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Dustyattic View Drop Down
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    Posted: January/26/2011 at 16:38

I have a few questions for the optics wizards here. Please educate me with facts.

What's the proper name for the perceived size of the disk you see through a riflescope? The size of the "hole" your eye views, in other words.  I'm pretty sure the phenomenon I am referring to is probably not directly related to exit pupil diameter.  I've noticed that scopes which are labeled "Wide Angle" seem to present a larger view.

For example, I have an old Tasco Pronghorn fixed power which I had on a junky .22 for years. Some time back, I was looking around for another cheapie scope to put on another .22.  All the low end scopes I looked at of equal objective size and magnification gave a narrower "peephole" like view.  I became more impressed with the old Tasco I had been using.

A while later, I was at a sporting goods store and looked through a Nikon and some others. I expected a scope of this price range to give a wider view than any of the scopes in my junk box, but I actually think my cheap Tasco gave a wider view than the Nikon.  Yes, the Nikon was on low power setting.  So what's the difference?

Of all the scopes I have looked through, I think some of the Swift, Bushnell, and I think Burris gave wider views than some higher end models.

Anyway, I'm getting away from the point.... What is the "perceived viewing area" called, and why isn't it listed in a scope's specifications? Especially since it's one of the top 2 or 3 things I look for when shopping for scopes.

This may be another way of asking the same question...  What's the difference in the lenses between a scope labeled "Wide Angle" and one which isn't?




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Post Options Post Options   Thanks (0) Thanks(0)   Quote BigGameBalls Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 16:55
Sounds like you're talking about Field of View to me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dustyattic Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 17:03
Maybe so.  I may experiment a little more, such as actually measuring the FOV of different scopes by counting the number of fence posts visible at one time at a distance, and compare that to the view angle I described above.

I had previously discounted FOV because I was simply looking at a blank white wall and noticing how much the scope "filled up" my eye.  I'll also try to find what the difference is between similar scopes which present different field of views.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote supertool73 Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 17:06
All scopes has a FOV listing.  That is hugely important for most people.  The lower the mag typically the larger the FOV.  Also the design of the scope can have some affect.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BigGameBalls Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 17:30
 The only way I know of to get a drastically larger FOV from a scope of the same magnification is to reduce the eye relief. The only exception I know of would be Swarovski who somehow pulls off phenomenal FOV numbers on their scopes while maintaining great eye relief.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Klamath Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 17:52
Some scopes use a wide field stop to limit the field of view to increase edge sharpness (or hide how sloppy it is).  If you see a scope like that, and they are typically less expensive to cheap ones, if the field stop is wide enough it gives the impression that you are looking through an innertube and there can be a large black expanse outside the fov of the scope.  Is that what you mean?  The exit pupil is the small disk of light you see in the center of the eye piece it you hold the optic away from your eye.
 
A good scope will have the black ring around the field, but it won't be so huge as to be distracting.  It's just where the light edge is .


Edited by Klamath - January/26/2011 at 17:54
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Post Options Post Options   Thanks (0) Thanks(0)   Quote budperm Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 20:44
Okay we're are starting to throw a few too many tachnical term around a novice might not under stand.  FOV ot Field of View, Exit Pupil, Eye relief and one that hasn't been mentioned yet but pertains to this discusion...Tunneling
 
1) FOV:  Both scopes and Binos have FOV ratings.  These are in the USA given in feet and for a given magnification specify the size or Diameter of the picture you see thru the eye piece.
 
2) Exit Pupil:  Indicates the size / diameter of the eyepeice.  As magnification goes up, Exit pupil goes down.  This is important in low light.  As light dwindles our pupils expand to let in more light.
with a small exit pupil on a scope you can't get enough light into your eye to see well in low light because your pupil will be bigger than the scopes.  reducing magnification to match or exceed your dialated pupil will maximize the amount of light from scope into your pupil and it will appear brighter.
 
3) Eye relief:   is the focal distance between your eye and the eyepiece of the scope.  usally somewhere between 2.5 and 4 inches.  short eye relief causes you to crowd the back of the scope and then you can get hit by the scope during recoil.  Called 'the kiss!'
 
