How the heck does a red dot scope work?

[jamz]

I'm not that bright, and I picked up a red dot scope the other day (new toy syndrome). I don't know how these things are supposed to work, but when I turned it on and looked through, I was expecting a red dot to be permanently centered in the glass. What I didn't expect is that the dot moves all around when you move your head. If the scope viewing area was small, like with a peep sight, centering it would not be a problem, but this sight's viewing area is pretty big.

My question is, how are you supposed to aim with this thing? What keeps the dot from moving when you move your head as opposed to the barrell?

Thanks for any advice.

-James

 

[whm1974]

I shot a couple of .22 pistols at the range with red dots on them. Right now I hate those things, just give me plain sights or a scope anyday.

-Bill

 

[RJ357]

If the dot were fixed in the center, then it would be a problem. If you imagine it fixed, you can see that the dot would move in relation to the target even though the gun (and sight) are not moving.
The reason the dot moves as you move your head is that the dot is a virtual image. It appears as if it were located at the target and not inside the sight tube. Ideally, the dot would always appear fixed on the target regardless of the position of your head (assuming the gun and sight don't move). In reality, this is only true at a certain distance. At greater and lesser distances, the dot will move off target as you move your head. This is parallax error, or simply parallax.

Hope I didn't make it more confusing.

 

[R.H. Lee]

The red dot is a projected image (from an led I think) that bounces around like crazy. Usually a red dot scope has no magnification. I can't think of a use for them and consider them a gimmick, but then I've never owned one.

 

[dukeofurl]

Apparently most folks here who have never shot an aimpoint or any other gun with "red dot" optics have never seen some bullseye and USPSA Open.

The dot is supposed to move when you move your head. The gun stays in the same place and your head moves, so when you see the dot moving around. Imagine that you're shouldering an AR15, you hold the gun tight to your shoulder and move your head around and the front sight moves around. Same concept. The aimpoint (we're talking about the red dot here, not the brand) is where the gun is sighted in to shoot. You adjust the dot appropriately when sighting in and these types of optics deliver extrordinary speed when shooting almost anything - bowling pins, reactive steel, etc.

The point to it is speed of target acqusition.

Just dont shoot your AR15 homeboy style with an Aimpoint (the brand of optic) at 100 yards and expect to hit much.

 

[dukeofurl]

I think several models come in magnification. I know of one USPSA 3gun shooter who has 2 red dots mounted on his AR, one is magnified for long range targets, the other is mounted at a 45 degree angle to the top of the gun and is used for running and gunning in close range targets whether on the run or stationary.

 

[Werewolf]

I bought one for my AR-15. Mounted it on there thinking it would be good for quick acquisition. Kinda - but I could never hit anything with it mounted and when I traded my AR-15 for an M1 Garand I left it on the AR. Got about an extra $100 in trade too because it was on there ($39 Red Dot). Since I got just a measely $50 less in trade value than I paid for the AR and Red Dot I didn't feel bad at all.

FWIW I believe based on my experience that a red dot is an excellent accessory for a pistol or revolver that will be shot at ranges of 25 yards or less. Other than that - worthless.

Then my opinion is worth exactly what you paid for it (divide your monthly ISP cost by the time it took to read this) probably about 2 Cents!

 

[Arc Angel]

I've got one of Aimpoint's Comp II red dot sights that I use on several different pistols. That dot is supposed to move as other posters have explained. One of the first things you have to do is read the instruction manual that comes with the sight. Then you have to take the caps off the adjustment knobs and sight the red dot in for the particular gun and approximate distance that you intend to shoot at. (My suggestion would be to start close, say 15 yards, and progress outward from there.)

Personally I like a smaller dot; (3 MOA) and I use my Aimpoint Comp exactly the same way I use an optical sight. I don't mean to criticize; but, if you're having trouble with a red dot sight, I strongly suspect that you've, also, never learned how to use an optical sight correctly - either. The functions as well as the problems are nearly identical.

When I, first, started using my Aimpoint Comp I, 'muffed' a group of close targets during an IPSC style shoot. I was holding dead center; and I should have hit every one of them; instead I missed almost an entire row because I ignored the same, 'close optical distortion' that happens whenever you try to use an optical scope too close in. I realized the mistake on the last two targets and dropped the dot to the bottom of the target in order to hit dead center. Red dot sights take a little getting used to; and they are worthless in the dark; but under normal light conditions they are unquestionably faster and easier to use than the naked eye – so much so that, sometimes, I almost feel like I’m cheating whenever I use one. Still, my old eyes can use all the help they can get!

