What Is Parallax?

[Sir Henry]

Yes I know what parallax is and can give you a textbook definition. But how much does it really affect accuracy? I have rimfire scopes preset at 60 yards and am wondering if my eye is offset slightly how much will I see off at 50 and 100 yards? How about a centerfire scope set for 150 yards. What if I’m shooting at 50 and 100 yards?

What does SF mean on a scope? Does it have anything to do with parallax?

[Cofisher]

Thanks for asking the question. I need to know more about this subject. I’m betting NCG has the definitive answer.

[GunnyGene]

SF means Side Focus. Basically it's the same as Adjustable Objective, and does the same thing. That is it allows you to adjust the scope to compensate for parallax at different distances. A SF scope will have 3 turrets, the one on the left is your parallax adjustment turret. Set it for the approx. range (or exact range if you know it) to your target. Magnification has an effect on parallax. Higher magnification will result in more of a parallax issue than lower magnification. More detail regarding setting order of power, focus, and parallax adjustment here:

https://www.leupold.com/riflescope-troubleshooting

[JEBar]

here is a link ====> https://www.youtube.com/watch?v=bEKt-bapfK4 to a short video that helped me understand what it is and how to fix it

[Sir Henry]

I think I understand the effect of parallax I want to know how much it really matters. If the scope is set for 60 yards and I’m shooting at 100 yards how far off the aim point will I shoot? Is it 3/8ths of an inch or three inches? Or even 8 inches?

On some scopes the eye box is so small it’s almost impossible to be that fat off center and not know it.

[GunnyGene]

I think I understand the effect of parallax I want to know how much it really matters. If the scope is set for 60 yards and I’m shooting at 100 yards how far off the aim point will I shoot? Is it 3/8ths of an inch or three inches? Or even 8 inches?

On some scopes the eye box is so small it’s almost impossible to be that fat off center and not know it.

Short answer is not much (assuming you have a fixed objective at 100yds, and don't crank in a lot of magnification). Just make sure you have a crisp reticle as noted in the link I posted. At 60 yds (or 140yds) the target will likely be slightly out of focus. Don't adjust your focus to bring the target into clearer focus. Keep your eye focused on the reticle. All parallax adjustment does is bring the target image into the same focal plane as the reticle, giving you crisp target and reticle images. I've never noticed any "floating" effect that video talked about.

Same as focusing on the front sight if you're using irons.

[Sir Henry]

I sure learned a lot today by doing a parallax check on some of my scopes. First of all I would like to say I checked at 75 yards and the distance was determined by this rangefinder.

FAB6C3EA-44B3-4A68-8BF2-D720507B3050.jpeg

I knew SF meant side focus (from reading) and have one.

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What confused me was I thought I had ordered the 4.5-14x50 SF 30mm. Now I remember they were out of stock and I ordered the 4.5-14x 50 1”. So when I received it without the third knob I thought it might mean something else. I think I’m getting senile.

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This is the scope that was on the CZ American I took to Texas and had problems. The picture below is where I experienced no movement for 75 yards. I’ve never had trouble with it befor but it seems it did not survive the 2,000+ mile trip.

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It took me about an hour to setup a stable platform and be able to sight out an open window. I was limited to open windows because I did not want to be aiming rifles in view of neighbors.

What really surprised me was the amount of parallax even between short differences. Easily two inches just between 60 and 75 yards. Aiming a rimfire scope with a fixed parallax of 60 yards would float the crosshairs a foot at 200 yards.

[JEBar]

I've never noticed any "floating" effect that video talked about.

I have noticed the crosshairs floating around but I've always assumed it was my natural wobble ..

[RanchRoper]

I thought parallax was something for constipation.

[Sir Henry]

I've never noticed any "floating" effect that video talked about.

I have noticed the crosshairs floating around but I've always assumed it was my natural wobble ..

I tend to make sure my eye is centered in the eye box and then check the crosshairs. What I’m learning is I need to be cross checking them and give the crosshairs priority in regards to no movement against the intended aim point.

