How do you dial out parallax?
- Thread starter mao0720
- Start date
Same above process and fine tuning moving my head until a fully firm crosshair
I think many shooters confuse or assume the parallax knob or side focus knob as we often refer to it as jus that, a focus knob. Parallax is the apparent movement of the crosshairs in the sight picture in relation to the target. In other words, having your rifle set steady and aimed at a target, if your parallax is not set the crosshairs will appear to move across the target in the opposite direction you move your head as you look through your scope. Move your head left and the crosshairs appear to move across the target to the right. This is the movement you are trying to reduce. Continuing to look through your scope, slowly adjust your parallax knob while slightly moving your head left and right. As you adjust you will notice the movement of the crosshair will become less and less until there is no longer any movement and the crosshairs are staying exactly on the aiming point. Your parallax is set.
Yes, the target does become more focused as you are doing this process, but what you perceive as focused (we all have different vision circumstances, good or bad) may not yet be your optimal parallax setting. Do not rely on the yardage markings on your scope knob. I have a few scopes, good decent scopes (sightron SIIIs), that do not match up the yardage marking with the correct parallax setting.
Hope this helps
Yes, the target does become more focused as you are doing this process, but what you perceive as focused (we all have different vision circumstances, good or bad) may not yet be your optimal parallax setting. Do not rely on the yardage markings on your scope knob. I have a few scopes, good decent scopes (sightron SIIIs), that do not match up the yardage marking with the correct parallax setting.
Hope this helps
^ +1
My scope, when parallax is properly adjusted, is NOT at best "focus". The fastest way for me to do it is to "focus" the scope for clarity at the distance we are shooting, then fine tune it using the head movement method described above.
My scope, when parallax is properly adjusted, is NOT at best "focus". The fastest way for me to do it is to "focus" the scope for clarity at the distance we are shooting, then fine tune it using the head movement method described above.
Turbulent Turtle
F-TR competitor
It might be good to understand what parallax is so as to be able to deal with it.
The concept of a riflescope is to present to the shooter's eye the reticle (aiming point) superimposed on the picture of the objective on the same focal plane.
The reticle is at a fixed distance in the riflescope and the first thing to do when you first use the riflescope is to focus the eyepiece so that the reticle is nice and crisp. You do this by aiming at a blank wall or the sky, something that you don't focus on, your eye is on the reticle only. Parallax is when the objective lens puts the target in a focal plane that does not coincide with the reticle; it is either in front of or behind the reticle and when your head moves, you can see that the two are not lined up solidly. The goal here is to have a crisp reticle superimposed on a crisp picture of the target and at that point, the parallax is gone.
How do we do this?
When you look through a scope you aim it at your objective and that's where you encounter the first property of a riflescope, focus. Every scope, camera lens, binocular, monocular, etc., needs to be focused so as to present a crisp image of the objective to the sensor, be it your eye, film, photocell, etc. The focus is predicated on the distance to the objective, but there are many factors that influence the picture that is detected behind the scope.
There is something called depth of field that come into play right off the bat. Think of this as the area in front of and behind the objective that still appears to be in focus. When your objective is close, the depth of field is actually pretty narrow; the closer the objective, the narrower the depth of field. You can verify this by simply holding a finger up to your eye and focusing on it. Whatever is behind goes immediately out of focus. As you extend your arm and still focusing on your finger you notice the background rapidly comes into focus.
So the further away your objective is, the wider the depth of field. Another factor that influences depth of field is magnification. A 3X scope has a much wider depth of field when focused at 100 yards than say a 40X scope does.
Another factor that affects depth of field is aperture size; the wider the aperture the narrower the depth of field. However since there are no aperture controls on a rifle scope or other similar objects, except for camera lenses, this is not something that we can do anything about. I'm just mentioning it here for completeness.
Having a wide depth of field, does not eliminate parallax, it actually makes it a little more difficult to dial out. I'll explain in a minute and give you a hint to help deal with it.
As I said at the beginning, you need to start with the reticle in perfect focus for your eye. The reticle does not move, that's your baseline. Now that you have the best picture of the objective, you want to adjust the image of the target to be at its crispest, which will also be on the focal plane of the reticle. This will give you a parallax-free picture of the reticle on the target.
There are two ways to adjust the focus in a rifle scope to get the crispest picture of the target; an adjustable objective or a side focus mechanism. The adjustable objective is exactly that, you crank the objective lens, that big one at the front of the scope, to get the crispest image of your objective you can get. This is the easiest and also the most accurate method of adjusting for the parallax. Once the reticle is crisp and the target is crisp, you have a parallax-free image; put the reticle where you want on the target and pull the trigger.
