Me too. While doing some dry fires with the my teenager today, she asked what is was. So, i told her it was the Penumbra. Now, she is a whizkid at math and geometry and she looked at me like I was stupid, lol.
The Army Marksmanship unit describes the Penumbra as "the Geometric center of the Rear sight."
So, how does this help us? Well, now that we know what it is, we can use it.
If the tip of the front sight post cuts thru that little dark spot you are in perfect sight alignment. So, now we have multiple spots to check Step 1.
If you dont see the dark spot, you are not centered on the Rear Sight
I thought it was the floater in my eye ;D Sorry, couldn't resist
:o This is a family forum, lol
Quote from: RifleWoman on October 29, 2008, 06:57:18 PM
I thought it was the floater in my eye ;D Sorry, couldn't resist
Floaters, I can't resist either.
Circa, 30 years old in the history of my life, Junior year of dental school, in the lab finishing a wax up for a denture at 2:00 AM, sitting there finishing the lab work up, I saw a "gnat" flying around my face.
I was literally swatting about trying to rid this gnat, then I realized it wasn't a gnat, it was in my eyeball, a floater!!
The floater is still with me, but thankfully it's in my "south paw" (left) eye.
Quote from: U.S.Cavalryman on October 29, 2008, 06:38:23 PM
If the tip of the front sight post cuts thru that little dark spot you are in perfect sight alignment. So, now we have multiple spots to check Step 1. If you dont see the dark spot, you are not centered on the Rear Sight
Thanks US Cav, but I don't see this dark spot, at least with the M1A.
I will get a chance to shoot next week. I will look for it.
brett out.
That's weird. Never heard of it, never saw it. Now my eyes are too far gone to see it.
Quote from: U.S.Cavalryman on October 29, 2008, 06:38:23 PM
If the tip of the front sight post cuts thru that little dark spot you are in perfect sight alignment.
If you dont see the dark spot, you are not centered on the Rear Sight
Thank you VERY much. . .I was wondering if that was the case. (And wondering if I was going crazy and the only one who saw it!)
I just read this and picked up my AR to check as I'd never noticed it before... moved my head around quite a bit and still don't see it? ???
Not sure if I'm not centered, or if my mind blocks it out???
Quote from: russellmn on November 01, 2008, 02:54:26 AM
I just read this and picked up my AR to check as I'd never noticed it before... moved my head around quite a bit and still don't see it? ???
Not sure if I'm not centered, or if my mind blocks it out???
I've never seen it either and shoot Rifleman scores 2-3 times/month.
Don't worry about it.
Use a consistent cheek weld, follow the six steps, and carry on.
It is not something that will throw you off. It is just a small shady spot, just slightly darker. Some see it, some dont. If you do, you know you are not crazy.
I have been observing this dark spot for a long time. From the beginning I thought it must be due to a phenomenon called diffraction. This is caused by light rays bending slightly around objects. It is more easily seen when only one wavelength of light is present. As the light rays travel through different paths, these waves interfere with one another, producing light and dark spots. But the light we normally see is composed of multiple wavelengths. Therefore, I was rather surprised and confused, and just decided to mostly ignore it. But since this thread was started, I began to think about it more. I consulted my daughter, who has a PhD in physics. I have one too, but her main area of concentration was optics, and her research work is in that field. I have only a modest amount of training in this topic. I discovered that the "dark spot" was more visible if you sighted in on a bright lamp with a lampshade over it. I invited her to look at it, and she observed it with her eye near the butt of the stock and saw something different from what I did from a normal shooting stance, with my eye near the rear sight. We then discovered that the spot changes when you vary the distance between your eye and the sight. The farther you move away, the more dense and compact the dot becomes, and in addition, a number of straight lines pass through the smaller dot. She was familiar with these lines and referred to them as "spider webs". She indeed confirmed that it was diffraction.
I recall that when she was a child, she would ask me a question about something and I would reply that "It was physics", and then try to explain it to her. Now it is very gratifying when she can teach me something. :)
dond
Wow thank goodness for this thread! I first thought it was a piece of fuzz and tried to clean it out of the sight. When that failed I thought it might be failing eye sight or some weird disease and I was going blind. I had heard of the Zatochi the "blind swordsmen" but I wondered if it were possible to become wildman the "blind rifleman." Now I can stop worrying.
Quote from: wildman on December 09, 2008, 08:29:46 AM
Wow thank goodness for this thread! I first thought it was a piece of fuzz and tried to clean it out of the sight. When that failed I thought it might be failing eye sight or some weird disease and I was going blind. I had heard of the Zatochi the "blind swordsmen" but I wondered if it were possible to become wildman the "blind rifleman." Now I can stop worrying.
Actually, it
could be gamma radiation, or the effects thereof. Ever thought about some protection against that? **)
Gamma radiation perhaps. When are these tired eyes going to see Talon the rifleman in Ramseur again?
