collapse

Advertisement


Author Topic: That 3rd knob on the left side of your scope is not a "focus knob"  (Read 4034 times)

Offline KFhunter

  • Non-Hunting Topics
  • Trade Count: (0)
  • Legend
  • ******
  • Join Date: Jan 2011
  • Posts: 34514
  • Location: NE Corner
A gun guy showed me their scope, he had a butler creek scope cover blocking the focus ring, when I told him he might not like spinning that cap around focusing in, he said the 3rd knob was for focus.  I've heard this before, too many times.

parallax is kinda hard to explain, but if your focused in on something on a higher power zoom scope (especially cheap scopes) and if you move your eye a little bit to one side and the target moves around on the crosshairs a bit then you have it.  It's not the crosshair actually moving, it's the focus plane.

The knob will change the plane of focus so your target doesn't move around in the scope when you look at it, even if you move your eye a slight amount looking through a different part of the glass.  I guess it's possible to look exactly down the middle of your scope and not have parallax affect you even when present, but who can always look perfectly down the center of the scope in the field?  Not me.

It would be a good idea to get a cheap high power scope and practice recognizing parallax, and correcting it. 
« Last Edit: January 26, 2018, 07:05:57 PM by KFhunter »

Offline BULLBLASTER

  • Non-Hunting Topics
  • Trade Count: (+14)
  • Old Salt
  • ******
  • Join Date: Oct 2008
  • Posts: 8057
You shouldn’t have to set the focus for each soon power. Just once to your eyes.

Offline KFhunter

  • Non-Hunting Topics
  • Trade Count: (0)
  • Legend
  • ******
  • Join Date: Jan 2011
  • Posts: 34514
  • Location: NE Corner
You shouldn’t have to set the focus for each soon power. Just once to your eyes.

I reworded it, thanks for the correction.  I focus a lot due to contacts, glasses or no eyewear at all.  Normally when hunting I'll pop in some contacts to crisp things up, but don't always have them in then I'm a bit nearsighted.  I don't like the butler creek caps for this reason, or any caps that cover that focus ring. 

Point of this thread is to discuss parallax, I found a nice article on it.

http://blog.cheaperthandirt.com/understanding-and-correcting-parallax/
« Last Edit: January 26, 2018, 07:09:44 PM by KFhunter »

Offline Magnum_Willys

  • Political & Covid-19 Topics
  • Trade Count: (+1)
  • Old Salt
  • ******
  • Join Date: Nov 2009
  • Posts: 5437
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #3 on: January 26, 2018, 07:09:06 PM »
Yup - eye piece is for focus.  Left knob is parallax - move your head up and down as you move knob and parallax is set when aim point stops moving - just have to try it to see.  Very important for long range shooting.  Once set you should be able to focus with parallax knob from then on on a good scope to set parallax. 

Offline BULLBLASTER

  • Non-Hunting Topics
  • Trade Count: (+14)
  • Old Salt
  • ******
  • Join Date: Oct 2008
  • Posts: 8057
You shouldn’t have to set the focus for each soon power. Just once to your eyes.

I reworded it, thanks for the correction.  I focus a lot due to contacts, glasses or no eyewear at all.  Normally when hunting I'll pop in some contacts to crisp things up, but don't always have them in then I'm a bit nearsighted.  I don't like the butler creek caps for this reason, or any caps that cover that focus ring. 

Point of this thread is to discuss parallax, I found a nice article on it.

http://blog.cheaperthandirt.com/understanding-and-correcting-parallax/
I hadn’t even thought about guys with glasses or contacts or not using them
Luckily I don’t need corrective lenses for most things.  Makes sense

I usually close my eyes and slam the trigger

Offline Magnum_Willys

  • Political & Covid-19 Topics
  • Trade Count: (+1)
  • Old Salt
  • ******
  • Join Date: Nov 2009
  • Posts: 5437
You shouldn’t have to set the focus for each soon power. Just once to your eyes.
Eye piece focus you mean not scope focus -  My leupold scopes are out of focus until parallax is set.  I.e. in focus at 100 yards and 9 power is way out of focus at 500 yards and 24 power.  Will be brought into “focus” with parallax knob (assuming eyepiece adjusted - once - properly).