The other method is the side focus. I'll be the first to admit I'm not completely clear on exactly how it does it, but I understand there is an extra lens in the mechanism and I suspect that instead of adjusting the objective lens to focus, this mechanism alters the focus plane of the objective with that extra lens. At any rate, it does the job at the price of another lens, heavier mechanism and extra complexity and cost. I have some scopes that have adjustable objectives and others that have side focus. The former are easier to focus, but the latter are easier to use from position. For competitions like F-Class, an adjustable objective is probably better than a side focus, but alas, most high end scopes use the side focus.
A side focus should not be adjusted from one distance to another, unlike an adjustable objective. Instead, it should be adjusted starting from infinity down to the target, for best results. I know most people just go from one to the other and I have done that, but it is better to go back to infinity and dial in.
Now, you are probably wondering what all that discussion about depth of field was about. And where is this hint I mentioned, you may ask.
Scopes that do not have any way of adjusting the objective rely on depth of field. The scope is focused for a set distance and is low enough in power as to have the image pretty much in focus to handle all distances, but the focus is set at a specific distance and at that distance, the image is parallax-free. Usually that is 100-150 yards depending on the manufacturer.
When you have an adjustable objective, the trick is making sure you have the scope focused at the proper distance and a large depth of field makes that difficult to ascertain, because the target is in focus early on and stays in focus for a long way. It's like going to the optometrist and flipping through lenses being asked if this one is better or that one.
Remember when I said that depth of field shrinks as magnification increases? Make sure you set the objective or side focus at the maximum magnification of your scope. I know a lot of people dial back from maximum during the summer, but you should always use maximum mag to set the focus.
The concept of a riflescope is to present to the shooter's eye the reticle (aiming point) superimposed on the picture of the objective on the same focal plane.
The reticle is at a fixed distance in the riflescope and the first thing to do when you first use the riflescope is to focus the eyepiece so that the reticle is nice and crisp. You do this by aiming at a blank wall or the sky, something that you don't focus on, your eye is on the reticle only. Parallax is when the objective lens puts the target in a focal plane that does not coincide with the reticle; it is either in front of or behind the reticle and when your head moves, you can see that the two are not lined up solidly. The goal here is to have a crisp reticle superimposed on a crisp picture of the target and at that point, the parallax is gone.
How do we do this?
When you look through a scope you aim it at your objective and that's where you encounter the first property of a riflescope, focus. Every scope, camera lens, binocular, monocular, etc., needs to be focused so as to present a crisp image of the objective to the sensor, be it your eye, film, photocell, etc. The focus is predicated on the distance to the objective, but there are many factors that influence the picture that is detected behind the scope.
There is something called depth of field that come into play right off the bat. Think of this as the area in front of and behind the objective that still appears to be in focus. When your objective is close, the depth of field is actually pretty narrow; the closer the objective, the narrower the depth of field. You can verify this by simply holding a finger up to your eye and focusing on it. Whatever is behind goes immediately out of focus. As you extend your arm and still focusing on your finger you notice the background rapidly comes into focus.
So the further away your objective is, the wider the depth of field. Another factor that influences depth of field is magnification. A 3X scope has a much wider depth of field when focused at 100 yards than say a 40X scope does.
Another factor that affects depth of field is aperture size; the wider the aperture the narrower the depth of field. However since there are no aperture controls on a rifle scope or other similar objects, except for camera lenses, this is not something that we can do anything about. I'm just mentioning it here for completeness.
Having a wide depth of field, does not eliminate parallax, it actually makes it a little more difficult to dial out. I'll explain in a minute and give you a hint to help deal with it.
As I said at the beginning, you need to start with the reticle in perfect focus for your eye. The reticle does not move, that's your baseline. Now that you have the best picture of the objective, you want to adjust the image of the target to be at its crispest, which will also be on the focal plane of the reticle. This will give you a parallax-free picture of the reticle on the target.
There are two ways to adjust the focus in a rifle scope to get the crispest picture of the target; an adjustable objective or a side focus mechanism. The adjustable objective is exactly that, you crank the objective lens, that big one at the front of the scope, to get the crispest image of your objective you can get. This is the easiest and also the most accurate method of adjusting for the parallax. Once the reticle is crisp and the target is crisp, you have a parallax-free image; put the reticle where you want on the target and pull the trigger.
