Eliminating Parallax

[Bart B.]

Parallax does not require optical lenses. It comes from an old Greek word
parallaxis. Look it up.

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

 

[JohnKSa]

Visual parallax does not require optical lenses.

I didn't say it did.

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

Agreed. Agreed since the very beginning of the thread.

 

[Bart B.]

Things are not different with aperture nor open sights. A small aperture or notch does not act like a lens, light going through it doesn't change medium like glass to air lens curved surfaces do to change its direction. It's all air.

 

[JohnKSa]

According to the paper you quoted, they are quite different with aperture sights.

According to what I can see with my own eyes, they are quite different with open sights, but for a different reason.

A small aperture or notch does not act like a lens...

Ever hear about a pinhole camera?

https://www.quora.com/How-can-a-pinhole-act-as-a-lens

https://www.howtogeek.com/161794/how-to-take-pinhole-photos-with-a-digital-camera/

"How can you have a lens with no glass? With a traditional glass lens, the optical elements are shaped and polished so that the lens is able to collect light over a wide area and pass that light through the barrel of the lens onto the focal plane of the camera body (where the film or sensor is located), while preserving the image without distortion. With a pinhole “lens” the same effect is achieved, but through different means. Because the opening, or aperture, or the pinhole lens is so very tiny it allows only a very small amount of light to pass through it. The rays of light and the tiny amount that passes through the pinhole opening stay almost perfectly parallel with each other (a feat the glass-based lens needs carefully machined and polished elements to achieve)."​

https://electronics.howstuffworks.com/question131.htm

"The pinhole in a pinhole camera acts as the lens. The pinhole forces every point emitting light in the scene to form a small point on the film, so the image is crisp. The reason a normal camera uses a lens rather than a pinhole is because the lens creates a much larger hole through which light can make it onto the film, meaning the film can be exposed faster."​

I agree that a notch is something else entirely from an aperture.

We're wandering farther and farther away from your initial questions and whatever purpose you had in asking them. This is still an interesting discussion, but I can't help thinking that this isn't what you intended.

 

[zukiphile]

Things are not different with aperture nor open sights. A small aperture or notch does not act like a lens, light going through it doesn't change medium like glass to air lens curved surfaces do to change its direction. It's all air.

Emphasis added.

Your linked article aptly explains the difference. A smaller aperture produces a smaller image than the eye's "aperture" and masks some of the shooter's alignment error. An open sight doesn't.

I shoot pistol with an open sight, and an iron sight rifle. I can assure you that the aperture is doing something the open sight isn't.

 

[Bart B.]

A smaller aperture produces a smaller field of view than the eye's "aperture" and masks some of the shooter's view further from point of aim. Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused. No alignment error is masked.

Pin hole cameras do not act like a lens, they don't bend and focus light rays. They're identical to aperture rear sights as far as rays of light going through them. A ray of light entering a tiny or huge hole exits at the same angle it entered.

 

[JohnKSa]

Communication requires common language. If you're going to make up your own definitions for things and insist upon them in the face of evidence to the contrary, it's impossible to communicate.

https://en.wikipedia.org/wiki/Pinhole_occluder

"A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light,"

https://en.wikipedia.org/wiki/Pinhole_camera

"In the region of near-field diffraction (or Fresnel diffraction), the pinhole focuses the light slightly, and the resolution limit is minimized when the focal length f (the distance between the pinhole and the film plane) is given by f = s2/λ. At this focal length, the pinhole focuses the light slightly, and the resolution limit is about 2/3 of the radius of the pinhole. The pinhole, in this case, is equivalent to a Fresnel zone plate with a single zone. The value s2/λ is in a sense the natural focal length of the pinhole."​

http://hilaroad.com/camp/projects/pinhole.html

"A tiny hole (less then 1 mm), focuses light passing through it, much the same way a lens does."​

https://www.flickr.com/groups/84458270@N00/discuss/72157604778403047/

"Pinholes, like (uncorrected) lenses will only focus one wavelength "perfectly"."​

https://www.asu.edu/courses/phs208/patternsbb/PiN/rdg/camera/camera.shtml

"But the aperture itself can function as a lens."​

https://www.exploratorium.edu/tinkering/blog/2017/06/20/pinhole-cameras-with-modesto-tamez

"To start off our exploration, Modesto demonstrated how a pinhole can focus light without a lens. "​

But you know, I kind of think you were already completely aware of this property of apertures. Just a guess on my part...

Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused

No alignment error is masked.

The paper you linked to states that an aperture sight system masks eye alignment errors.

Bart, where were you going with the questions you posed at the beginning of the thread??? Can we reset back to the beginning of the thread, start over with common terminology and accepted definitions and maybe get this back on track?

 

[zukiphile]

A smaller aperture produces a smaller field of view than the eye's "aperture" and masks some of the shooter's view further from point of aim. Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused. No alignment error is masked.

The underlined language is correct but makes a different point. An alignment error is masked where it is concealed from a viewer because the point of perspective is fixed despite movement of the viewer's eye. The bold assertion is incorrect. In the article, that point is explained at page 6.

Now, if we move our eye from side to side a little bit, our first thought is that the point of perspective would change. But since the point of perspective is at the center of the sight aperture, and that is fixed, the point of perspective does not move.

In pages 7 and 8, the authors explain the qualities of a small aperture sight that are not like an open sight.

 

[Bart B.]

Maybe someone can explain why my shots aimed with aperture front and rear sights having a 29 to 38 inch radius never pointed the barrel such that bullets went to call (for rifle-ammo accuracy) at ranges from 50 to 1000 yards unless their centers were all on the same visual axis from eye to bullseye target.

I'm not the only one who would like to know.

 

[zukiphile]

Maybe someone can explain why my shots aimed with aperture front and rear sights having a 29 to 38 inch radius never pointed the barrel such that bullets went to call (for rifle-ammo accuracy) at ranges from 50 to 1000 yards unless their centers were all on the same visual axis from eye to bullseye target.

Bart, could you re-phrase that? I'm guessing there is some idiomatic material here, because I'm gleaning that you shoot rimfire out to 1000 yards, and the bullets never went to call ( I don't know what "went to call" means) unless their (I don't know the antecedent for "their") unless their centers were all on the same visual axis.

The excerpt I quoted above explains why the center of the eye need not be on the same axis as the aperture front sight and POA if the aperture is small enough.

The concept of a single axis involves a specific point on the eye. At page 5, the article addresses that idea.

This at first seems a little over-simplistic. After all, the eye doesn’t just regard the world through the center of the entrance pupil, but rather through all of it. So shouldn’t we consider that the eye has many “vantage points”, one for every imaginable location within the entrance pupil?

 

[Bart B.]

When shot from most stable positions allowed......

Rimfire from 50 to 100 yards, centerfire from 200 to 1000.

"Went to call." means bullets strike the target where the sights were aligned to when the round fired. A tolerance of half the system test group size is considered. If your stuff tests no worse than half MOA at target range, shots should strike within 1/4 MOA of call; atmospheric conditions allowing, naturally. A good marksman can hold point of aim inside a half MOA.

Everyone whose shot 20 record shots slung up prone shooting rimfire ammo at 50 yards all inside 1 MOA scoring Xes with metallic sights all say target, front and rear sight centers must be on one axis (no parallax ((or misalignment))) with either one) to do that.

Same for centerfire from 200 to 1000 yards with at least 2/3rds of 15 or 20 with a few deep in the 10 ring due to environment conditions

 

[JohnKSa]

Maybe someone can explain why my shots aimed with aperture front and rear sights having a 29 to 38 inch radius never pointed the barrel such that bullets went to call (for rifle-ammo accuracy) at ranges from 50 to 1000 yards unless their centers were all on the same visual axis from eye to bullseye target.

Because properly aligning iron sights involves putting the front sight/rear sight/target in a line and the only way to see to do that is if your eye is also in the same line.

That said, the article you brought up asserts (and backs up the assertion with real-world testing and scientific explanations) that well-designed aperture sights are forgiving of minor misalignment of the rear sight and the eye.

 

[Bart B.]

That said, the article you brought up asserts (and backs up the assertion with real-world testing and scientific explanations) that well-designed aperture sights are forgiving of minor misalignment of the rear sight and the eye.

Not when the test groups are greater than MOA without tests with a scope to establish what the rifle can do with the ammo and no plots of call versus shot hole to show errors caused by parallax errors.

Don't forget about the other axis whose angle and direction from the two sights axis doesn't change.

 

[JohnKSa]

I'm ok with just the first part of my explanation, but since you brought up the article, I thought it made sense to at least give its contents a nod.

So:

"Because properly aligning iron sights involves putting the front sight/rear sight/target in a line and the only way to see to do that is if your eye is also in the same line."