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Discussion Starter · #1 ·
Some time ago the "virtual" aperture fuzz (as I call it) was discussed - maybe several times. This is the appearance of some lint-like blockage in the aperture of the rear sight when using irons. There was an explanation of why this is so for some shooter's eyes. Could someone (Art?) direct me to that discussion? Then maybe I can ask my question - if it still remains.
 

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Discussion Starter · #2 ·
Okay, so I've spent some time searching old threads that had posts from "shootingsight". Perfect. Found everything I was trying to remember ... and more.

Anyone else who may want to look back at this subject, do the search I suggest and go back at least as far as:

http://m14forum.com/m14/105359-nm-sight-question.html

I think I now know what I want to get to help.

Cheers!
 

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Eye Master
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Actually, there is more to it.

Some people get this 'fuzzball' in their aperture, and there have been lots of explanations, and I'm convinced they are all wrong. I have heard people refer to it as penumbra, and this is just plain wrong if you look up the definition of the term. FOr a long time, I attributed it to diffractive error, but that is also wrong, because for one, when you run the math on diffractive error, it should not happen until MUCH smaller than 0.040", and finally, if it were diffractive error, everyone would see it, not just some people.

Of course, it does not matter much, because even if the hypothesis I'm working up is the correct one, neither my explanation nor the wrong ones gives you an answer to eliminate it. OK, maybe I have an answer, but I have not tried it yet, so you can be my first subject.

The answer is BOKEH. It is a Japanese word, meaning blur, and photographers use it to describe the blur line around an object that is out of focus.

So in the simplest sense, if I have a black field, and a white field, and there is a sharp demarkation between them, they are in focus, and if I plot out the brightness that is hitting the pixels in my retina, they will be zero (black), and then all of the sudden, from one pixel to the next, you go to 100% (white). A step function.

Now, when you de-focus the image, and create blur, the question arises about what that blur looks like. In the simplest description, a plot could be a linear progression from black to white. Camera lens companies play with lens designs, including the shape of the aperture, to try and achieve a sinusoidal or Gaussian blur, so the plot starts out changing slowly, then changes rapidly, then goes back to a gradual change. This is considered more pleasing to the human eye.

I have recently noticed that when I look at a vertical edge that is blurry, I see black, then there is a narrow line of white, then a narrow line of black, then it finally goes to white. In other words, next to the black surface is a thin line of black, offset from the real edge. This might be caused by the shape of my cornea, or pupil, or the spacing of pixels on my retina, but I don't know yet.

I need to dig into human eye anatomy and my old photography books to better understand what causes bokeh to be different shapes, but bottom line is that when I apply this notion of a black line that is offset from the real edge, and apply it to looking through an aperture, I will see a black ring, offset from the aperture edge.

Now, if I shrink the aperture , such that the radius of the aperture corresponds to the offset of this black line I am seeing, the black ring will pile up into the center of the aperture and form a dark spot. This is what some shooters are seeing.

So I believe it is eye dependent.

But here is my solution thought: if it gets really bad as the aperture radius approaches the offset of the black line, could you fix it by going smaller? At some point, if the radius of the aperture is smaller than the offset of this line, the fuzz will start to dissipate again.

Just a thought. This problem has been bugging me for 5 years, and I think I'm on tothe right track, but I need to engage some optics experts who know way more than I do to try and solve it.
 

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Discussion Starter · #4 ·
I would say that I seem to find the effect diminished in brighter light conditions.

What you say sounds perfectly reasonable and why I only first saw it when looking through the aperture for the sight picture. Though now I've come to notice that I see this "fuzz" when looking through any small aperture - even one I create between my thumb and forefinger when I make the opening small enough.

As an aside, I was in for an eye exam yesterday and asked the Doc about "fuzz" and didn't get much that sounded helpful. Though, I did leave with a contact lens for my right eye that is supposed to address astigmatism. No astigmatism in the left eye and otherwise my contact lens prescription didn't change.

So I am considering ordering shootingsight's +0.5 diopter lens and furnishing my prescription so the astigmatism correction could be applied for use in the NM hooded aperture. From what I've read this could be an improvement over the usual BJones lens that I have. (This would be in addition to my contact lens correction. Yes? I would use it with my astigmatism corrected contact lens? Or go back to the uncorrected contact lens?)
 

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Hi ShootingSight and others

My problem with the Tunnel of Fuzz brought me to this thread.

Has there been any update to your knowledge on dealing with
this problem ?

Thanks ! Chris




Actually, there is more to it.

Some people get this 'fuzzball' in their aperture, and there have been lots of explanations, and I'm convinced they are all wrong. I have heard people refer to it as penumbra, and this is just plain wrong if you look up the definition of the term. FOr a long time, I attributed it to diffractive error, but that is also wrong, because for one, when you run the math on diffractive error, it should not happen until MUCH smaller than 0.040", and finally, if it were diffractive error, everyone would see it, not just some people.

