focus parallax

[kkayser]

On the Nikon Monarch and the Sightron SIII scopes, parallax and focus are the same knob. What happens if best focus and zero parallax are not at the same position of the one knob? Do you get to choose one or the other?

[Rover]

You might try playing with this:

http://www.rimfirecentral.com/forums/sh ... adjustment

[Isabel1130]

On the Nikon Monarch and the Sightron SIII scopes, parallax and focus are the same knob. What happens if best focus and zero parallax are not at the same position of the one knob? Do you get to choose one or the other?

Neither of these issues are of critical importance when shooting pistol. The furthest distance is 50 yards, and there is no "focus" required in a red dot scope. You might encounter a little parallax error if you don't keep the dot centered in the tube, but it should not be significant enough to cost you any points.

[kkayser]

You might try playing with this:

http://www.rimfirecentral.com/forums/sh ... adjustment

That's very helpful for those who own a "non-parallax adjustable" scope. I am buying a new scope and want to use it at different ranges and on different rifles. I do not want to disassemble it. I would like 3 knobs: reticle focus, target focus, parallax adjustment. Does anyone know if such a scope exists?

[Isabel1130]

You might try playing with this:

http://www.rimfirecentral.com/forums/sh ... adjustment

That's very helpful for those who own a "non-parallax adjustable" scope. I am buying a new scope and want to use it at different ranges and on different rifles. I do not want to disassemble it. I would like 3 knobs: reticle focus, target focus, parallax adjustment. Does anyone know if such a scope exists?

No, but if you posted in a high power rifle forum, you might have better luck finding a good technical answer.

[kkayser]

I do intend to use the scope on a .22 rifle. Even inexpensive ones like the Czeck (about $400 and change) will hold 1" groups at 100yds. So, 1/2 MOA of parallax error is very significant.

I'll try an HP rifle forum, but I think I have a pretty good idea of the problem.

I think that makers build scopes so that zero parallax and target sharpest focus are the same for 20/20 vision. Of the two, parallax would seem to be more important. If the bull is a little blurred, one can still center the cross hairs, and the hit point and aim point will be the same. However, if there is parallax error, the hit point and aim point will be different.

Ideally, there should be three knobs: reticle focus, target focus, and parallax adjustment. Does anyone know if such a scope exists?

Lacking 3 knobs, it would seem that one would have to try different scopes to see which is best for your aiming eye.

[Justin Credible]

You might try playing with this:

http://www.rimfirecentral.com/forums/sh ... adjustment

That's very helpful for those who own a "non-parallax adjustable" scope. I am buying a new scope and want to use it at different ranges and on different rifles. I do not want to disassemble it. I would like 3 knobs: reticle focus, target focus, parallax adjustment. Does anyone know if such a scope exists?

Assuming the reticle is focused properly, target focus and parallax adjustment are the same thing. Parallax is eliminated when the image of the target is focused on the reticle, so focusing the target eliminates parallax.

I think people run into issues with this by not having the reticle focused properly using the eye piece. Then when you try to focus the target with the AO/parallax knob your eyes do some accommodation and the reticle is out of focus but you don't realize it as the brain is merging the focused reticle and the focused target into one image as your eye goes back and forth between focusing on the two. Getting a good reticle focus with the eyepiece, best done by using a background you can't focus on such as the blue sky or white cloth over the objective, is the key.

When I adjust my objective on an AO scope I just get the target focused, knowing my eyepiece is focused, and then I know I'm parallax free without trying to move my head around and whatnot. I have heard people say that their parallax adjustment can change for a given distance over time. The real problem is that their eye changes and that they need to adjust the eyepiece to proper reticle focus.

Justin Tracy

[kkayser]

Justin Tracy[/quote]

Assuming the reticle is focused properly, target focus and parallax adjustment are the same thing. Parallax is eliminated when the image of the target is focused on the reticle, so focusing the target eliminates parallax.

