OpticsTalk by SWFA, Inc. Homepage SWFA     SampleList.com
Forum Home Forum Home > Scopes > Rifle Scopes
  New Posts New Posts RSS Feed - Dumb Question of the Day-FOV calculation
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Visit the SWFA.com site to check out our current specials.

Dumb Question of the Day-FOV calculation

 Post Reply Post Reply Page  <123>
Author
Message
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 16:40
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.
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 16:45
Originally posted by Trailblazer Trailblazer wrote:

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.


This makes no sense. Please elaborate.
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 17:04
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?
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 17:06
..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.
Back to Top
billyburl2 View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: January/08/2009
Location: Cottonwood, AZ
Status: Offline
Points: 4015
Post Options Post Options   Thanks (0) Thanks(0)   Quote billyburl2 Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 17:26
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.
If it is tourist season, why can't we shoot them?
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 17:49
Originally posted by Trailblazer Trailblazer wrote:

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?

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
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 17:52
Originally posted by Trailblazer Trailblazer wrote:

..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.

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 
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 19:10
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?
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 19:13
Originally posted by koshkin koshkin wrote:


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 


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?
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 19:30
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

Back to Top
Dogger View Drop Down
Optics Jedi Master
Optics Jedi Master
Avatar

Joined: January/02/2007
Location: Ontario, Canada
Status: Online
Points: 8912
Post Options Post Options   Thanks (0) Thanks(0)   Quote Dogger Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 20:39
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.
God save the Empire!
Back to Top
billyburl2 View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: January/08/2009
Location: Cottonwood, AZ
Status: Offline
Points: 4015
Post Options Post Options   Thanks (0) Thanks(0)   Quote billyburl2 Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 20:48
Originally posted by Dogger Dogger wrote:

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.
THIS!
Some scope manufactures even post FOV numbers in degrees. This is the one constant that is fixed by the design of the scope.
If it is tourist season, why can't we shoot them?
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 20:51
Originally posted by Dogger Dogger wrote:

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.


You are right!  I concede!
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: December/27/2014 at 20:52
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
Back to Top
Urimaginaryfrnd View Drop Down
MODERATOR
MODERATOR
Avatar
Resident Redneck

Joined: June/20/2005
Location: Iowa
Status: Offline
Points: 14964
Post Options Post Options   Thanks (0) Thanks(0)   Quote Urimaginaryfrnd Quote  Post ReplyReply Direct Link To This Post Posted: December/28/2014 at 00:59
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

"Always do the right thing, just because it is the right thing to do".
Bobby Paul Doherty
Texas Ranger
Back to Top
Voodoo6 View Drop Down
Optics Apprentice
Optics Apprentice
Avatar
Now With Kung-Fu Grip!

Joined: March/29/2009
Location: United States
Status: Offline
Points: 213
Post Options Post Options   Thanks (0) Thanks(0)   Quote Voodoo6 Quote  Post ReplyReply Direct Link To This Post Posted: December/28/2014 at 07:47
I plumb guess I gots ma gizzintus mixed up with ma ciphering.....

"A prisoner of the white lines on the freeway"
Back to Top
Trailblazer View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/15/2014
Status: Offline
Points: 34
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trailblazer Quote  Post ReplyReply Direct Link To This Post Posted: December/28/2014 at 08:45
Originally posted by Voodoo6 Voodoo6 wrote:

I plumb guess I gots ma gizzintus mixed up with ma ciphering.....




That's exactly what happened! Big Grin
Back to Top
Rancid Coolaid View Drop Down
MODERATOR
MODERATOR
Avatar

Joined: January/19/2005
Location: United States
Status: Offline
Points: 9318
Post Options Post Options   Thanks (0) Thanks(0)   Quote Rancid Coolaid Quote  Post ReplyReply Direct Link To This Post Posted: December/30/2014 at 10:01
Science is hard.
Freedom is something you take.
Respect is something you earn.
Equality is something you whine about not being given.
Back to Top
RifleDude View Drop Down
MODERATOR
MODERATOR
Avatar
EVIL OPPRESSOR

Joined: October/13/2006
Location: Texas
Status: Offline
Points: 16337
Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: December/30/2014 at 11:35
Ted


Money can't buy happiness... but it's much more comfortable to cry in a Porsche than on a bicycle.
Back to Top
Peddler View Drop Down
Optics God
Optics God
Avatar

Joined: July/04/2012
Location: Oswego,NY
Status: Offline
Points: 13526
Post Options Post Options   Thanks (0) Thanks(0)   Quote Peddler Quote  Post ReplyReply Direct Link To This Post Posted: December/30/2014 at 11:38
Big Grin
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.
Back to Top
 Post Reply Post Reply Page  <123>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.633 seconds.