4) tunneling:  The effect that reduces the FOV and has to due with magnification and your eyes alignment with the centerline of view thru the scope.   usually the higher the magnification the worse the tunneling.  Also the cheaper the scope the worse the tunneling.  It's one of the things I look for when selecting a scope for purchase.  Commonly refered to as "how easy a scope is to get behind".   usually very obvious in cheaper variable mag scopes at full mag.  You will lose part of your sight picture (view thru the scope)  If youe eye is offcenter the sight picture becomes clipped like a crescent moon.  If your eye is centered but your eye relief is off then it is like the entire diameter of you  field of view or sight picture is reduced.  Moving your eye closer or farther away from the scope eyepeice until the sight picture is the largest diameter to correct then right to left to correct for clipping.  This is refered to as 'hunting' to find the best sight picture and is a major PIA with cheaper scopes.
 
Hope this helps and if I have messed up anything I'm sure someone of the several more experienced members will help and correct me.  This is a great place to learn optics and reloading from.  Lots of highly experienced people that are very generous with their know and expertise.  I'm still learning myself. Cool
 
Sorry my spelling sucks tonight
 


Edited by budperm - January/26/2011 at 20:50
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dustyattic Quote  Post ReplyReply Direct Link To This Post Posted: January/26/2011 at 20:51
Klamath,

I know what you mean about the inner tube, I've noticed some scopes have a really fat black margin between the magnified view and the peripheral view outside the scope, while others have a barely noticeable ghost ring.

But either my eyes are lying to me, or it's an illusion, or what I'm talking about is something different. I did a few more quick tests.  I took a variable power scope and aimed it at a plain white wall.  I cranked the magnification from 3 to 9 and back, and the actual diameter of the disk I am seeing doesn't change.  Try it.. Look at a blank wall with different scopes and inform me why some of them fill your eye with a larger disk.

  I suspect it has something to do with the ocular lens design/shape which goes along with BGB's thoughts about eye relief mentioned above.  I'm interested in how the size of the disk correlates with other specs, because I haven't noticed that it does.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 03:23
Budperm, excellent explanation.
 
The only one I understood differently is "tunneling".  My understanding is that tunneling is the effect where you can see the internal side walls of the scope whilst viewing your target.
 
I further understand that seeing only part of the full exit pupil when eye not aligned with the axis of the scope is part of the eye relief function. In other words if you have generous eye relief your eye can be further off the axis and one will still have full field of view.
 
I have checked my 3,5-10 Leupold and viewed a blank wall about 35 yds away. At 10x the circle viewed is about 1/3 of the size when viewed at 3,5x.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dustyattic Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 08:23
Agreed, thank you budperm for the details.  You got your post in while I was typing a reply. I would have edited my post to acknowledge it, but I'm new and can't edit yet.  Thanks everyone for their time.

8shots..  your results confound me.  I tried a Simmons, Swift, Bushnell, and Burris, and the circle stays exactly the same size at all magnifications.  We're talking about when your head is in position, such as when shooting, not holding the scope at arms length and looking at the circle, right?  Because when I hold them at arms length and change magnification the circle does get larger and smaller. But when I am looking through it at a target, magnification changes do not change the size of the circle.

Hm.. maybe something's odd about my eyes, like I have too large pupils or something. Or would it be too small? Actually since I always see peripheral around the scope neither of those make much sense.

I lean towards the field stops explanation previously mentioned, possibly combined with my thoughts on the design of the ocular lens, and topped off with the possibility that I'm the only one seeing this. Loco  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 08:58
Sorry Dustyattic, cannot help you further on this as I do not know what round disc you are referring too. I am referring to the field of view, scope mounted on a rifle and looking at a white wall. I see a big white area of the wall on 3,5 x and I see a smaller circle of the wall on 10x.
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Klamath Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 09:43
Originally posted by Dustyattic Dustyattic wrote:

Agreed, thank you budperm for the details.  You got your post in while I was typing a reply. I would have edited my post to acknowledge it, but I'm new and can't edit yet.  Thanks everyone for their time.