I think people run into issues with this by not having the reticle focused properly using the eye piece. Then when you try to focus the target with the AO/parallax knob your eyes do some accommodation and the reticle is out of focus but you don't realize it as the brain is merging the focused reticle and the focused target into one image as your eye goes back and forth between focusing on the two. Getting a good reticle focus with the eyepiece, best done by using a background you can't focus on such as the blue sky or white cloth over the objective, is the key.

When I adjust my objective on an AO scope I just get the target focused, knowing my eyepiece is focused, and then I know I'm parallax free without trying to move my head around and whatnot. I have heard people say that their parallax adjustment can change for a given distance over time. The real problem is that their eye changes and that they need to adjust the eyepiece to proper reticle focus.

Justin Tracy[/quote]

I called Sightron and was told that target focus and parallax are not necessarily the same, but that the difference is insignificant. You seem to be telling us that reticle focus affects parallax. I never heard that before, but we'll see next spring. Right now it is about 10 deg and snowing. I'm a fair weather shooter. Until it gets above 50 deg, I will be shooting my air pistol in the basement.

[Justin Credible]

I called Sightron and was told that target focus and parallax are not necessarily the same, but that the difference is insignificant. You seem to be telling us that reticle focus affects parallax. I never heard that before, but we'll see next spring. Right now it is about 10 deg and snowing. I'm a fair weather shooter. Until it gets above 50 deg, I will be shooting my air pistol in the basement.

I think it's more correct to say that poor reticle focus prevents one from properly adjusting the objective focus to remove parallax. A scope needs to be adjusted so that the focal plane of the objective is on the reticle and the eyepiece is focused on the reticle. When they all line-up there is no paralax. If the reticle is not focused FIRST, then adjusting the objective properly goes out the window. Adjusting the reticle focus is not how you fix parallax, but it must first be correct to fix parallax.

I can't aregue with shooting air when it's that cold!

Justin Tracy

[DLS]

I called Sightron and was told that target focus and parallax are not necessarily the same

Whomever you talked with at Sightron didn't do you any favors with the explanation given. They are not correct in what they say, and they should have better described why. Eliminate the word 'necessarily' and they would have been correct, because these two items are NOT the same.

Parallax is a CONDITION caused by improper focus. It is cured by proper focus. That is why you don't see scopes with the third adjustment knob that you seek, because it's not necessary, or even possible. You can't create an adjustment knob for a "condition", only for what causes the condition.

Clear as mud?

Definitions of parallax that apply to a scope used on arms:

1. The apparent displacement of an observed object due to a change in the position of the observer.

2. An apparent change in the position of cross hairs as viewed through a telescope, when the focusing is imperfect.

So, if your target focus is precise you eliminate all parallax at that particular range. You will have parallax at any other range. This is why target scopes allow for an adjustment as target shooters shoot at different ranges (I know you know this, just wanting to be complete in my post).

Additionally, the advice about reticle focus is very sound. It's virtually impossible to perfectly focus on the target when the reticle is out of focus. You may be able to get close, but there will always be some amount of error. So the very first scope adjustment should be to focus the reticle to your eye. This focus should be tested from time to time, as our vision changes with time, sometimes even enough over a multi-day shoot to warrant refocusing.

I hope this helps.

Lee

[DLS]

I should also add that none of this may really matter in the end.

Over the ranges that pistol is usually fired the amount of apparent reticle displacement will not move you out of a scoring ring assuming that the target focus is remotely close to the range you are shooting.

If you are using a fixed objective rifle scope on a center-fire pistol (say a metallic silhouette rig) and are shooting close in it may make enough difference to care, but would anyone do this in a competitive setting?

Most non-adjustable rimfire and pistol scopes are set to be parallax free at 75 feet, which means anything from 10m to 50m will not be a problem.

Even if you are shooting rimfire out to 100 yards, the apparent movement of the reticle on a fixed adjustment scope would not move you out of any scoring ring on any of the NRA type targets.