Like I said earlier I could give you a textbook definition without understanding what it really meant. I was shocked at how much movement occurs between small differences from true parallax corrected distances.

[Sir Henry]

I thought parallax was something for constipation.

You might be onto something. I have been told I’m full of it.

[North Country Gal]

Gene, parallax matters IF you need the absolute best the rifle can deliver in terms of accuracy. For instance, if you are hunting small varmints at various distances, parallax error can absolutely cause a miss. On the other hand, for big game hunting with a kill zone that is much larger, parallax error is usually not a factor and no need to add an AO or SF to the scope. In fact, having an AO or SF can introduce enough error to miss if you inadvertently have it set at a setting that is way off for the distance you are shooting. Most big game hunters prefer to keep it simple and leave the AO or SF to their varmint or target scopes.

It is important to note that parallax is going to be more of an issue when you are shooting closer than the the factory focus setting for the scope, compared to shooting at a greater distance than the factory setting. For instance, with a scope that is factory focused at 150 yards as most big game scopes are, parallax is going to be fairly minimal at twice that distance or even more. On the other hand, with the same scope set at 150 yards, there will be considerable parallax error up close at 50 yards and even more at 25 yards. This is because parallax becomes more serious at closer distances.

A great example of this is in air gun shooting where shots are usually 50 yards or less. Seems counter intuitive, but parallax at a measly 10 yards distance is huge even with a rimfire scope that is set to be parallax free at 50 yards. Parallax is such an important issue at these typical short air gun distances that you cannot compete in air gun target competition without a scope with an AO or SF. Your rimfire scope on an airgun will work fine for shots past 30 yards or so, but it will have too much parallax to allow you to shoot your best at closer distances and, keep in mind, that a lot of air gun competition is at 10 meters.

In fact, when I use red dots on air guns at 10 meters, I have parallax error. Marketing with red dots that proclaim the red dots are parallax free at all distances is, uh, I'll be nice and say a white lie. Red dots are almost universally set to be parallax free at 50 yards, but up close at 10 meters, every red dot I've tried has parallax and some models have a lot of parallax, way, way too much when shooting for score at 10 meters.

In air rifle Field Target competition where shots range out to just under 50 yards or so, competitors actually use their SF or AO as rangefinders by focusing until the scope is at its sharpest and there is no movement of the reticle, then checking the distance markings on the SF or AO, since range finders are not allowed in competition.

Each and every one of my airguns with a scope have an AO. All my rimfires with scopes also have an AO, because I'm typically sooting for the smallest possible group size on one inch dot targets and one day I may be shooting up close at 20 yards and 100 yards the next. Granted, I'm something of an accuracy fanatic, but I know from experience that parallax is an issue for my shooting. In fact, with my air gun and rimfire shooting, I always check for parallax. It's easy to check and when you make a habit of it, you'll be surprised just how much that reticle can move at times.

Lastly the yard/meter marking on an AO or SF are simply more of a suggestion than anything truly precise. You really have to focus the scope with the AO at a known, measured distance until parallax disappears and then mark the distance yourself on the AO if you want to eliminate any chance of parallax error.

[Sir Henry]

Thanks Joanie, it really explains why my scoped CZ scout which I wanted for strictly 25 yards was all over the place. I thought it was the rifle and now think it was the close distance.

I was able to find a spot outdoors where I could aim at 25, 45 and 64 yards with the scout. Lots of movement at 25, a fair amount at 45 and very little at 64.

I was wondering if what I perceived at 64 was less movement or if it appeared less because of the greater distance. Kind of like one inch at 25 is the same as two inches at 50.

[North Country Gal]

Try higher magnification if the scope has it. That will make crosshair movement more obvious. Remember, it's movement of the reticle relative to a fixed point or target of constant size you want to check. For instance, if I use a one inch orange dot, I can estimate how much parallax there is by how much movement of the crosshair I get relative to that size of dot at varying distances. Does the crosshair stay centered in the dot, move to the edge of the dot, move outside the dot and so on as I move my eye side to side, up and down. If that reticle does not stay perfectly centered in that one inch dot at 50 yards, then, I know it's going to be tough to shoot the smallest possible group. I use one inch orange dots as my standard target when shooting for group size with a scope because I can better see the crosshair against orange than against a black dot.