8shots..  your results confound me.  I tried a Simmons, Swift, Bushnell, and Burris, and the circle stays exactly the same size at all magnifications.  We're talking about when your head is in position, such as when shooting, not holding the scope at arms length and looking at the circle, right?  Because when I hold them at arms length and change magnification the circle does get larger and smaller. But when I am looking through it at a target, magnification changes do not change the size of the circle.

Hm.. maybe something's odd about my eyes, like I have too large pupils or something. Or would it be too small? Actually since I always see peripheral around the scope neither of those make much sense.

I lean towards the field stops explanation previously mentioned, possibly combined with my thoughts on the design of the ocular lens, and topped off with the possibility that I'm the only one seeing this. Loco  


Speaking of being confounded, I really don't know what to say at this point.  You have to be talking about the exit pupil, or less likely the field of view (fov).  The laws of physics being what they are, both (Fov and exit pupil) will change with change in magnification, end of discussion.  You may be keping the scope too close to your eye.  By having the scope within the eye relief distance (or close to your eye as you state), you will not be able to see much if any change in exit pupil until you get to an exit pupil size much lower, or much higher than your dilated pupil size, and that limit may be beyond the magnification range of the scope.  Up close like that the gradual change may well be unnoticeable.  You will also be too close to measure anything anyway. Keep your eye within the eye relief specifications and you probably won't see any difference.  Even if you could, it's pretty meaningless, other than a point of knowledge and discussion topic.  It won't change how the scope works. 
 


Edited by Klamath - January/27/2011 at 10:01
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ed Connelly Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 09:52
I think he is talking about Tunnel Vision like Budperm said.  I like to pull the rifle up to my shoulder and see nothing but A Big Round View.  I don't want any Circular Borders like I am looking through a tunnel.  Or a keyhole.   
 
 
                 
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Poodleshooter1 Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 11:22
 Very critical eye relief is what causes scopes to "crescent out" I think.
I don't think actual total eye relief is necessarily the same as how critical the eye relief is.
Long eye relief is sometimes accompanied by the very critical eye relief that "crescents out" the scope view (cheap LER handgun scopes do this a lot, such as my dad's Bushnell Trophy model). However in other LER scopes, like the Nikon Omega with its 5" eye relief, you can move your head a LOT, and it's hard to get the scope to "crescent out". What you give up for this is FOV, and you get the tunnel view that feels like you're looking through a cardboard tube.

The "tunnel" effect I usually think of as being a feature of a scope with a large field stop: the view appears to be a circle at the end of a tunnel, but is not inconsistent on the sides as in the "crescent" effect above. The large field stop limits FOV and light as well, but sharpens the image just like the use of a smaller aperture does in a camera. I think Nikon makes use of larger field stops in some of their scopes. Buckmasters and Pro-staffs in particular have this as a very noticeable feature. One positive about it, is that the field stop appears to create a longer area in which a fixed focus scope is perfectly in focus at a given magnification (just like a small aperture in a camera does). For a fixed parallax scope this would be handy,as it gives better resolution over a longer range at a given power. In particular, it's useful if shooting a 100yd parallax adjusted scope at a very close range with high magnification. The narrowed aperture allows something to be in better focus at 10yds than it would be with a similar scope at the same power that has equal glass and a wider field stop. In an AO or SF scope, it's less useful since you can tune your focus (along with the parallax) anyway. I suppose in an adjustable parallax/focus scope, it would make your adjustments less critical for focus (though I don't think it would change how fine the actual parallax adjustment was).
I'm not 100% sure, but I think the other effect of this limiting field stop is to help make the eye relief less critical due to the longer focal depth, thus helping to alleviate the "crescenting out".
In my (limited) experience, it seems that I get the "crescent" effect more with cheap scopes using short eye relief and very wide FOV. The newer cheap Simmons .44Mags being an example of this.

 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dustyattic Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 12:30

Thanks guys, some of the things you've mentioned are really interesting.  I'm not really what I'd call a true novice, I'm pretty technical minded and have been shooting and tinkering with rifles and scopes for most of my 36 years.  Everything you guys have discussed makes good sense to me, easily understood.

I apologize for what seems to be my lack of ability to communicate what I'm talking about. I'll try once more but then I'll shut up before I appear to be a troll or something. 

