August 11, 2019, 08:49 AM | #1 |
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Eliminating Parallax
Is parallax eliminated the same way with both metallic and optical sights?
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August 11, 2019, 10:12 AM | #2 |
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Is parallax eliminated by iron sights, or is error just reduced by the size of the aperture?
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August 11, 2019, 12:09 PM | #3 |
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I believe parallax is an issue unique to optics, and does not occur with open or aperature sights that utilize no optical elements.
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August 11, 2019, 12:39 PM | #4 | |
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Does a barrel aimed with metallic sights always point to the same place on target regardless of how they may appear relative to each other and the target? Last edited by Bart B.; August 11, 2019 at 01:38 PM. |
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August 11, 2019, 03:22 PM | #5 | |
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How are you defining parallax? I don't see how you could have parallax in metallic sights as the requirements for aiming with metallic sights pretty much rules out parallax by forcing the shooter's eye into proper position.
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August 11, 2019, 04:21 PM | #6 |
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Parallax with metallic sights exists when front and/or rear sight center is not on the line of sight between eye and target center.
With a good zero for target range, when front and rear sight centers are on the line of sight (LOS) from eye center to target center, shots so fired will strike the target center. If front sight center is to the right of aperture center but centered on target upon firing, shot will go right because the line of fire (LOF) points right of LOS. If rear sight center is to the right of front sight centered on target when fired, shot will go left because the LOF points left of LOS. Shooter has to conciously correct front and rear sight alignmen to the LOS from eye to target. Last edited by Bart B.; August 11, 2019 at 05:06 PM. |
August 11, 2019, 04:32 PM | #7 | |
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Another shooter may hold the rifle differently and a rifle zeroed for me may not impact in the same spot as someone else. And I see this as more of an issue with iron sights than optics.
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August 11, 2019, 04:53 PM | #8 |
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August 11, 2019, 04:55 PM | #9 |
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It's equal both ways. I've observed this a few times shooting 4 man team matches with the same rifle and ammo.
Last edited by Bart B.; August 11, 2019 at 05:02 PM. |
August 11, 2019, 05:07 PM | #10 | |
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Parallax exists when the sight(s) appear to be properly aligned with the target but aren't because the shooter's eye is not properly aligned with the sight(s). That can't really happen with metallic sights.
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Last edited by JohnKSa; August 11, 2019 at 05:24 PM. Reason: Corrected wording. |
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August 11, 2019, 05:43 PM | #11 | |
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Also with a collimator and live fire exercises. |
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August 11, 2019, 07:00 PM | #12 | |
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I know I have a parallax problem in an optic when the optic is zeroed and the rifle stationary as I look through the optic and move my head, but not the rifle or the sights. Parallax will make the crosshairs appear to move on the target even though I know the point of aim can't actually be changing. If I do the same with an iron sight rifle (move my head while the rifle is stationary), the front post and target move off center, so I no longer have what appears to be an aligned sight. That's not a parallax error because it isn't an error, but the iron sights doing what they are designed to do -- tell you when the back and front are or are not aligned to a spot on the target.
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August 11, 2019, 07:17 PM | #13 |
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post #5 and #10.
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August 11, 2019, 07:28 PM | #14 | |
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The only way to eliminate parallax is to put the muzzle against the target.
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August 11, 2019, 08:03 PM | #15 |
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Parallax in a rifle scope exists when the target image is not in the same plane as the reticle. It can be corrected by refocusing the objective (front) lens so that the target image is corrected to the same plane as the reticle, such as on adjustable objective rifle scopes. Focusing the eyepiece does not correct for parallax, it corrects for refractive errors in the eye.
Since there is no target image produced by an open sight system, there is no parallax. A diopter lens in an aperture sight is used to correct refractive errors in the eye.
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August 11, 2019, 08:08 PM | #16 | |
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We first must agree on what parallax is defined as by some standard; perhaps a dictionary? https://en.wikipedia.org/wiki/Parallax Last edited by Bart B.; August 11, 2019 at 09:16 PM. |
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August 11, 2019, 09:57 PM | #17 | |||
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However, that can't happen with metallic sights because there are TWO components to the sights, not just a single aiming reticle. The eye, the front and rear sight and the target all must be in a line when the rifle is aimed. As soon as the eye moves out of line with the sights, the sights are no longer lined up with each other and so it's obvious that there's a problem. In a system with true parallax, the reticle/aiming device does not show an obvious problem when the eye moves off axis--it's just that the bullet won't hit where the reticle says it will. Quote:
In other words, if we're talking about an apparent movement of the "point of aim" on the target due to the motion of the eye, it can't happen with a metallic sight setup because once the eye moves off axis, there is no longer any definable "point of aim". There's just a multiply misaligned system. Moving the eye off axis in an optical system that is susceptible to parallax creates a parallax situation where the apparent aiming point is not the same as the actual aiming point. Moving the eye off axis in a metallic sight system effectively "destroys" the aiming point so there is no longer any apparent aiming point at all.
