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Dumb Question of the Day-FOV calculation |
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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That makes perfect sense. But it seems like that blows a hole in your previous statement about the field of view doubling when the distance doubles. Otherwise, every scope would have to have the same FOV.
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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This makes no sense. Please elaborate. |
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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As stated earlier, the FOV on any scope represents a triangle from your scope, to whatever distance we're talking about, be it 100 yards, 200 yards, etc. There is only one triangle in which base (FOV) doubles when the altitude (distance to target) doubles, and that is a right isosceles triangle. Therefore, if that is the ONLY triangle with which the FOV could double as the distance doubles, then every scope would have to have pretty much the same FOV, otherwise, it couldn't be a right isosceles triangle.
Make sense? |
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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..meaning to fit into your theory of the FOV of any scope doubling when the distance doubles, they would all have to have a FOV that represents a right triangle, which would mean they would all have to be the same.
This is obviously not the case, so therefore I believe your theory is flawed. |
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billyburl2
Optics Master Extraordinaire Joined: January/08/2009 Location: Cottonwood, AZ Status: Offline Points: 4015 |
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Unless of course each scope starts out with a different base FOV, because of the internal prescription of the lenses and how it was put together... Each scope will react to distance exactly the same, it's how the scope is designed and built that sets the initial parameters.
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If it is tourist season, why can't we shoot them?
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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That is slightly correct and mostly flat out wrong. The FOV is an angle. The projection of it onto a plane a particular distance away from the vertex forms a triangle. That is typically an isosceles triangle (though not necessarily, since I have seen plenty of scopes with asymetric FOV due to manufacturing tolerances). However, the angle at the vertex, varies considerably from scope to scope and from magnification to the magnification. The distance to the target plane is the height of the triangle and for ANY triangle, isosclees or otherwise, the length of the opposite side of the triangle (which is the FOV in this cases), doubles if you double the height of the triangle. That is VERY basic geometry. I am guessing that you are confusing isosceles triangle with an equilateral triangle. In an equilateral triangle, the angle at the vertex is always 60 degrees. Aside from the geometrical considerations, what does any of this have to do with the diameter of the objective lens? ILya
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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Once again, right triangle and equilateral triangle are not the same. And for the record, this is not my personal theory. This is how geometrical optics works. I work withoptical instruments for a living and how FOV works is pretty well established. ILya
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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Right...but my point remains the same. If each scope has a different "base FOV" as you put it, then it's impossible for every scope's FOV to double when the distance doubles as Koshkin suggests.
...or were you referring to something else? |
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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I never said "right triangle". Re-read my post. I said "right isosceles" triangle. BIG difference. Let's start from scratch. Do you disagree that a scope's field of view represents an isosceles triangle? |
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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Perhaps this will help. Click on the link below and tell me where I'm wrong. Perhaps I'm missing something...
Click on the link below (or copy and paste if you can't click on it) http://www.mathopenref.com/isosceles.html Point "A" represents the scope, or perhaps your eyeball, or whatever. (Yes, I realize that the FOV will never come to a sharp point like the tip of the triangle, but I think this still makes my point). The distance between "B" and "C" in the illustration represents the FOV. The "altitude" figure on the left would represent the distance to the target. There is only ONE case in which the base of the triangle would be double the altitude, and that is when the angle at "A" is 90 degrees. Drag point "A" down so that the altitude is 18 (Half the base which is 36) to see what I mean. With the angle at "A" set at 90 degrees, the base would double to 72 (double the original 36) if you doubled the altitude to 36, and it would continue to double as the distance doubled. ANY other angle at "A" would NOT result in the base doubling as the altitude doubles. Therefore, it doesn't seem as though the FOV on every scope would double as the distance doubles, unless the peripheral vision while looking through the scope was not a straight line like the sides of a triangle, but rather a curved line similar to a parabola if the angle was greater than 90 degrees, and a line that curves the opposite way if less than 90 degrees. http://www.mathopenref.com/isosceles.html |
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Dogger
Optics Jedi Master Joined: January/02/2007 Location: Ontario, Canada Status: Offline Points: 8921 |
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I think you had better listen to Ilya on this one otherwise your thread title risks becoming a self fulfilling prophecy. If you use your triangle calculator you will see how doubling the altitude will double the base as long as you keep the angle at "A" constant.
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God save the Empire!
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billyburl2
Optics Master Extraordinaire Joined: January/08/2009 Location: Cottonwood, AZ Status: Offline Points: 4015 |
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THIS! Some scope manufactures even post FOV numbers in degrees. This is the one constant that is fixed by the design of the scope.
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If it is tourist season, why can't we shoot them?
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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You are right! I concede! |
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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I am not trying to be mean, but there are a few things you are missing, most notably geometry and optics.
How did you get an idea that the the linear FOV at a particular distance is double the distance to the target? There isn't a riflescope in existence for which that is accurate. Using your terminology, if you double the altitude of the triangle, the distance from B to C, assuming the angles remain the same, will double. ILya
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Urimaginaryfrnd
MODERATOR Resident Redneck Joined: June/20/2005 Location: Iowa Status: Offline Points: 14964 |
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So let me get this straight. Point A times point B may or may not equal point C except on alternate Thursdays when a lunar eclipse occurs at which time the point may become pointless or inversely proportional in clarity to M.U.D. (Miscelaneous Undocumented Devices). Therefore in theory: The closer you are to chit, the less chit you can see, and the farther you are from chit the wider range of chit you can see, which means that an optic on an orbiting satelite can see a world of chit.
Edited by Urimaginaryfrnd - December/28/2014 at 19:46 |
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"Always do the right thing, just because it is the right thing to do". Bobby Paul Doherty Texas Ranger |
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Voodoo6
Optics Apprentice Now With Kung-Fu Grip! Joined: March/29/2009 Location: United States Status: Offline Points: 213 |
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I plumb guess I gots ma gizzintus mixed up with ma ciphering.....
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"A prisoner of the white lines on the freeway"
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Trailblazer
Optics GrassHopper Joined: July/15/2014 Status: Offline Points: 34 |
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That's exactly what happened! |
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Rancid Coolaid
MODERATOR Joined: January/19/2005 Location: United States Status: Offline Points: 9318 |
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Science is hard.
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Freedom is something you take.
Respect is something you earn. Equality is something you whine about not being given. |
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RifleDude
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Ted
Money can't buy happiness... but it's much more comfortable to cry in a Porsche than on a bicycle. |
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Peddler
Optics God Joined: July/04/2012 Location: Oswego,NY Status: Online Points: 13533 |
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When you are dead, you don't know you are dead.It is difficult only for others.
It is the same when you are stupid. |
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