Focus dial or Parallax dial? (Ted ?!)

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travels4 fun,
In your post you state that target focus is set at 60 yards for rim fire as that is close enough for that cartrage. I think air rifle also works in this range. Thats all I ment that an air rifle dosen't need the ability to adust its focus on target for the ranges it will be used at. But thanks again for your posts and clearing up the meaning of parallax. That was really very helpfull and greatly appreicated.
 
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Thank you for a better explanation of what I meant to say. That is in fact how I set mine scope up. With a ever so slight pull back of my head I can see the ring and in proper position only if my eye is not perfect in the center. A scope that is set back to far gives to much room for the eye alignment to be incorrect and the shooter not knowing it.
 
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FOCUS or PARALLAX ?

Short, quick answer

FOCUS.

Parallax does not actually exist within the realms of rifle scope / telescope optics and Parallax 'Error' does not exist. (Full Stop / Period). The term parallax error applies to a certain rare situation within the highly specialized & critical world of camera optics - increasingly rare these days anyway.

Dont get me wrong here, Parallax exists as a phenomenon (in fact our cave dwelling forebears will have noticed it!*) but it doesn't exist within the body of the scope/telescope, its purely a function of 1 of 3 factors moving out of alignment to quite a gross degree - barring very crummy threading of an AO mech., that leaves the Human Eyeball Mk 1.

In 'pure' Optics our scopes consist of a stacked series of lenses (which are referred to as planes) for one of these planes to go off axis sufficiently for the human eye to notice, or make for more than a fraction of a Mill-radian at 1000 metres, requires serious incompetence from the maker of that scope. (I have seen the possible 'Friday Afternoon' scope or dodgy quick-fix Dedicated NV sight where the front lens wandered around, but in the first case it was production issue). This is all purely WITHIN the scope body itself.

Parallax 'Error' in the world we live in is HUMAN ERROR, Parallax is just Mathematics (its not either Naughty or Mischievous - unlike us Humans).

For a scope to function correctly at differing ranges/distances (distances to the Object of view or target) the Focal Plane Lens is required to move either forward or back to bring that Object image into the sharpest focus on the area/plane the users' eye is already focussing upon within the scope, the reticle, (if you've set the scope up correctly). The statement 'Focal Plane Lens' might give the alert reader a clue here !!
Assuming the other 2 elements have stayed exactly in position when the Focal Lens is moved all will be well. (& lets discount the theory the the reticle is composed of some amorphous, moving group of atoms!).

So, what could possibly go wrong ???

:)

Its the good old "Dumkopf Factor" - either the first stage of setting-up your scope to YOUR EYES, the Ocular Adjustment, has not been done correctly (Eye to Reticle adjustment), Or the Object (target at distance, whatever) is not completely focussed upon the reticle plane, or, most likely, YOU'VE MOVED YOUR HEAD !!

So, what are people on about ???

The scope makers who quote phrases like "Parallaxes down to", Parallax Adjustment Knob" or "our factory can Re-Parallax your scope to..." are talking drivel and a few have been at it for years. Sadly (to me) this has been taken-up by a few amongst us in the shooting world for whom the term Parallax has now become interchangeable with Range (or distance) or inconsistent head position. IT ISN'T EITHER, NEVER WAS and its sloppy thinking.

Scope makers, however august, are commercial enterprises - they seek to sell stuff, buddy !


* Parallax for juniors :) (OH! & cavemen - how are ya doin buddy?)
close one eye then line up a finger tip with an object about 5-6 feet away, keeping your finger & head still, close that one eye and open the other - its not pointing in the same place !!

 
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I am obviously late to this discussion, but I think that travels4fun and others have done a fantastic job of explaining it. Parallax adjustment is to remove error - The goal is not to achieve focus, but to eliminate any movement of the reticle with respect to different head positions. And this is why you see shooters moving the head while they adjust the parallax - they are looking for that perfect adjustment spot when parallax error has been eliminated. You can see me do this and several videos. I think the marauder .25 and Huntsman .22 review videos both show this. 

Fine tuning reticle focus should be done using the ocular dial. 
 
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Parallax ‘Error’ in the world we live in is HUMAN ERROR, Parallax is just Mathematics.

In fact very Pure Mathematics (sub-branch, Geometry, sub-sub branch Optics ).

Please dont anyone believe that untouched, unmoved scope reticles 'move'. (this way, madness lies)

'17 Bullets' comments about establishing a regime for Correct Head/Eye Position are entirely right.

Strangely or funnily enough those old Sniper scopes or Small Varmint scopes THE OLD BOYS USED with the very long, very narrow bodies & small OD Objective Lenses were NEVER accused of the dreaded 'Parallax Error' - I'm referring to the old scopes that traversed 2/3 length of ones' rifle, were adjusted for aim via their mounts and had tiny Ocular lenses which forced the user into a set head position. That type of riflescope operated in the 20-40 X range (if anyone thinks there were 'pathetic').


 
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