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August 12, 2019, 05:47 AM | #18 | |
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Right? |
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August 12, 2019, 06:51 AM | #19 | |
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While parallax can be observed when any two objects are at different distances, misalignment of iron sights isn't the same phenomenon as parallax evident in an optic at a given distance. The ideal on an optic is to have everything focused on the same plane. Since that can't ever happen on iron sights, parallax can't be eliminated the same way. On one parallax is a simple alignment problem; on the other its a focal plane issue. One can remedy or reduce parallax error in an optic with the use of an aperture that demand better alignment, but since greater flexibility and ease of use are part of the advantage of an optic, that's not a very popular remedy.
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August 12, 2019, 09:04 AM | #20 | |
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I've intentionally misaligned aperture sights to see how far and direction bullets strike from point of aim. I used to think otherwise until my small arms Marksmanship Instructor showed me how to prove otherwise. Easily done if you can shoot your iron sighted rifle sub MOA for 20 shots. Remember the back end of the barrel moves left if the front sight appears right of aperture center. Both the LOS and LOF pivot on the front sight. That makes the bore point to the right from point of aim on target. Bullet will go that way from point of aim when fired. Last edited by Bart B.; August 12, 2019 at 09:16 AM. |
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August 12, 2019, 09:23 AM | #21 | |
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The ideal for parallax correction in an optic involves the eye at one end and a single focal plane on which that eye sees the target and crosshair; that can provide a cone rather than a single axis at which the reticle will accurately represent the point of impact. Above, you've described a lack of parallax correction. The reason you can have that specific axis is that the focus of target and crosshairs cross at different distances. To address your original question, fixing alignment by getting everything on one axis can work on an optic too. I've gotten good results from scopes without parallax correction at shorter distances just using a stock that fits well enough to reduce head movement. It isn't perfect, but it gets rid of the sort of gross errors one can see at shorter distances.
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August 12, 2019, 12:34 PM | #22 |
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Why is that knob opposite a scope's windage knob commonly called a "parallax" adjustment when all it does is focus the upside down first image plane on the reticle in the second image plane right side up?
When all scope's front lens cell was twisted to focus the target image upside down on the first focal plane, it was called "range" or "target" focus. Most knew the erector tube lenses refocused and inverted that image on the reticle in the second focal plane. Too bad its well understood name never made it to all scopes with that third knob. |
August 13, 2019, 01:06 AM | #23 | ||
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None of that has anything to do with parallax using the definition you chose and linked to. Quote:
When you're talking about aiming with metallic sights, it involves aligning the sights and the eye. With the sights and the eye aligned, the sights create an aim point on the target. When the eye is off axis, there is no aim point because for there to be an aim point, the sights and the eye have to be aligned. I think what you're trying to say is that because the bullet will hit somewhere even with the sights misaligned that there must be an aim point. That's not true. If you pull the trigger without aiming at all, the bullet still hits somewhere--but there was no aim point. Or maybe what you're saying is that because it is possible to calculate where the bullet will hit, or predict it with some other methods, even when the sights are misaligned, that there must be an aim point. But that's not true. If the metallic sights are not aligned with each other and with the eye, then there's no aim point. I suppose if there are SMALL misalignments, then one could argue that there is still an aim point but that it won't correspond with the impact point. The problem is that it's not possible to say if that situation is due to the eye being off axis from the sights or the sights simply being misaligned. In other words, there's still no way to definitively call that parallax because it's impossible to know if the problem is the eye being out of the axis with the sights very slightly, or if the eye is in the right place but the sights are misaligned slightly. Maybe it would be easier to start out with an answer to this question that we can all agree on. If metallic sights are not aligned (let's say that the front sight isn't in the notch or aperture or maybe it is even completely obscured by the rear sight) what is the aim point?
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August 13, 2019, 06:31 AM | #24 | |
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"Aim point," to me, is the place on target the place on target the front sight is aligned to in the sight picture. It's the far end of the straight line of sight from the aiming eye through the rear sight to the front sight then to some place on target.
Does that make sense? If not, we need to establish a set of names, terms and conventions. From SAAMI's glossary: Quote:
Last edited by Bart B.; August 13, 2019 at 07:36 AM. |
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August 13, 2019, 07:18 AM | #25 |
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Parallax is the apparent shift in location of one object relative to another object at a different distance by a change in the observer's position. With firearms, parallax can exist with a single sight (such as a shotgun bead), but does not exist with metallic sights consisting of two or more elements. Parallax requires an observer [eye], an single middle object, and a distant object. A pair of metallic sights are aligned in only one eye (observer) position, and movement of the eye position misaligns the sights. So the various metallic sight senarios stated here are examples of sight misalignment as opposed to parallax.
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