Of course, it does not matter much, because even if the hypothesis I'm working up is the correct one, neither my explanation nor the wrong ones gives you an answer to eliminate it. OK, maybe I have an answer, but I have not tried it yet, so you can be my first subject.

The answer is BOKEH. It is a Japanese word, meaning blur, and photographers use it to describe the blur line around an object that is out of focus.

So in the simplest sense, if I have a black field, and a white field, and there is a sharp demarkation between them, they are in focus, and if I plot out the brightness that is hitting the pixels in my retina, they will be zero (black), and then all of the sudden, from one pixel to the next, you go to 100% (white). A step function.

Now, when you de-focus the image, and create blur, the question arises about what that blur looks like. In the simplest description, a plot could be a linear progression from black to white. Camera lens companies play with lens designs, including the shape of the aperture, to try and achieve a sinusoidal or Gaussian blur, so the plot starts out changing slowly, then changes rapidly, then goes back to a gradual change. This is considered more pleasing to the human eye.

I have recently noticed that when I look at a vertical edge that is blurry, I see black, then there is a narrow line of white, then a narrow line of black, then it finally goes to white. In other words, next to the black surface is a thin line of black, offset from the real edge. This might be caused by the shape of my cornea, or pupil, or the spacing of pixels on my retina, but I don't know yet.

I need to dig into human eye anatomy and my old photography books to better understand what causes bokeh to be different shapes, but bottom line is that when I apply this notion of a black line that is offset from the real edge, and apply it to looking through an aperture, I will see a black ring, offset from the aperture edge.

Now, if I shrink the aperture , such that the radius of the aperture corresponds to the offset of this black line I am seeing, the black ring will pile up into the center of the aperture and form a dark spot. This is what some shooters are seeing.

So I believe it is eye dependent.

But here is my solution thought: if it gets really bad as the aperture radius approaches the offset of the black line, could you fix it by going smaller? At some point, if the radius of the aperture is smaller than the offset of this line, the fuzz will start to dissipate again.

Just a thought. This problem has been bugging me for 5 years, and I think I'm on tothe right track, but I need to engage some optics experts who know way more than I do to try and solve it.
 

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Eye Master
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There is update, and I am convinced my prior post was incorrect.

My current belief is that some people have micro defects in the lens or the cornea. These can develop over time. These defects cast a shadow on your retina. When light is coming in from the entire pupil, the shadow is vague and blurry enough that you cannot see it. However as the light source coming in to your eye goes from a 1/8" opening (the size of your pupil), and becomes ever smaller (ie looking through an aperture), the sharpness of the shadow edges become more clear, and your retina can actually see the shadow of these defects.

You see a similar phenomena in a pool lit by sunlight. The sun is pretty close to a point source of light, and when the surface of the water has even a slight ripple to it, it creates light/dark spots on the bottom of the pool.

This still does not help you solve it - other than by moving to a larger aperture.
 

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I have recently noticed that when I look at a vertical edge that is blurry, I see black, then there is a narrow line of white, then a narrow line of black, then it finally goes to white. In other words, next to the black surface is a thin line of black, offset from the real edge. This might be caused by the shape of my cornea, or pupil, or the spacing of pixels on my retina, but I don't know yet.
It has been more than 20 years since I've been in school, though I remember a class in human perception that described an illusion similar to what you're describing, and it had to do with neural processing between the eye and the brain proper, whatever you call that...

But here is my solution thought: if it gets really bad as the aperture radius approaches the offset of the black line, could you fix it by going smaller? At some point, if the radius of the aperture is smaller than the offset of this line, the fuzz will start to dissipate again.
I know that with cameras, as you shrink the aperture, you increase depth of field, so that more is in focus, but as some point you start losing resolution as the diffraction effects become larger than the resolution of the sensor. The lower the resolution of the sensor, the more you can shrink the aperture before noticing the impact to sharpness, because you get an artificial sharpness through the structure of the pixel, and you get more of that quick step the lower the resolution of the sensor...

Not really helping here, but an interesting topic.

Also, in higher light, your eye aperture will 'stop down' and close, so that you will see less of the optical defects in your own eye. Less of the eye is used for any given portion of image on the retina, so it is less critical that it actually functions cohesively.
 

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Eye Master
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I think the analogy is if you illuminate an object with a large light source, like a flourescent light, the shadow is very indistinct. However if you illuminate something with a very small pinpoint light source, you will cast a sharp shadow.

When you have a defect on the cornea, allowing light into your eye from your pupil is a large light source. When you look through a 0.040 aperture, that is a small light source.
 
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