Again, this really is a moot point anyway. You say you want to shoot 100 yards with your rimfire. Well in prone your stock/cheek weld holds your eye in the same position in relation to the eyepiece, and the position is so stable that you should not see any apparent movement, even if there is a large amount of parallax.

Snipers have used fixed objective scopes for years (beyond Viet Nam). Most of these scopes were manufactured to be parallax free at ranges from 150 to 300 yards (since most were adaptations of sporting scopes), yet snipers routinely take and make shots at 700 + yards. Parallax is not an issues even here, if the position is stable.

Of course you would like to remove all impediments to success, so sniper scopes now incorporate adjustable objectives, but most guys in the field set them once (to say 500 - 700 yards in open terrain maybe a tad more) and then forget about it, relying on there position to take care of the rest.

Okay ... sorry ... long winded ... I apologize!

[Chris__Colorado]

Parallax induced error is negligible if you can consistently put your eye in the same place when you shoot.
Based upon some equations, here's some quantitative analysis
http://www.network54.com/Forum/79537/th ... objectives
Bottom Line, if you are shooting between 10m and 100m and you set your AO to 55m (midpoint), worst case (maximum) parallax error is .81 inches for a target at 100m. This worst case error will NEVER happen for two reasons:
1. Your eye is so non-centered in the scope that only a single ray of light makes it through and you would not be able to see the target. I hope that you won't pull the trigger in that state.
2. Your target will be out of focus and you will adjust your AO to bring it into focus for precision shooting, which will reduce the "maximum" parallax error to near zero (eye way off center), and virtually zero if you center your eye in the scope.
If you consistently center your eye in the scope, there are other sources of error that are more significant than parallax error (reading the wind, knowing target distance for adjusting drop, velocity variation, trigger pull, sight picture, sight alignment, etc).
Hope this helps.
Chris
PS I learned that parallax error is independent of magnification, and only dependent on Object Lens size and the difference between the AO setting distance (what it's focused on) and the target distance.
PPS This assumes the equation that I modeled years ago was correct.
Take away: Parallax error is not something I am concerned about as other factors are way more significant.

[DLS]

Parallax induced error is negligible if you can consistently put your eye in the same place when you shoot.
Based upon some equations, here's some quantitative ...

This is exactly what I was trying to detail when shooting prone. Your stock weld is very easy to replicate ensuring your eye is in the same place each shot. So even at ranges of over a thousand yards, you don't need to worry about it.

You just said is better!


Great post Chris__Colorado.

[Chris__Colorado]

So even at ranges of over a thousand yards, you don't need to worry about it.

I've seen this discussed many times over the years, so I finally broke down and basically modeled it to determine the effect of parallax errors.

If you have your shooting fundamentals down,

you don't need to worry about it.

perfectly sums up the net effect of parallax error given all the other variables influencing accuracy and precision.

Here is the link to the file (AO_Calc_Table_....xls) in case anyone wants to play with determining the maximum possible errors.

http://sdrv.ms/1kWebxD
https://skydrive.live.com/redir?resid=B ... 6281%21120

[DLS]

This is getting far afield from Olympic style shooting, but since we have already started on the path ... <grin>

AO scopes are really not all that valuable for sporting purposes (in my opinion) with a few exceptions.

Silhouette shooting uses inherently unstable positions (i.e. standing with the rifle and the"taco hold" with a pistol) and high magnification scopes, sometimes up to 36x! Even a "good holder" is going to have a lot of visible movement in their sight picture. So anything to minimize the visible movement is a benefit, especially considering how small the target is (in terms of MOA).

I can see an argument for benchrest as well. Even though stock weld can be replicate quite nicely on a benched gun, we are talking thousands of an inch differences between winning and ho hum results. Even here though, if the shooter is paying close attention it really doesn't matter.

