of view, great for scanning large areas, much better than
any 5° or 4° binocular. So I call them widefield.

I think my viewpoint is there are combinations that don't fit the mold
and don't be led to believe one or the other eyepiece is always going
to give you a similar end result view. Afov doesn't always equate to
an similarly perceived Tfov.

edz

I have a pair of Celestron Birdwatchers, multicoated BAK 4 prisms, 7x35's with
a 7 foot close focus and a 10 degree FOV.

A bit short on the eye relief mostly because of that Wide Field view. I have
checked the TFOV against known star separations and it does seem to be 10
degrees.

I tend to notice the AFOV when looking through the binoculars, it is pretty
clear to me when the AFOV is narrow or when it is wide.

When using the bino's the TFOV really determines how easy it is to spot stuff.

jon

But standard 7x50 binoculars have a 7-degree field and are not labeled
"wide-angle". To the manufacturers and dealers, "wide-angle" means "a wider
angle than the usual binoculars of this magnification." In practice it
means "apparent field appreciably more than 50 degrees."

I'm not talking about whether it seems wide to you -- I'm talking about the
meaning of the term in product descriptions.

There are normal 7x binoculars and wide-angle 7x binoculars. Likewise there
are normal 12x binoculars and wide-angle 12x binoculars. The true field of
the wide-angle 12x may well be less than the true field of the ordinary 7x.

> But standard 7x50 binoculars have a 7-degree field and are not labeled

Michael, I have to agree with you. The way various binocs are sold
and how I perceive the fov can sometimes be quite different.
Sometimes I may as many as three or four differnt binoculars set up
outside. My perception is most definitely swayed by in practice use
and comparison of one fov to another, not by how they are sold. A 6
degree field can look downright wide to me when I've just moved over
from a 4 degree field.

The other important note you make and as I said earlier is that what
is considered wide can vary considerably with power. My 12x Pentax at
4.0° are very narrow, but my 16x Fujinon at 4.0° seems quite wide.
The true field of some high powered binocs that seems wide can be less
than some lowered powered normal field binocs.

edz