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is there an optimal eye relief ???

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RifleDude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:12

Originally posted by Dolphin Dolphin wrote:

Ted, actually, the larger the objective, the smaller the FOV.  The difference, compared to other variables may not be as great, but it is true.

 

Sorry, but objective diameter affects light transmission and resolution, but not FOV.  While it's true that larger objectives generally come with greater magnification, and greater magnification means smaller FOV, objective diameter in and of itself has no effect on FOV.  FOV is influenced by ocular lens diameter, magnification, and focal length.



Edited by RifleDude
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Roy Finn Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:13
As far as the two Leupold scopes I just checked on are concerned, I compared a 3.5-10x40 and a 50mm and the FOV at 10x is the same. Same result with the 4.5-14x40 and 50mm. Me thinks Ted is on to something. Hey, what the heck, he was bound to be right about something.  

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Post Options Post Options   Thanks (0) Thanks(0)   Quote pyro6999 Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:19
come on guys anybody who can look through a scope can obviously see that the higher the  power the scope reaches the smaller of an area you are looking at think about it if you have a plain old 3x9 and say  6.5x24 put the scopes on there highest powers and look at  a target @ 100yds at 9x you will see the stand the target's attached too among other things @ 24x you will see target and thats about it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Roy Finn Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:29
I don't think that was the question. Someone asked if the objective lens size had any bearing on FOV when comparing like scopes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pyro6999 Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:33

i see but my comparison works for that as well, 3x9x50 and 6.5x24x50 the magnification difference is the factor for fov.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Roy Finn Quote  Post ReplyReply Direct Link To This Post Posted: October/23/2007 at 21:46
No question about that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dolphin Quote  Post ReplyReply Direct Link To This Post Posted: October/24/2007 at 11:22
What I should have said, is that all other things being equal, the larger the objective lens the smaller the FOV.  Think of it this way.  Whether the objective lens is large or small and depending on the properties of the lens, it has a potential to bring in light from 180 degrees.  The design of the lens limits this, but this is just for demonstration purposes.  Now for demonstration purposes, take two objective lens, one that is 10 feet in diameter, the other, the size of a dime.  As the beam of light is narrowed as it passes down the scope tube to relay lens is going to be more "cropped", on the larger lens, comparatively, despite the angle of entry being the same, because, the base subtended by that angle of entry is larger.  Therefore, it is more difficult, with the same optical design to get the same FOV.  However, obviously a different design will solve the problem, especially since we are not talking about differences in objective sizes as described.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/24/2007 at 14:45

Originally posted by Dolphin Dolphin wrote:

What I should have said, is that all other things being equal, the larger the objective lens the smaller the FOV.  Think of it this way.  Whether the objective lens is large or small and depending on the properties of the lens, it has a potential to bring in light from 180 degrees.  The design of the lens limits this, but this is just for demonstration purposes.  Now for demonstration purposes, take two objective lens, one that is 10 feet in diameter, the other, the size of a dime.  As the beam of light is narrowed as it passes down the scope tube to relay lens is going to be more "cropped", on the larger lens, comparatively, despite the angle of entry being the same, because, the base subtended by that angle of entry is larger.  Therefore, it is more difficult, with the same optical design to get the same FOV.  However, obviously a different design will solve the problem, especially since we are not talking about differences in objective sizes as described.

 

Sorry, Dolphin, but it doesn't work that way.  Even with all things being equal, objective lens diameter effects light transmission and in some cases resolution, but it has no effect on FOV.  The only reason you see some large objective scopes having more narrow FOV is because generally the larger objective diameter scopes are also higher magnification scopes. The larger objective is there to maintain a reasonably large exit pupil.  A longer focal length narrows FOV, and higher magnification also generally means longer focal length.  So, the presence of the large objective doesn't effect the FOV, the longer focal length and higher magnification does.  It just so happens that such scopes also have the larger objective. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dolphin Quote  Post ReplyReply Direct Link To This Post Posted: October/24/2007 at 15:21
Originally posted by RifleDude RifleDude wrote:

Originally posted by Dolphin Dolphin wrote:

What I should have said, is that all other things being equal, the larger the objective lens the smaller the FOV.  Think of it this way.  Whether the objective lens is large or small and depending on the properties of the lens, it has a potential to bring in light from 180 degrees.  The design of the lens limits this, but this is just for demonstration purposes.  Now for demonstration purposes, take two objective lens, one that is 10 feet in diameter, the other, the size of a dime.  As the beam of light is narrowed as it passes down the scope tube to relay lens is going to be more "cropped", on the larger lens, comparatively, despite the angle of entry being the same, because, the base subtended by that angle of entry is larger.  Therefore, it is more difficult, with the same optical design to get the same FOV.  However, obviously a different design will solve the problem, especially since we are not talking about differences in objective sizes as described.