I was a Marine from 77-83, and our sniper rifles (M40A1's) mounted what was pretty much a stock 3-9x Redfield scope (upgraded reticle by Premier) that was manufactured parallax free at 150 yards (if memory serves). There were some fixed power Unertl's floating around too, but I never played with them. I think the were 10x and they too were manufactured with a 150 yard setting.

We routinely engaged targets to 1200 meters. I cannot remember parallax ever being an issue when we missed. There were plenty of other issues far more "impactful" in where the shot ended up!

Lee

[Chris__Colorado]

To help get us back on target, I've calculated the maximum possible parallax error for the various scope objective lens sizes, at the distances for Bullseye, at various AO settings (and mismatches).

The results are in the attached PDF file.

Enjoy!
Chris

[FredB]

It's been interesting reading these posts from 2 people who seem to know what they are talking about. So - and this brings the topic back to bullseye shooting - what about parallax in red dot sights? I have several red dot sights, and some of them show what I've always interpreted as significant parallax.

Suppose I immobilize the sight (usually mounted on a gun which is immobilized) and center the red dot on a distant target while keeping the red dot centered in the sight's lens. With several of my sights, if I then move my head so that the dot appears to move from side to side or up and down, the dot also appears to move a pretty good distance off target center.

In bullseye there's no cheek weld to help keep the dot centered, and it can move around quite a bit. Since the bullet is supposed to hit where the red dot is at the moment of firing, doesn't this mean there can be significant parallax error? Of course there can be many other errors in bullseye, and of course I could be misunderstanding how to evaluate parallax in a red dot sight, but it seems to me that parallax error could be non-trivial with some red dot sights.

FredB

[DLS]

Like a traditional telescope, Red Dots are only parallax free at one range. In the end, just like a telescope it really doesn't matter for several reasons.

One is that the effect is minimized because reflex sights don't have magnification. In a magnified scope the apparent movement is increased by a factor of the scopes magnification.

Another reason is that the maximum displacement is limited to half the objective diameter in the worst case scenario and just like the telescope, you have to displace your eye to the far edge of the field of view to get to this worst case scenario. I know it seems there is a lot of movement, but give this a try.

Clamp the gun with the sight on the bull at the proper range. Watch someone move their head from side to side as they try an move the dot from one edge of the bull to another. It will amaze you how much the head is actually moving, far more that would ever happen when shooting.

Then do the exercise yourself. It will feel like you are hardly moving your head, but in actuality you are moving your head as much as the other guy.

So in the end, in normal shooing posture you will never have enough dot movement to pull you out of a scoring ring, you won't even come close!

That's why manufactures call reflex sights "parallax free" because in essence they are in any normal sense of how they would be used.

A good link for this topic is:

http://www.bullseyepistol.com/dotsight.htm

Note that the example of the poorer performing scope is worst case, requiring you to have your eye all the way out of position. In normal shooting situations you would never leave the X-ring.

I hope this helps.

[kkayser]

The reticle is "in focus" when the image of the reticle on the retina is sharp. But, the lens in the eye is flexible and changes from thick to thin to be able to focus on objects near to far. So, where should the focus of the lens of the eye be when the ocular is adjusted? Infinity? If so, might this work? First focus the eye on a distant object, then look in the ocular, if the reticle looks sharp, ok. If the reticle looks unsharp at first, then sharpens, the ocular needs adjusting.

I have decided what I am going to do. I will buy a scope from someone (probably Amazon) who will give me a 30 day trial. At the range, I will see if I can adjust the ocular and the side focus/parallax to give sharp images of the reticle and target, and zero parallax. If so, I will keep the scope, if not, I will try another scope.

[DLS]

The reticle is "in focus" when the image of the reticle on the retina is sharp.

Yes exactly

This is done while NOT focusing on anything. The best way to do this is to look into a cloudless sky. Quickly glance at the reticle and note its sharpness. If not sharp make an adjustment (on the ocular or eyepiece end of the scope). Look away for a few moments, then glance at the reticle again. Keep doing this until you can't get the reticle any sharper.

