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Parallax vs Focus

 
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  #36  
Old 01-22-2006, 01:36 PM
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Join Date: Dec 2001
Location: Lancaster,CA
Posts: 16
Re: Parallax vs Focus

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
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  #37  
Old 01-24-2006, 06:49 PM
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Re: Parallax vs Focus

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.
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  #38  
Old 01-27-2006, 11:32 AM
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Location: Lancaster,CA
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Re: Parallax vs Focus

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

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

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

thanks
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  #39  
Old 01-27-2006, 08:15 PM
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Re: Parallax vs Focus

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?
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  #40  
Old 01-28-2006, 10:26 AM
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Join Date: Dec 2001
Location: Lancaster,CA
Posts: 16
Re: Parallax vs Focus

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 [img]/ubbthreads/images/graemlins/smile.gif[/img]
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  #41  
Old 03-04-2006, 05:12 PM
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Join Date: Mar 2003
Location: Schofield, WI.
Posts: 323
Re: Parallax vs Focus

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
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  #42  
Old 03-05-2006, 06:55 AM
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Posts: 2,114
Re: Parallax vs Focus

[ 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.......
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