Or if you have a larger bull with scoring rings, the scoring rings make a good way to measure, assuming you have a scope with good optics and enough magnification. Again, just use the same target at the varying distances.

One more. In theory, if you can place your eye in EXACTLY the same point behind the scope for every shot, shot after shot, you can eliminate the parallax problem. Having a stock with a target comb that allows you to place your face on the stock, comfortably, is a plus, but even so, we humans are not robots. Shooting technique is already complex enough for most of us, so we don't need to add another thing to it.

[Sir Henry]

Where I can aim a rifle outside and not be seen limits where I can aim. Unfortunately that takes me to the neighbors shed where I can’t place a bullseye.

The ability to absolutely center your eye is what makes me a three hit wonder. The amount of concentration it takes is fatiguing.

I just checked online and my Leupold scopes are 60 and 150 yards for rim and center fire respectively. I knew that in general but confirmed for my particular scopes.

The Nikon scopes are 50 and 100 yards and I did not know that. I shoot at those distances the most. There is no hash marks on our range for 60 yards although there is for 150.

It is amazing how little I knew about parallax. Now I’m wondering about my two degree scope cant. I think I need to level them more precisely.

[Sir Henry]

Another question: is there any parallax on a one power scope? I understand it might not be perceived but am wondering if it’s still there.

[North Country Gal]

All optical systems have parallax. Yes, there is parallax in a 1x scope. Note what I said about red dots, which are 1x. Even with their simple optical systems, they have parallax. A few years back, I was on the prowl for a scope that would not have parallax so I could shoot it at 10 meters for my airgun shooting. I tried some 1x muzzleloading scopes. No go. At 10 meters I could still get the crosshairs to move out of the 9 and 10 ring.

Hey, don't lose any sleep over parallax. Just get the scope or optics that best suits your shooting needs and for most folks that's still a scope without an AO or SF. If I was still small game hunting with a 22, I'd go right back to my favorite rimfire scopes that had no AO or SF. If I was still deer hunting and using a scope, I wouldn't loose any sleep over parallax. For plinking, shooting steel, recreational shooting, and so on, you don't need an AO or SF scope. In all these types of shooting and more, just get a scope that is factory set to be parallax free in the neighborhood of your expected shooting distance.

It's when you start sweating over shaving another tenth of an inch off of group size or where that tenth of an inch or even less can cost you a match or a miss on a tiny target out at 200 yards, that you should start thinking about an AO or SF scope. Since all air gunning is done in that parallax critical close up zone and no one actually makes scopes set to be parallax free at 20 or 25 yards or 10 yards (outside of a few specialty air gun scopes), AOs or SFs are standard equipment. Even so, a lot of air gunners still use red dots and rimfire scopes with no AO for plinking and shooting steel.

[GunnyGene]

Adjustable parallax capability is a fairly new invention. Carlos Hathcock used a 8x Unertl scope in VN, which didn't even have a mil-dot reticle, let alone any way to adjust for parallax.

[Sir Henry]

Adjustable parallax capability is a fairly new invention. Carlos Hathcock used a 8x Unertl scope in VN, which didn't even have a mil-dot reticle, let alone any way to adjust for parallax.

He had the record for distance for several decades. It’s amazing he could get a kill at a mile with an 8x.

[GunnyGene]

Adjustable parallax capability is a fairly new invention. Carlos Hathcock used a 8x Unertl scope in VN, which didn't even have a mil-dot reticle, let alone any way to adjust for parallax.

He had the record for distance for several decades. It’s amazing he could get a kill at a mile with an 8x.

Here's a little more on that Unertl and rifle.

https://sofrep.com/gear/the-carlos-hath ... per-rifle/