Offline Bofire

  • Political & Covid-19 Topics
  • Trade Count: (+5)
  • Old Salt
  • ******
  • Join Date: Oct 2007
  • Posts: 5524
  • Location: Yelm
  • Harley YAR YAR YAR!
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #6 on: January 26, 2018, 08:38:26 PM »
The real science of it is one thing, BUT the thing is it LOOKS more in focus , more clear, when I use it, to a degree. Mostly when shooting paper. However I shoot better paper groups with it, so for what ever reason if it works, it works. :chuckle: I do wear glasses.

Carl
When the chips are down..... the buffalo is empty!!

I do not shop at Amazon

Offline BULLBLASTER

  • Non-Hunting Topics
  • Trade Count: (+14)
  • Old Salt
  • ******
  • Join Date: Oct 2008
  • Posts: 8057
You shouldn’t have to set the focus for each soon power. Just once to your eyes.
Eye piece focus you mean not scope focus -  My leupold scopes are out of focus until parallax is set.  I.e. in focus at 100 yards and 9 power is way out of focus at 500 yards and 24 power.  Will be brought into “focus” with parallax knob (assuming eyepiece adjusted - once - properly).
Right. It brings the reticle and target both into focus.

Offline CP

  • Trade Count: (+6)
  • Old Salt
  • ******
  • Join Date: Mar 2008
  • Posts: 6453
  • Location: Mukilteo
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #8 on: January 27, 2018, 09:10:24 AM »
The eye piece adjust is to focus on the reticle.  I'm farsighted and a sharp, clear reticle usually means a fuzzy, out of focus target, especially at close range.  Reticle focus changes with glasses on or glasses off.

And yes, sometimes I use the parallax knob to focus on the target.  May not be what it's for but that works for my aging eyes.

Whatever works best for you, all eyes are not the same.


Offline jasnt

  • ELR junkie
  • Political & Covid-19 Topics
  • Trade Count: (+5)
  • Old Salt
  • ******
  • Join Date: Feb 2010
  • Posts: 6445
  • Location: deer park
  • Out shooting
  • Groups: WSTA
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #9 on: March 18, 2018, 08:43:02 PM »
What is Parallax?
By Earl Hines, Best of the West Master Gunsmith

When we talk about the accuracy of a shooting system, there is one element that most people know little about, don't understand, don't know how to apply, or don't recognize. Many people have indicated that they understand it but when asked, they give an inaccurate response. What I am referring to is that thing called parallax. What is it? How does it work? How do I adjust it? Is it important? How do I know when it's correct? And where do I start? All important questions. I will try to answer all these and more.

First, what is parallax? Parallax is having both the cross hairs and the target in the same focal plane so that no matter where your eye looks through the rear lens, the cross hairs do not change position on the target. How can that be accomplished? Well, modern scope manufacturers provide us with an adjustment mechanism on the opposite side of the right and left windage adjuster. Older scopes without this adjustable feature were parallaxed at a given distance. Depending on the manufacturer, they would parallax their scope between approximately 75 yards to 150 yards. At normal hunting ranges of the time, maximum of 3 or 4 hundred yards, the small amount of parallax was minimal (but still there).



Let’s look at understanding the concept of parallax. Look at the simple drawing in figure 1. In the center of the scope we have a cross, representing the reticle or cross hair inside your scope. On the left we have the part of the scope you look through, and on the right is our target. This being a simple drawing, we have no internal lenses or way to adjust for anything. If my position on the stock causes me to be absolute centered, then I would see along line “A” through the scope. If, for some reason my position causes me to look through the bottom portion of the scope I would see my cross hair on the upper part of the target, line “B”. That would be exactly opposite if I looked through the top of the scope, my cross hair would appear to be on the bottom of the target, line “C”.