 

[jamz]

I don't mean to criticize; but, if you're having trouble with a red dot sight, I strongly suspect that you've, also, never learned how to use an optical sight correctly - either. The functions as well as the problems are nearly identical.

This is entirely true. I'm self taught with optics. I have no real clue what I'm doing. However, with a normal scope, with crosshairs, it's centered and doesn't move. You sight it in, and when the rounds strike where you have the crosshairs, (at a given range) it's sighted in.

So take that to the red-dot, and I get confused- it's as if the crosshairs were moving all over the place on the scope. I am lost!

So, are you guys saying that the red dot just needs to be used with a huge amout of eye relief, like 6 inches or more?

-James

 

[Zak Smith]

When you're sighted in on your rifle with a regular scope and you wiggle your head side to side or up and down and the crosshairs "move" on target, but you haven't changed where the gun is pointing- that's parallax. With a scope, you want a consistent cheek weld to make sure there is either no parallax error (ie, it's centered) or it's as least consistent shot to shot.

A well-made red dot, like the Aimpoint Comp M2, is parallax free, which means that within some limitations, as long as the dot is "on" the target, the bullets will strike there. This is to allow varied eye / ocular lens positions and not screw up your point of impact.

-z

 

[Arc Angel]

Here’s some light reading for you; it should help clear things up:

http://www.aimpoint.com/o.o.i.s/1

http://articles.findarticles.com/p/articles/mi_m0BQY/is_5_47/ai_72407708

http://www.army-technology.com/contractors/machine_guns/aimpoint/

And, even though it references sighting in an Aimpoint on a crossbow, the following is as good an explanation as I’ve come across on the internet:

http://www.barnettcrossbows.com/opmanpistols.htm#ELECTRONIC DOT AIMPOINT SCOPE INSTRUCTIONS

Good luck to you!

PS: If you're confused by these comments about, 'parallax error'. Here's an explanation of what's going on:

http://home.sprynet.com/~frfrog2/miscelll.htm#parallax

 

[bobs1066]

Ages ago, I had one of the old Weaver QuickPoint sights on a shotgun. That thing was death on 'possums & 'dillers. Didn't take much ambient light to make the red dot show. At least for a shotgun, I've nothing but good to report.

 

[Zak Smith]

To add,

A 1x magnification (ie, none) red-dot such as the Aimpoint M2 has infinite eye relief. In other words, you have it 1" away from your eye, or 20" away, and it will work just as well.

With an Aimpoint M2, the preferred method of shooting is to keep both eyes open and place the dot at the desired POA. The closer to your eyes the scope is, the more of your field of view will be the black tube which surrounds the optics. The closer from your eye, less of your field of view is blocked by the housing. On the AR15 platform, most people put their dots either at the far end of the flat-top receiver, just before the barrel, or about 1.5" forward of there, on some sort of cantilevered mount.

-z

 

[Zak Smith]

One more neat thing about a red-dot sight, if it is parallax free, is that you can shoot with the front lens blocked (!!) - seriously. If you shoot with both eyes open, your strong-side eye does not need to look "through" the scope. With the front lens blocked, the lit dot will still be visible and your brain will super-impose it on your target. This was originally done in the Armson OEG (occluded eye gunsight) and is the basis for the BAC (Bindon aiming concept) in Trijicon ACOGs.

 

[RJ357]

jamz -

Place the sight on a solid surface so it doesn't move (not holding it). Look through the sight at something distant, about the same distance as a target would be. Now you should notice that as you move your head, the dot will move in relation to the tube, but will not move in relation to the target.
Also notice that as you move your head, the target also moves in relation to the sight tube. Both target and dot move together.
If the dot moves in relation to the target (parallax), then the parallax has been zeroed out for a different distance. If the parallax is not adjustable, then it has been preset by the manufacturer for some typical target distance.

 

[RJ357]

Think of the red dot sight as a scope with X1 magnification and a red dot instead of crosshairs.
The real difference is in the size of the exit pupil. Light comes from the scope in a thin column, as if you were looking through a tiny hole. The size of this "hole" is the exit pupil and in a scope it is only a few millimeters. That is why you will lose the image with only slight movements of your head. In a red dot sight, the exit pupil is much larger and allows a wide range of movement without losing the image.

Another difference is that the parallax is adjusted out for a closer distance in the red dot. When used at the zero parallax distance, the dot will not move on the target when you move your head. At closer or farther distances the parallax increases. The farther (or nearer) the target, the worse it gets.

The same effect that you are seeing in the red dot sight also exists in a scope. You just don't notice it because the range of movement of your head with a scope is severely limited.