Quote from: dond on December 09, 2008, 12:03:56 AM
I have been observing this dark spot for a long time. From the beginning I thought it must be due to a phenomenon called diffraction. This is caused by light rays bending slightly around objects. It is more easily seen when only one wavelength of light is present. As the light rays travel through different paths, these waves interfere with one another, producing light and dark spots. But the light we normally see is composed of multiple wavelengths. Therefore, I was rather surprised and confused, and just decided to mostly ignore it. But since this thread was started, I began to think about it more. I consulted my daughter, who has a PhD in physics. I have one too, but her main area of concentration was optics, and her research work is in that field. I have only a modest amount of training in this topic. I discovered that the "dark spot" was more visible if you sighted in on a bright lamp with a lampshade over it. I invited her to look at it, and she observed it with her eye near the butt of the stock and saw something different from what I did from a normal shooting stance, with my eye near the rear sight. We then discovered that the spot changes when you vary the distance between your eye and the sight. The farther you move away, the more dense and compact the dot becomes, and in addition, a number of straight lines pass through the smaller dot. She was familiar with these lines and referred to them as "spider webs". She indeed confirmed that it was diffraction.
I recall that when she was a child, she would ask me a question about something and I would reply that "It was physics", and then try to explain it to her. Now it is very gratifying when she can teach me something. :)
dond
DonD
Thanks to you and your daughter for the Physics lesson!
I didn't know what to think when I noticed it, the VERY FIRST TIME I took a look through the NM sights on my newly bought M1A. Others didn't see it, but I saw a definite 10 o'clock to center "dark line of fuzz" in the rear sight. I will experiment with changes to position as I get cheek weld on the stock. We'll see if it disappears.
Funny thing, as I shot during our Appleseed demo at Miamisburg Club Open House last week, I saw the same effect, though much less pronounced, in the rear (Tech) sight of my 10/22.
FB
Ok..neither Paladin nor I have ever noticed this. Maybe we're too inexperienced to notice or something but we're crackin out the rifles right now to find out.
.........................................................checking.................................................
Ok..just checked. I'll be!..There is a 'putty tat'! oh..I mean a 'fuzzy spot'! Maybe it's just cat hair or dog hair- I do have a lot of them around here, after all. We'll check again when I get on the range.
Hey Fireman Bill. It wasn't as pronounced in the Tech-Sight because it is larger than the M1A NM sight. The smaller the hole, the larger the diffraction effects are.
Quote from: Talon on December 09, 2008, 08:45:07 AM
Quote from: wildman on December 09, 2008, 08:29:46 AM
Wow thank goodness for this thread! I first thought it was a piece of fuzz and tried to clean it out of the sight. When that failed I thought it might be failing eye sight or some weird disease and I was going blind. I had heard of the Zatochi the "blind swordsmen" but I wondered if it were possible to become wildman the "blind rifleman." Now I can stop worrying.
Actually, it could be gamma radiation, or the effects thereof. Ever thought about some protection against that? **)
Heh don't joke about that, Uncle made sure I had enough to last a lifetime. Not surprisingly the eye is more susceptible to ionizing radiation, even beta will cause eye damage. Sometimes I wonder if I would have been better off toting a rifle than what they had me doing at times. Good to know that spot isn't a side effect.
This answers a few questions I have and creates a yet another.
"Shoot the fuzz" is what I've heard many times. Focus on the front sight and let the target fuzz out. After finally getting NPOA and breathing down pat, the front sight was my next issue.
For the life of me I couldn't understand why I could raise or lower my view through the rear Tech Sight on my 10/22 just a smidgeon and the front sight would come in clear as a bell. Then as I centered the front post in the rear sight again it would fuzz out. Back and forth, back and forth, killing a lot of time while trying to keep the front sight in focus. After reading this post I went back to the range today and sure enough, I am picking up penumbra if I center things correctly. This darkening causes the front sight to blur a bit and it has been an ongoing problem for a couple of months now.
Now what? Stop using the center of the rear sight and dial in the sights looking above or below?
PS: Shot 217 twice today, first time as Rifleman using the AQT target at my home range - not an Appleseed. This with a 10/22, Tech Sights, and since I cannot shoot prone I have to do the bottom two rows sitting as well. Maybe a little penumbra is a good thing. ++)
jimbtv,
I have not encountered this to the extent you are describing. Try placing your eye at different distances from the rear sight. Are you turkey necking appropriately? If you can be consistent looking above or below the center fuzz, it would probably be all right, but this would probably be difficult. All I can suggest at the moment is to experiment a little and see what works best. And then try to be consistent.
I've got a new M1A. Slung it up having recently learned how to use a sling at an appleseed. Sure enough, I'm seeing this fuzz. I don't have a spot, but rather a black fuzz line. I had read this thread before seeing it, so knew what it was right away. I'll see if I can use it, looking for a spot.
I use it to identify when i am perfectly centered on the rear sight. Then I get the front site in the center of that. Kind've a reverse Red dot scope, lol. I shoot fairly well but any little trick I can find helps.