The other method is the side focus. I'll be the first to admit I'm not completely clear on exactly how it does it, but I understand there is an extra lens in the mechanism and I suspect that instead of adjusting the objective lens to focus, this mechanism alters the focus plane of the objective with that extra lens. At any rate, it does the job at the price of another lens, heavier mechanism and extra complexity and cost. I have some scopes that have adjustable objectives and others that have side focus. The former are easier to focus, but the latter are easier to use from position. For competitions like F-Class, an adjustable objective is probably better than a side focus, but alas, most high end scopes use the side focus.
A side focus should not be adjusted from one distance to another, unlike an adjustable objective. Instead, it should be adjusted starting from infinity down to the target, for best results. I know most people just go from one to the other and I have done that, but it is better to go back to infinity and dial in.
Now, you are probably wondering what all that discussion about depth of field was about. And where is this hint I mentioned, you may ask.
Scopes that do not have any way of adjusting the objective rely on depth of field. The scope is focused for a set distance and is low enough in power as to have the image pretty much in focus to handle all distances, but the focus is set at a specific distance and at that distance, the image is parallax-free. Usually that is 100-150 yards depending on the manufacturer.
When you have an adjustable objective, the trick is making sure you have the scope focused at the proper distance and a large depth of field makes that difficult to ascertain, because the target is in focus early on and stays in focus for a long way. It's like going to the optometrist and flipping through lenses being asked if this one is better or that one.
Remember when I said that depth of field shrinks as magnification increases? Make sure you set the objective or side focus at the maximum magnification of your scope. I know a lot of people dial back from maximum during the summer, but you should always use maximum mag to set the focus.
Many assume that the markings on the parallax knob are correct. Sometimes they are and sometimes not. What has helped me most is to set your diopter by setting your zoom to highest power, sight on a light background like blue sky, then adjust the diopter all the way both ways so you can see the contrast. Then set it to the point that the stadia are the darkest. I've got mine marked because it's easy to turn it slightly and none of my scopes have a locking diopter ring. Then I check my markings on my parallax knob to see how close they are by ranging targets and adjusting all the parallax out and checking where the setting is. The scope I use most the markings for focus are way off (Vortex Razor Gen II) The nice thing is after 200 yards I can just adjust it to infinity and that gets rid of the parallax and keeps the focus adjusted well.
Keep in mind, what you perceive to be the "crispest" target picture does not necessarily mean you are free of parallax. The only way to ensure is to use the head movement method described above until all movement of the reticle on target is gone.
I never use the markings on the parallax knob to set my focus or parallax, but admittedly I do usually just dial in to the clearest focus and start shooting. Im really going to have to start using the head movement technique to make sure Im getting parallax out before I start a string of fire. Im curious to see if it will make a significant difference in my scores.
Mason O said:
+1!
Bruce
Turbulent Turtle
F-TR competitor
simplerider said:
Let me put it this way. If you still have parallax issues after you have focused your scope to have what you consider the "crispest", sharpest, most in focus picture of the target possible, you didn't focus well enough.
It can be difficult, especially at lower magnification and longer distances, which is why I spent so much time explaining depth of field.
Turbulent Turtle
F-TR competitor
I thought I would provide a visual aid for this topic.
In the attached jpeg, I create a VERY SIMPLISTIC example to describe parallax. It applies to first and second focal plane reticles so I just created a focal plane for a reticle. I eliminated the erector assembly and the zoom lens for simplicity sake and just showed the "reticle focal plane." This is what the eyepiece focus adjustment sets up to your eye. This needs to be setup first and then locked down; you must never play with this adjustment in the field.
So the top diagram shows the target or objective in proper focus to the reticle focal plane and the merged image created "locks" the reticle to the target picture, they are both on the same plane.
In the bottom diagram, the target is not properly focused on the reticle focal plan though it may still appear clear enough because of the depth of field for that distance. Since the target is not focused properly on the reticle focal plane, in fact its focus is slightly past the reticle plane, the image presented to the eye does not have the reticle and the target locked on the same plane and if the eye moves side to side, or up and down, the image of the target will appear to move in front of the target, thus illustrating the parallax. problem. It's like holding out your finger at arm's length in front of your eye focused on an object behind it. If you move your head around while still focusing on the object, your finger will appear to move.
In the attached jpeg, I create a VERY SIMPLISTIC example to describe parallax. It applies to first and second focal plane reticles so I just created a focal plane for a reticle. I eliminated the erector assembly and the zoom lens for simplicity sake and just showed the "reticle focal plane." This is what the eyepiece focus adjustment sets up to your eye. This needs to be setup first and then locked down; you must never play with this adjustment in the field.
So the top diagram shows the target or objective in proper focus to the reticle focal plane and the merged image created "locks" the reticle to the target picture, they are both on the same plane.