The reason you glance is that your eye will try and accommodate an unfocused object by changing its own focus. It you look at the reticle for more than a moment, this will happen (it's hard wired into our vision system, you can't override this with conscious effort). So only take quick glances and note the sharpness of the reticle. Make sure you look away for a few seconds before you glance again, this allows your eye's accommodation to return to a relaxed state.

If you can't access the sky, a large blank neutral colored wall will do, make sure you have even light falling on the wall so there are no shadows or contrasts.

Once you have a fully sharp reticle, this part of the scopes focus procedure is done. By the way, do this wearing whatever lenses you will use when shooting, whether they be prescription or just safety lenses, as any lens (even one without corrections) imparts some affect on the vision.

This focus should be checked from time to time, as you eyes acuity changes a tiny bit day by day, even hour by hour. So this focus will need to be reset occasionally. Do this any time you change prescription lenses etc.

I have vision problems, have had retinal surgeries and have an artificial lens in one eye. I have two prone rifles, one I use inside gallery shooting, the other outside. Once scope's reticule is focused when I wear my prescription lenses the other without, because the range I'm shooting at determines if I need my glasses or not. Does this make sense?

But, the lens in the eye is flexible and changes from thick to thin to be able to focus on objects near to far.

Which is why we only glance at the reticle while focusing, to avoid this from impacting the focus setting and having the result of a "nearly" focused reticle that appears totally focused because of our eyes unconscious accommodation.

So, where should the focus of the lens of the eye be when the ocular is adjusted?

Underline and bold font added by me in the quote above.

The eye should focus on the reticle at all times, when focusing the scope's reticle, when focusing the target, and when shooting.

Infinity? If so, might this work? First focus the eye on a distant object, then look in the ocular, if the reticle looks sharp, ok. If the reticle looks unsharp at first, then sharpens, the ocular needs adjusting.

No, use the procedure listed earlier. Trying to focus the reticule as you just suggested will make it very difficult to end up with a properly focused reticle.

... I will buy a scope from someone (probably Amazon) who will give me a 30 day trial.

Most scopes are not returnable once they have been mounted in rings, unless they are defective. It's highly unlikely any modern scope will not be able to achieve reticle focus, but it could happen. I've never seen it personally.

At the range, I will see if I can adjust the ocular and the side focus/parallax to give sharp images of the reticle and target, and zero parallax.

Once the reticle is focused, you can now focus the target by using the objective end adjustment, or if available a side mounted knob. Remember,

Once the target is in focus there is ZERO parallax at that particular range.

All scopes will only be parallax free at ONE range only, even the adjustable ones.

By the way, you don't need to go to the range to do this, you don't even need to mount the scope. You can do it hand holding the scope in your backyard. All you need is a clear sky for reticle focus, and something at a distance that approximates your shooting distance to then look at to set the objective adjustment.

I do this in the store when I'm looking to by a scope directly from a vendor. If I mail order, it's the first thing I do once the scope comes out of the box.

If so, I will keep the scope, if not, I will try another scope.

If you can't set up the scope it will most likely be what you are doing, and not the scopes fault, but again, there are rare cases where the focus elements of a scope get past quality control.

Long-winded again, sorry! I hope this helps.

I might add one thing to all of this ... why pay the additional cost of an adjustable objective scope? They are more complex, weigh more, cost more, add additional failure points to the system and for all intents and purposes will not give you ANY benefit at all. It's much more about marketing than precision shooting.

At the clubs where I shoot, I still see about 1/3 of the benchresters using older non-adjustable scopes. They usually win, and they are not afraid to drop big money on equipment if it will shrink their groups, so it's not because they are broke or cheap. We have already discussed how long-range shooting really does not need this adjustment either.

So I'm curious as to why you are so worried about it? By the way, there is nothing wrong in your considering all of this so please don't take it that way!

Just food for thought.