How to Convert Linear Into Angular Field of View?

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Refractordude
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How to Convert Linear Into Angular Field of View?

#1

Post by Refractordude »


From Linear to angular in degrees. I searched the WWW, but could not find it. Thanks all
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Refractordude
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Re: How to Convert Linear Into Angular Field of View?

#2

Post by Refractordude »


I found this calculator, but can not understand how to use for the answer that I want.

https://astronomy.tools/calculators/binoculars
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sdbodin United States of America
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Re: How to Convert Linear Into Angular Field of View?

#3

Post by sdbodin »


Arc tan 122/1000 = 6.96, almost 7 degrees. The 122 is 366/3. Watch the units.

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Re: How to Convert Linear Into Angular Field of View?

#4

Post by Refractordude »


sdbodin wrote: Sat Dec 19, 2020 10:38 pm Arc tan 122/1000 = 6.96, almost 7 degrees. The 122 is 366/3. Watch the units.

Steve
Why did you divide the 366 by 3? What if the number was 380? Thanks Steve
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KathyNS Canada
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Re: How to Convert Linear Into Angular Field of View?

#5

Post by KathyNS »


Refractordude wrote: Sat Dec 19, 2020 10:47 pm
sdbodin wrote: Sat Dec 19, 2020 10:38 pm Arc tan 122/1000 = 6.96, almost 7 degrees. The 122 is 366/3. Watch the units.

Steve
Why did you divide the 366 by 3? What if the number was 380? Thanks Steve
Feet to yards. You can't mix units. Both have to be feet or both yards.
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Re: How to Convert Linear Into Angular Field of View?

#6

Post by sdbodin »


Also using arc sin works too and just multiplying by 57.3 ( one radian) yields the same result, all within a few decimal points. All are an approximation to the rigorous solution and work well for angles less than about a dozen degrees.

Arc sin 122/1000 = 7.01 degrees
57.3*122/1000 = 6.99 degrees

So, just round off, 7 degrees a standard fov for binos.

Now, if you want the apparent fov, just multiply the true fov by the magnification.

7*10 = 70 degrees

A wide angle bino view.

Hope this helps,
Steve
Scopes; Meade 16 LX200, AT80LE, plus bunch just sitting around gathering dust
Cameras; Atik 460ex mono, Zwo ASI1600MC-cool, QHY5L-II color and mono
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Re: How to Convert Linear Into Angular Field of View?

#7

Post by turboscrew »


It doesn't make much difference here, but I think the linear field is really 183ft (=366 ft/2) both ways around the normal..
It should be calculated: angle = 2*arc tan((366/6)/1000). (366/3 = feet to yards, and that halved is one-sided field width.)
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Re: How to Convert Linear Into Angular Field of View?

#8

Post by John Baars »


Rule of thumb. Approximation.

One degree is 17,45 at 1000 distance, no matter what unit you use. The units should be the same.
A field of 17.45 at 1000 is one degree.
A field of 144 at 1000 is 8.25 degrees

144 m at 1000m is 8.25 degrees
144 yards at 1000 yards is 8.25 degrees
144 feet at 1000 feet is 8,25 degrees.

In a yard there are three feet.
48 yards at 1000 feet is 8,25 degrees ( multiply the yards by 3 to become feet)


Maths behind it:
Imagine an object at 1000 units distance.
This is the radius of a circle.
The outline of the circle is Pi.2r
3,1415 X 2 X 1000= 6283 units
A circle has 360 degrees
One degree is 6283 units divided by 360 = 17,45 units
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