So as you can see, by looking through the scope in different positions the cross hair would appear in different locations on the target. Now to apply this to shooting this simple system on a rifle, you can also see that if you were exactly in the center for 5 shots with a perfect rifle, your group would be acceptable and in the center of the target. Look at figure 2. Same rifle but this time your eye is at the bottom line “B”, and you fired 5 shots, again your group would be acceptable but at the bottom of the target because you would see the cross hair at the top of the target and compensate by moving your rifle cross hairs into the center of the target. Same for position “C”. But if you are not in the same position or on the same line every time, as illustrated in figure 2, your group would be much larger and you would be wondering where your accuracy was. That is why modern scopes have parallax adjustment capabilities.



When correctly adjusted, the internal workings of the scope will be able to focus both the target and cross hairs at the same time (on the same focal plane) without movement no matter where your eye is located. This would be correct parallax. Look at figure 3. Most scopes have this adjustable knob on the left side or your scope. There are numbers, varying anywhere from 25 ft. to the lazy 8, indicating infinity. These are “not” and I repeat “not” exact ranges that you can rely on to be accurate. They are approximations. So now you must focus the rear ocular (the lens that you look through to see the target) so that these numbers are close to the distance you want the parallax to be “free”. The term used when your scope is adjusted free of error or movement.



Start with your brand new scope. Turn the parallax knob to the lazy 8 position. Now go outside, with a clear blue sky preferably, point your scope towards the sky and turn your rear eye piece clockwise until it stops. Next, while looking through your scope, turn the ring counter clockwise. Turn the ring until the cross hair becomes crystal clear. Go slightly past this point and then back to insure that it is at the clearest point. At that point your scope is now adjusted to you and only you. The cross hair, being in focus, has been adjusted for your vision requirements to be correct for you. Now you can mount your scope on your highly accurate rifle and head to your favorite shooting spot and finish adjusting things.

If you are sighting in at 200 yards you need to secure your rifle on a bench using sand bags or a very steady bench rest and adjust your parallax knob to 200 yard setting. Position your rifle so that it is pointing at the center of the target when you let go of it. Now without touching your rifle, position your eye at a point so that you are looking through the very center part of the scope. This would be line “A” in figure 1. Now move your eye, not the rifle, up and down, side to side and 45 degrees in all directions. If the cross hairs move in the opposite direction on the target from your eye position, you are “out” of adjustment. To correct or to verify that you are in adjustment, turn the parallax knob either clockwise or counterclockwise a little. This does not take a great amount of adjustment. The cross hair will stop moving if you were out of parallax, or have greater movement if you were already in correct adjustment. The thing that you are looking for is no movement of the cross hair on the target.

If you have a rifle capable of shooting 1 inch groups at 200 yards, even with the most expensive scope in the world, your group size and consistency cannot be realized until your scope is adjusted for you and you understand parallax and adjust for it. Is parallax important? You bet ya. Your bullets will not go where you want them to until you have perfect parallax.

It is all very simple once you have seen improperly adjusted parallax and a parallax free scope setting. Remember, your rifle can shoot no more accurately than your parallax capabilities.
Just a thought for you. How many rifles have been taken to a gunsmith because the rifle “would not group”? You can bet many rebarrels, bedding jobs and such have been sold or charged for that only need parallax adjustment.
https://www.howlforwildlife.org/take_action  It takes 10 seconds and it’s free. To easy to make an excuse not to make your voice heard!!!!!!