In the bottom diagram, the target is not properly focused on the reticle focal plan though it may still appear clear enough because of the depth of field for that distance. Since the target is not focused properly on the reticle focal plane, in fact its focus is slightly past the reticle plane, the image presented to the eye does not have the reticle and the target locked on the same plane and if the eye moves side to side, or up and down, the image of the target will appear to move in front of the target, thus illustrating the parallax. problem. It's like holding out your finger at arm's length in front of your eye focused on an object behind it. If you move your head around while still focusing on the object, your finger will appear to move.
Attachments
Been reading this with interest. I have a 4x16/40 Bushnell 4200 with adjust objective, generally leave it set at 300 yd, seems fairly well in focus at other ranges. I have same scope with side parallax adjust. that seems to have to be adjusted (parallax) to be in focus at any different distance.(do not like this). Do you think this is because I may not have set my primary(eyepiece) focus correctly, or is this a characteristic of side para adjustment scopes?
Turbulent Turtle
F-TR competitor
An adjustable objective is the simplest and best way to adjust parallax in a riflescope. Your maximum magnification is low enough that the depth of field with the focus set at 300 yards is large enough and good enough to lead you to believe that everything is fine at any distance. That is incorrect, if you want to be sure there is no parallax involved you MUST focus the objective lens to the target distance.
I do not have the full technical details on how a side focus works in terms of equations and so forth but it is my belief that the added lens in the mechanism increases the degree of criticality in the fabrication of the scope. It could very well be that the amount of adjustment needed to effect a change is quite a bit smaller than with an adjustable objective, so a smaller change has a bigger effect.
So in answer to your question, if your reticle is (there's that word again,) crisp and clear in your eyepiece then just adjust the focus and be aware that a side focus is more finicky than an adjustable objective.
I do not have the full technical details on how a side focus works in terms of equations and so forth but it is my belief that the added lens in the mechanism increases the degree of criticality in the fabrication of the scope. It could very well be that the amount of adjustment needed to effect a change is quite a bit smaller than with an adjustable objective, so a smaller change has a bigger effect.
So in answer to your question, if your reticle is (there's that word again,) crisp and clear in your eyepiece then just adjust the focus and be aware that a side focus is more finicky than an adjustable objective.
Yeah, I was aware that it would not be parallax free just because it seemed focused at different distances, but it is at least focused good enough to use in hunting situations.(where you might not necessarily take or have time to mess with parallax adj). The side parallax is practically useless (focus wise) unless you make adjustments.The depth of field thing is probably the culprit, as you said internals are different.Thanks for your help/opinion.
Turbulent Turtle
F-TR competitor
Your question sent me searching the Internet and I came up with this link:
http://www.6mmbr.com/parallax.html
Imagine that. LOL.
Anyway, it talks about AO and SF and it has a diagram that you will recognize. I'm not sure if a reduced DoF field is real in a side focus scope compared to an AO. I have read some places that state that, but without formulas or attribution. The linked article above does mention the coarseness of the adjustment of the SF Vs the AO as an issue.
http://www.6mmbr.com/parallax.html
Imagine that. LOL.
Anyway, it talks about AO and SF and it has a diagram that you will recognize. I'm not sure if a reduced DoF field is real in a side focus scope compared to an AO. I have read some places that state that, but without formulas or attribution. The linked article above does mention the coarseness of the adjustment of the SF Vs the AO as an issue.
I have searched high and low, hoping to run across someone with the same observations. One would think if it were a characteristic of side focus scopes in general, it would be mentioned somewhere.(as much comparison and nitpicking goes on about optics)
I guess I will have to play with the focus a little and see if I notice anything changing. The only reason I ended up with it was at the time, I thought the adj obj 4200 had been discontinued when I wanted another.(I see a few old stock available again now, guess I ought to grab one.)
Very happy with them otherwise.
I guess I will have to play with the focus a little and see if I notice anything changing. The only reason I ended up with it was at the time, I thought the adj obj 4200 had been discontinued when I wanted another.(I see a few old stock available again now, guess I ought to grab one.)
Very happy with them otherwise.
Turbulent Turtle
F-TR competitor
I think that anyone who has a good amount of experience with AO and SF will agree that SF is more coarse in adjustment range and therefore more prone to showing what you have observed. I'm also inclined to postulate that the elements used in an SF are causing a reduction in DoF, but I just don't know for sure if that's even possible. The things that affect DoF are distance, magnification and aperture size; that's from my photography experience. I'm still learning about riflescopes.
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