 

[Standing Wolf]

It took me a couple trips to the range to get used to my first red dot sight. As my eyes age, I'm becoming more and more dependent upon them.

 

[Harry Tuttle]

just remember

ya get what ya pay for...

those 29 dollar red dots are not 250 dollar Aimpoints
but they do go up to 11

 

[P95Carry]

Jamz .. I didn't look at Arc Angels links - and I am sure they tell all.

But - IMO - easiest way to imagine the ''guts'' of a red dot ...... is to imagine a LED laser or just Hi-Intensity red LED ... projecting from below onto a half silvered mirror. That mirror is adjustable for windage and elevation by the ''usual'' click adjustments.

You see the virtual dot reflected on said mirror but - also see thru same to see target. Once reflection of red dot is adjusted to agree with gun's POA/POI requirements ..... you have it!!

Even ''cheapo'' red dots can be well useful ... it is a good habit to make dot sit central .... cos if some parallax errors then .. it'll still do pretty well. I favor quite long eye relief .... makes centering easier on cheapos. My old eyes now mean I have red dots on most all long guns ...... and even cheapo ones do better than me with irons!!

 

[CJ]

Ever since paintball, I've loved these things. My best way is to focus on the target with both eyes, bring the scope up and look through with your dominant eye, and the red dot will superimpose onto your target.

IMO, you get good eye relief with the 1x sight, quick target acquisition, and don't lose situation awareness by having to focus too tightly on a scope.

As for the moving around as you move your head...set the sight on a table and line up the dot with some target, look through and move your head around a little...the dot should stay on the target so that, wherever your head is, as long as you can see the dot, it's lined up with the target.

 

[TallPine]

With a scope, you want a consistent cheek weld to make sure there is either no parallax error (ie, it's centered) or it's as least consistent shot to shot.

That explains why I couldn't hit anything after I let a friend adjust the scope on my 22 rifle. I had to re-zero it for myself.

There is no "cheek-weld' on that rifle - because of the stock shape it is more like "chin-weld" with a scope. The stock is shaped for open sights.

 

[jamz]

THanks all, for the replies. It makes a lot more sense now. Can't wait to mount it on something!

-James

 

[ysr_racer]

I used to shoot a SA P-9 in 9x21 in IPSC matches with a dot.

The biggest advantage of a "red dot" is you can shoot with both eyes open. You look past the "scope" at the target and the dot is on it. It's much faster then iron sights.

 

[Jim K]

I am going to stick my neck out on parallax based on old memories and maybe someone will correct me if I am wrong.

Aside from sounding "neat" which is why the word is used in so many movies and sci-fi stories, it is real. It merely means that the appearance of two different points differs depending on the position of the viewer. This is easy. Pick a spot on the wall. Now put up the thumb of your right hand close to your eye and the thumb of your left hand farther away. With one eye closed, line the thumbs up with the spot on the wall.

Now, without moving your hands, move your head. Neither thumb is in line with the spot on the wall. That is parallax.

How does it occur in a scope sight? Here is where I have to go by memory, so bear with me and straighten me out where I goof.

A scope has an objective lens at the front. Light from an object (say a deer) enters that lens. The light is brought to a point (ever played with a "burning glass"?) then spreads out again but reversed. The deer's antlers are now at the bottom, and its left side is on the right. That image is "projected" on another lens, then a third lens or set of lenses magnifies and "erects" the image so it is right side up when you look in the scope.* If the crosshairs or dot is on the second lens, there will be no parallax. No matter how you move your head, the crosshairs or dot will always be fixed on the deer. But that is not feasible, since the lens would have to be movable and for mechanical and optical reasons that is not practical, though it has been done. (There are parallax free scopes though they are expensive.)

Normally, the crosshairs (or dot) will be somewhere in the scope where the image is "in the air", which means that they are not in the same optical plane as the picture you are looking at. And that difference is what causes parallax and results in the crosshairs seeming to move when your head moves.

*The same thing happens in the eye which does not have an erecting lens; the image on the retina is actually upside down. The brain reverses it or else we would see everything upside down, which would be a nuisance.

Jim

 

[Correia]

They are no gimmick. I've used iron sights for years, and I have a fraction of the amount of time on red dots in comparison, and I am much faster with a red dot. They dominate in competition for a reason. And you are seeing them in lots of pictures coming out of Iraq for the same reason. They are super fast and easy to use.

As for long distance shooting, I've used an Aimpoint and an EoTech out to 200 yards in a competition environment with no problems at all. I've shot them at ranges longer than that, but not extensively. If you can hit it with iron sights, you can hit it with a dot.