I'll use Ed Connelly's pics above to help.  Say I have two scopes in front of me.  I pick up one and have a look.  I move my head around and front to back till I have a full, perfect sight picture as illustrated by the bottom photo. Really nice! This view could be described as a circle or disk, as I have been calling it.  My eye is "filled up" with this image, and just as your eye can move the slightest amount on your computer monitor to look at different trees, etc, my eye feels like the imagine is so wide, I can actually look around, up at the timber line, or down to the grass or back to the rock I'm aiming at within the scope's view.

Now I try the second scope.  I look through it, and see the same scene, but the "circle" is more the size of the top photo.  OK, maybe not that extreme of a difference, but the actual circle is smaller or larger from scope to scope.

The black band around the circle is not what I'm talking about.  Imagine both scopes have identical width black bands.  What I mean is looking through a scope, with my head in perfect position with the "circle" at its largest and clearest, the actual size as perceived by my eye is different from scope to scope.

I was just wondering what physical or optical property causes this.

I really think it's interesting that some say the size of this circle changes with different magnification.  For me it sure doesn't seem to with any scope I've tried.  For what it's worth, I have excellent vision.  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shenko Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 13:07
It seems like I only post here to suggest to people that they go read something that Ilya Koshkin wrote.

Got to the 'Optics Thoughts' website; Riflescope Basics article; tunnel vision section. Maybe that's what you're talking about.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 13:38
You are talking about field of view or FOV. One has a wide field of view and you can "look around"or see more, the other has a narrow field of view and therefore you see less.
The FOV definately changes as you zoom in.
 
 Field-of-view is determined by magnification and the focal lengths of the objective and eyepiece lenses. But one thing is always true: More magnification means smaller field-of-view.



Edited by 8shots - January/27/2011 at 13:40
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 13:46
Ok, again read your description. You see the same size picture, one seems more " in your face"then the other.
 
Maybe different magnification , with the same field of view, allthough the scope dials may say they are on the same magnification.
 
 


Edited by 8shots - January/27/2011 at 13:47
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bitterroot Bulls Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 13:54
I think you're talking about FOV also, Dustyattic, but it should narrow as you turn the scope up in magnification. 

If you put a yardstick up and put your scope at a distance where the yardstick fills the FOV from edge to edge, then turn up the magnification, you SHOULD see less of the yardstick (and in the middle of the yardstick).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Klamath Quote  Post ReplyReply Direct Link To This Post Posted: January/27/2011 at 14:05
Originally posted by Dustyattic Dustyattic wrote:


The black band around the circle is not what I'm talking about.  Imagine both scopes have identical width black bands.  What I mean is looking through a scope, with my head in perfect position with the "circle" at its largest and clearest, the actual size as perceived by my eye is different from scope to scope.

I was just wondering what physical or optical property causes this.

I really think it's interesting that some say the size of this circle changes with different magnification.  For me it sure doesn't seem to with any scope I've tried.  For what it's worth, I have excellent vision.  
It now seems that fov is what you are talking about.  The area of view (aka your disk of light), fov, MAY not appear to change as the magnification changes, but what WILL change is how much area shows up in the field.  Each scope has a fov defined in degrees, and different similar magnification range scopes can have different angular measurements designed into the scope.  Imagine an angle drawn out from the scope in the degree matching the fov.  FOV changes with magnification as the angle changes as the lenses in the scope move position to change power, also changing the angle.  Imagine you have a string attached to your target and think of it as pulling the target closer to you as you turn up the magnification.  As it gets closer much of the area around the target gets sliced off the view by the designed view angle.  You see less of the area around the target, but you see a bigger target.  The fov appears still to extend to fill the circular area even though it has demonstrably different properties both between scopes and between magnifications in the same scope.
 
There is also the concept of apparrent fov, which in its simplest form is the view angle in degrees, multiplied by the magnification. 
 
What we are saying changes is the disk of light defined by the exit pupil.  The problem is nobody is quite sure what your disk of light is.  If it is the fov, as I think it has to be, it is different from exiit pupil changes.  Hope this does not muddy the water any further.
 
I was going to suggest the idea of a measuring tape, but Matt beat me to it.  It may seem simple enough, but seeing is believing.


Edited by Klamath - January/27/2011 at 14:19
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