Parallax vs Focus

[hareng]

Sorry to disagree Bart i have seen 10's of different models and also had the misfortune to end up with one some years back. 5 1/2" of movement at 100 yards when in focus dependant upon where head/eye was placed.
This has nothing to do with pa/focus adjustment, you still get it when there is a bad one, usually asian build.
Never seen a decent Leup standard or modded suffer from this parallax. As long as the ret can be seen, you could move your head around and the zero will not change whether focused or not.
If scope is focused at another range it will not be as clear as it should, more than likelt blured and or will not be visible at all. So if pa/focus for clarity at every range ignoring what scope says, it is deemed correct for that distance, hence rangefinding a good bloke will get the range within 3% every time.

 

[Bart B]

Jonny, I understand why you've disagreed with what I said. I too, have looked through a few scopes that had parallax when the target image was focused very sharply. Here's how it happened.

In every instance, the scope's eyepiece was not focused properly on the reticule but instead either in front of it or in back of it. When the scope's front lens was turned/moved to focus a sharp image for the user, that image was in the same plane as the eyepiece was focused at. And yes, the reticule appeared to move relative to the target when the eye was moved around behind the scope. This is a common occurance.

Now here's the rest of the story. When the scope's eyepiece was correctly focused on the reticule, then the scope's front/objective lens was refocused for the sharpest image, the reticule no longer moved on the target as the eye moved around behind the scope.

It is opto-physically impossible for a scope sight to have its reticule appear to move relative to the target when the eye's moved around looking through the eyepiece when the target image and eyepiece are both properly focused on the reticule.

 

[Jon A]

I think I understand exactly what you're saying, Bart. When I first got my 4.5-14 LR, I did the old "look at the sky, look at a wall" focus for the eyepiece--just like the instructions say. I found at the range the first couple of times, when parallax was eliminated the crosshairs were blurry. When it was "focused" with the side wheel, it had parallax.

I came to the conclusion that the best way to focus the eyepiece was to first eliminate parallax while aiming at a target on the range. Then, focus the **** eyepiece until both the target and crosshairs are sharp. Does that sound like a good method to you?

 

[Guest]

O'kay, so I read all of this and it brings up one very important question for me since I just bought a Leupold VXIII 4.5-14x50 LR with the side "focus". Is it going to be a pain to get everything focused and shooting straight at coyotes inside of 400 yds? The vast majority of my shots are within 200 yards though. I just don't want to have to mess around with a bunch of focusing while I've got a coyote trying to get down-wind of me, and I also want to get good heart/lung shots. Will this be an issue for me? /ubbthreads/images/graemlins/confused.gif

Thanks,

Rusty

 

[Bart B]

Jon A, you should first focus the eyepiece such that your aiming eye gets perfect instant focus on the reticule. Our eyes nature is to automatically and instantly focus on what we're looking at. After the eyepiece is set correctly for your aiming eye, then move on to focusing the scope's front lens at the target's range. This is the best/only way to set up the scope for ones aiming eye.

Here's how to do it correctly:

1. Unlock, then back out (unscrew) the scope's eyepiece to where the reticule appears fuzzy or out of focus when you look through the scope for only 1 second.

2. Screw the eyepiece in one turn, then with both eyes, look at something about 100 yards away. While looking at that 100-yard point, move the scope quickly to your aiming eye then look through it for only 1 second, then put the scope down. If the reticule appeared fuzzy, screw the eyepiece in one more turn, then repeat this step. If the reticule starts appearing sharper, go on to step 3.

3. Screw the eyepiece in one-half turn, then with both eyes, look at something about 100 yards away. While looking at that 100-yard point, move the scope to your aiming eye then look through it for only 1 second, then put the scope down. If the reticule still appeared a little fuzzy, screw the eyepiece in one more half-turn, then repeat this step. When the reticule appears very sharp the instant you look through the scope, go on to step 4.

4. Lock the eyepiece in place. Don't ever move it unless your eyesight changes (new perscription for your glasses, etc.).

5. Put the scope in or on something that holds it still while you look through it at a target exactly 100 yards away (yes, measure off the distance to do it). Set the scope's focus for 100 yards (if marked, otherwise use your best guess).

6. Look through the scope with the reticule on the target then move your eye around and look for relative movement between the reticule and target. If the reticule doesn't stay on the target, change the scope focus a small amount then retest. Repeat this step until moving your eye around looking through the stationary scope shows no relative movement between the target and reticule. Then go on to step 7.

7. Note where the 100-yard mark on the objective lens focus is relative to the index mark. Make a new index mark at the 100-yard line. This is your particular scope's new index mark. Cover up the old one with something. When you set the scope's infinity setting at this new index mark, the scope will be focused pretty close to infinity. And setting any other range mark to this new index should result in zero parallax at that range.

 

[Bart B]

Rusty, focus your scope such that it's parallax-free or focused at about 150 yards. It'll be just fine for targets up to 400 yards.

 

[Guest]

Thanks Bart....I was getting nervous. This board is priceless. I've learned more in just a few days of lurking than I have in years of actively posting on other boards.

Thanks, guys!

Take care and God Bless,

Rusty

 

[sheephunter]

Bart,

I have been ruminating and trying to make the best of this situation for years.
Maybe you can direct me to what I have to live with.

Given the fact that all my scopes dont have seperate adjustment for paralax and focus.