 

Sorry, Dolphin, but it doesn't work that way.  Even with all things being equal, objective lens diameter effects light transmission and in some cases resolution, but it has no effect on FOV.  The only reason you see some large objective scopes having more narrow FOV is because generally the larger objective diameter scopes are also higher magnification scopes. The larger objective is there to maintain a reasonably large exit pupil.  A longer focal length narrows FOV, and higher magnification also generally means longer focal length.  So, the presence of the large objective doesn't effect the FOV, the longer focal length and higher magnification does.  It just so happens that such scopes also have the larger objective. 

Ted, I quess we will have to agree to disagree on this one.  My explanation can be better done with equations, but then again that  would be more complicated and I would have to do alot more home work than I am willing to put forth.  Lets see what Koshkin has to say about the topic.  I am almost sure I have heard him say that the larger the objective, the smaller the FOV, with all other things being equal.  Anyway, no big deal. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graysteel Quote  Post ReplyReply Direct Link To This Post Posted: October/24/2007 at 15:51
I am curious about this discussion. Could it be that there are differing assumptions at play? It seems to be that if the 'all things being equal' refers to focal length we may get one answer, and if 'all things being equal' refers to focal ratio we may get another. Or maybe I am the one not understanding. :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dolphin Quote  Post ReplyReply Direct Link To This Post Posted: October/24/2007 at 15:58
Bottom line, of all the things that affect the FOV, the objective size has the least affect with all things being equal, which is seldom the case and therefore the subject is mute and I should have never mentioned it and kept my big dumb mouth shut.  I have this habit of flapping it too much and instead of getting to the major points, drifting to minor details.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote timber Quote  Post ReplyReply Direct Link To This Post Posted: October/26/2007 at 15:12

Originally posted by cyborg cyborg wrote:

Roo, 3.2 of eye relief should be acceptable with up to a 300 win mag. If your shooting posture is correct. I know of two people shooting 300 RUM with only 3 inches of eye relief, They do shoot all the time though, and their posture is nearly flawless.

 

Lots of good technical information in this discussion.  But I gotta tell you I've brushed my eye/brow/forehead any number of times trying to get a shot off fast.  And that's with standard calibers in sporter weight rifles with scopes of 3.6 inches or more of eye relief.  No way would I shoot these same rifles with scopes/eye reliefs of 3 inches or less, especially not one chambered for 300 ultra.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote cyborg Quote  Post ReplyReply Direct Link To This Post Posted: October/26/2007 at 15:17
I'm shooting a 300 win mag hot hand loads, and never a bump except one time, I was scope hugging, and mine is 3.0 inches. The bump kinda surprised me but no blood and hardly a bruise, course I do have a head like a brick. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale Clifford Quote  Post ReplyReply Direct Link To This Post Posted: October/26/2007 at 15:48
It depends also, (and more so, I think) on how firm the gun is held against the shoulder. My regular gun is a 416 rem. mag. in a safari win. and it will get you every time, if you don't "snug it down".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote timber Quote  Post ReplyReply Direct Link To This Post Posted: October/26/2007 at 23:44

Can't say I've ever shot a 416.  Maybe with a new Swarovski Z6 1-6 with extended eye relief (4.72") I'd give it a try.  Ha ha.  I'm pretty much a chicken though when it comes to heavy recoiling rifles with scopes.  Shotguns no problem - there's just something about a scope on a big rifle that gives me pause. 

 

You're right about proper shouldering of course - get in a hurry and get a bruised shoulder, or worse.Unhappy  I'm fortunate I've never taken a scope hit - just baby kisses.  Enough to make me pay attention though!

 

 

 

 

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