The commission shall attempt to maximize the public recreational game fishing and hunting opportunities of all citizens, including juvenile, disabled, and senior citizens.
https://apps.leg.wa.gov/RCW/default.aspx?cite=77.04.012

Offline PastorJoel

  • Non-Hunting Topics
  • Trade Count: (+4)
  • Longhunter
  • *****
  • Join Date: Nov 2015
  • Posts: 881
  • Location: Bremerton
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #10 on: March 18, 2018, 09:07:19 PM »
I got a vortex viper with a "we're sorry" discount from Cabela's after they messed up my orders but I hadn't played much with the parallax until a few days ago at the range.  It has distances marked on the dial but they are WAY off.  75 on the dial is actually 100 and 110 on the dial is actually 200.  I wrote vortex and they basically said to ignore the numbers on the knob.

I say this not to complain but to educate other scope users that those numbers that are supposed to be the yardage may or may not be accurate.  It can be hard to test for parallax without a bench and so I am going to put new, accurate, numbers on my dial (on blue tape) so that when I know my distance I can dial it in.

Offline Calvin Rayborn

  • Trade Count: (+1)
  • Sourdough
  • *****
  • Join Date: Oct 2013
  • Posts: 1383
  • Location: Columbia Basin
  • Groups: NRA Life Member, ATA Gold-Card Life Member
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #11 on: March 18, 2018, 09:15:10 PM »
Parallax, my friend, Parallax...

Offline Bob33

  • Global Moderator
  • Trade Count: (+2)
  • Legend
  • *****
  • Join Date: Apr 2009
  • Posts: 21190
  • Groups: SCI, RMEF, NRA, Hunter Education
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #12 on: March 18, 2018, 09:18:20 PM »
I got a vortex viper with a "we're sorry" discount from Cabela's after they messed up my orders but I hadn't played much with the parallax until a few days ago at the range.  It has distances marked on the dial but they are WAY off.  75 on the dial is actually 100 and 110 on the dial is actually 200.  I wrote vortex and they basically said to ignore the numbers on the knob.

I say this not to complain but to educate other scope users that those numbers that are supposed to be the yardage may or may not be accurate.  It can be hard to test for parallax without a bench and so I am going to put new, accurate, numbers on my dial (on blue tape) so that when I know my distance I can dial it in.
I've never seen them to be accurate. From the article above:

"Most scopes have this adjustable knob on the left side or your scope. There are numbers, varying anywhere from 25 ft. to the lazy 8, indicating infinity. These are “not” and I repeat “not” exact ranges that you can rely on to be accurate. They are approximations. "
Nature. It's cheaper than therapy.

Offline dreamunelk

  • Political & Covid-19 Topics
  • Trade Count: (0)
  • Sourdough
  • *****
  • Join Date: Jan 2009
  • Posts: 2049
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #13 on: March 18, 2018, 09:26:55 PM »
Everyone eyes are a little different.  Adjust while you are looking through the scope and ignore the numbers.

Offline jasnt

  • ELR junkie
  • Political & Covid-19 Topics
  • Trade Count: (+5)
  • Old Salt
  • ******
  • Join Date: Feb 2010
  • Posts: 6445
  • Location: deer park
  • Out shooting
  • Groups: WSTA
Re: That 3rd knob on the left side of your scope is not a "focus knob"
« Reply #14 on: March 19, 2018, 05:58:36 AM »
Yup never seen a scope where the numbers line up with yardage.

 
Everyone eyes are a little different.  Adjust while you are looking through the scope and ignore the numbers.
eyes being different has nothing to do with parallax. Like said its not focus. It's the cross hairs being in the same plane as the sight pic. You could set it for 100 yards. Hand it to me and after I set the  opiture it should be parallax free
https://www.howlforwildlife.org/take_action  It takes 10 seconds and it’s free. To easy to make an excuse not to make your voice heard!!!!!!

The commission shall attempt to maximize the public recreational game fishing and hunting opportunities of all citizens, including juvenile, disabled, and senior citizens.
https://apps.leg.wa.gov/RCW/default.aspx?cite=77.04.012

 


* Advertisement

* Recent Topics

SimplePortal 2.3.7 © 2008-2024, SimplePortal