I believe - correct me if wrong ) that the only adjustment in the rear of the scope is meant to adjust the focus for a certain distance.
Of course ,doing so, I mess up,when I adjusted the paralax before, using - yes- the same ring

Reading up, I think these scopes are supposed to have an "inborn" paralax for the "convential distances, but not necessarily aged eye?

Anyway,best as I can do is adjust for focus at selected distance and live with the paralax


to complicate, Of course I have a "magnification" ring / adjustment too

thanks for your suggestions

 

[Bart B]

Sheephunter, rifle scopes work as follows....

The rear lens (eyepiece) only adjusts so the reticule appears sharp and clear to the user. It does not do anything to focus the scope on the target. It works exactly the same way a magnifying glass does so you can see a fine line on a sheet of paper with it. Make a '+' on a sheet of paper and look at it with a magnifying glass and you'll see and hopefully understand. Unless your vision changes, the magnifying glass will always need to be the same distance from the paper to see the + clear and sharp.

Does this make sense to you? You need to understand this before I go further in explaining anything else.

 

[sheephunter]

Thanks Bart,
No problems with your explanation.In practice then , one uses the rear ring adjustent to "focus" the reticle.

Now, tiem to proceed /ubbthreads/images/graemlins/smile.gif

How do you propose to focus on the target at distance x?

thanks

 

[Bart B]

OK, Sheephunter. Next is focusing on the target.

If you take that piece of paper with the '+' drawn on one side then use a low power magnifying glass to focus a bright image (such as a lamp or light bulb in your house) on the side opposite the +, this is how the objective lens works. Focusing your rifle scope's front lens does the very same thing.

When your scope's front lens focuses a distant target on the reticule, your eye is focused on the reticule from the back. This is how a scope works.

To focus your scope on a distant target, rest the scope on something so it points at something exactly 100 yards away. Then without touching the scope, look through it and move your aiming eye around. If the reticule appears to move around the aiming point, your scope is not focused at 100 yards. This is parallax; the scope's front lens is not focused to the same range as the target.

Change the front lens focus a bit, then look through it again moving your aiming eye around.

If there's more reticule movement than before, you moved the front lens focus the wrong way; move it back the other way past the point where it was to start with.

If there's less reticule movement than before, you've moved the focus in the correct direction but need to move it some more.

Refine the focus adjustment so there is no reticule movement about the 100-yard target when you move your eye around looking through the scope. When this is done, your scope is focused properly for 100 yards.

How's this sound? Think you got it now?

 

[sheephunter]

Bart,
thanks for your patience in your treatise , "scopes for idiots" , well and simple.
If I had a front lens adjustment I probably would have done what you explained,but I think I stated: I dont have the front lense adjustment.

just a rear lens adjustment and a manification ring for the variable scope power.

Thanks anyhow,it was worth a try /ubbthreads/images/graemlins/smile.gif

 

[jcpython357]

Guys, I was directed back to this thread from 24hourcampfire due to a thread I started this morning in which I told the guys there that I thought the eyepiece was for focusing the reticle. Now I'm a f__king idiot cuz I don't know how to focus a scope, so how can I say anything about any scope since I don't know nothing.

This all started when I was Gander and told the salesman a Leupold 2x20 pistol scope was a bit blurry compared to a Burris in a past comparison just last week, he then showed me how to focus it by turning the ocular out. Sure enough, it cleared up. But the reticle was dancing all over the place and the power seemed to increase a bit. When I turned my Burris 1.5-6 Sig. eyepiece (in) this morning it sure enough was out of focus, 12 CCW turns out and it was good to go again. It wasn't as noticable with a 3-9 FF when I did the same thing.

Sheephunter, rifle scopes work as follows....

The rear lens (eyepiece) only adjusts so the reticule appears sharp and clear to the user. It does not do anything to focus the scope on the target. It works exactly the same way a magnifying glass does so you can see a fine line on a sheet of paper with it. Make a '+' on a sheet of paper and look at it with a magnifying glass and you'll see and hopefully understand. Unless your vision changes, the magnifying glass will always need to be the same distance from the paper to see the + clear and sharp.

Does this make sense to you? You need to understand this before I go further in explaining anything else.


So, please tell me why did the 2x20 Leupold and my 1.5-6 Sig. become clear when I turn out on the eyepiece. This is getting confusing. Thanks, Jay

 

[Bart B]

[ QUOTE ]
So, please tell me why did the 2x20 Leupold and my 1.5-6 Sig. become clear when I turn out on the eyepiece. This is getting confusing.

[/ QUOTE ]
If the target image became sharp and clear when you backed out the eyepiece, that happened because the objective lens was focusing the target image well behind the reticule. The eyepiece lens has to be a fixed distance behind the target image formed by the objective lens. That distance is determined by your eye and glasses if you wear them.

If the target was at a very close range its image may well have been focused quite a ways behind the reticule. That's why you had to unscrew the eyepiece quite a bit to get it focused sharply on the target image.

Here's another way to look at it. Imagine a slide projector focusing a picture on a screen. This is what the objective (front) lens on a rifle scope does. Now take a magic marker and draw a large + on the screen; that + represents the scope's reticule. Take a pair of binoculars and look at the projection screen through them while sitting by the projector; you'll have to focus the binoculars to see the image as well as the retiule; this is what the eyepiece does. Now if you focus the projector so it makes a sharp image in front of or behind the projection screen, the image on the screen won't be sharp any longer. In order to see the image at its new position sharp and clear, you have to change the focus on the binoculars. So you refocus the binoculars and the image is sharp again but the + is no longer sharp 'cause it's not where the image is focused.

Hope this helps.......