Optical centering

[buttloaves]

I was reading an article in one of the mags about centering your scope before fitting to your gun, i would have thought the cross hairs will finish up in the same place regardless of where they started from. I always just put it on and see where it is and adjust from there, never had any problems, any thoughts? Don't string me up..
The hirsute gent in the mag was sporting an impressive full set.
He should don a bretton cap, he'd look like captain haddock, no offence intended..

[Blackrider]

Haven't seen the article but I assume you mean "cranking" the turrets as far as they will go, then return, counting off each click until you reach the "far end" of the travel then winding backwards for half that total ?

Only ever done it once a few years back, never bothered since.

[gunstock]

If you are using target turrets a lot do it if not worry

[Gazzmondo]

I think the idea is that you centre the scope turrets as described then use shims between the scope and mounts to get a rough zero, so that you have the full range of adjustment available on the scope turrets.
Don't bother myself.

[thisisdonald]

The idea is that if the scope is optically centred you will get the clearest picture with maximum light transmission to your eye , bexause you will be looking at the crosshairs directly through the centreline of the scope - that is if you use adjustable mounts to zero your scope. Like most have said already, you can get by without it.
I always do it when i get a new or second hand scope or am putting a known good scope and mounts on a new gun.
The quickest way is to use a mirror in a bright room. Lay the mirror down. Turn mag to lowest setting. Put objective bell flat on the mirror and look through the eyebell from a distance that you can see two sets of crosshairs. Now just twiddle your knobs until the crosshairs are lined up with each other.
The reason i do this is so that if there is a problem with the scope or mounts or possibly even a bent barrel, it will show up clearly when you try to zero the gun, as you will have to make mega adjustments to get on zero.
If you go to the hassle of using plumb lines and bubbles to set up your scope, why wouldnt you spend 30 seconds optically centreing it before you start?

[Jonjon79]

Interesting post. Thanks for the info Donald - I've never had it explained like that before.

I've always done mine the same as the op.

[Tone]

I am all for setting up a scope properly, however, am i missing something?

If you start with your cross hairs in the centre when you mount the scope, and assuming you are not using adjustable mounts or shims, then to zero onto your point of impact you will have to adjust windage and elevation to get zero, so does it matter what your starting point is?

Centering a scope will tell you how close you are to maxing out but with target turrets you can see that anyway, and regardless, i am not a fan of adjustable mounts or shims so wouldn't use them anyway.....

[Geezer]

I do it for the same reason as Donald - it removes one variable from the diagnosis if you scope up and find the gun hitting way off the POA.

If you want a quick way, don't count the number of clicks, just the number of turns of each turret, then halve that. That will get you close enough to centre.

[Zero58]

I was reading an article in one of the mags about centering your scope before fitting to your gun, i would have thought the cross hairs will finish up in the same place regardless of where they started from. I always just put it on and see where it is and adjust from there, never had any problems, any thoughts? Don't string me up..
The hirsute gent in the mag was sporting an impressive full set.
He should don a bretton cap, he'd look like captain haddock, no offence intended..

As far as I can recall centre the scope to fall clicks left right up down will give you a square box you do this twice and at each full set of clicks you fire a shot so you should end up with pellet on pellet at each corner so I would say centring the scope is nothing more then a check to make sure scope is not broken and is performing corectly that's only my opinion....... not hard fact......

[thisisdonald]

I am all for setting up a scope properly, however, am i missing something?

If you start with your cross hairs in the centre when you mount the scope, and assuming you are not using adjustable mounts or shims, then to zero onto your point of impact you will have to adjust windage and elevation to get zero, so does it matter what your starting point is?

Centering a scope will tell you how close you are to maxing out but with target turrets you can see that anyway, and regardless, i am not a fan of adjustable mounts or shims so wouldn't use them anyway.....

If you think about light travelling through the scope, it is designed to transmit right through the centre. Now if your zero is say high and right toward the 1 oclock, really extremely due to a bent barrel or bad mounts, then your eye will be looking at the cross hairs high and right. Now if you take into consideration the quality of the scope, this could mean that you are not getting the clearest image.. even scopes priced over 100 pounds can be blurry at the edges on higher mag..

If you take these things into account, it starts to make sense to try and have your zero fall as close to the optical centre of the scope as possible.

NOW if you take into account all the years we just plonked scopes onto rifles and zeroed them without taking any special efforts to have scopes centred or straight, and had great fun in ignorant bliss, i guess it really doesnt matter unless it gets into your brain.. or you are a extreme long distance precision shooter

[Zero58]

If you think about light travelling through the scope, it is designed to transmit right through the centre. Now if your zero is say high and right toward the 1 oclock, really extremely due to a bent barrel or bad mounts, then your eye will be looking at the cross hairs high and right. Now if you take into consideration the quality of the scope, this could mean that you are not getting the clearest image.. even scopes priced over 100 pounds can be blurry at the edges on higher mag..

If you take these things into account, it starts to make sense to try and have your zero fall as close to the optical centre of the scope as possible.

NOW if you take into account all the years we just plonked scopes onto rifles and zeroed them without taking any special efforts to have scopes centred or straight, and had great fun in ignorant bliss, i guess it really doesnt matter unless it gets into your brain.. or you are a extreme long distance precision shooter

Total agree with you Donald other wise you will be hanging plumb lines every where and getting weird glint in the eyes after all not all rifles have scopes so get out there and have fun wonky scope and all

[essjay]

The idea is that if the scope is optically centred you will get the clearest picture with maximum light transmission to your eye , bexause you will be looking at the crosshairs directly through the centreline of the scope - that is if you use adjustable mounts to zero your scope. Like most have said already, you can get by without it.
I always do it when i get a new or second hand scope or am putting a known good scope and mounts on a new gun.
The quickest way is to use a mirror in a bright room. Lay the mirror down. Turn mag to lowest setting. Put objective bell flat on the mirror and look through the eyebell from a distance that you can see two sets of crosshairs. Now just twiddle your knobs until the crosshairs are lined up with each other.
The reason i do this is so that if there is a problem with the scope or mounts or possibly even a bent barrel, it will show up clearly when you try to zero the gun, as you will have to make mega adjustments to get on zero.
If you go to the hassle of using plumb lines and bubbles to set up your scope, why wouldnt you spend 30 seconds optically centreing it before you start?

There's no point in optically centreing a scope unless you are using adjustable mounts (or shims).
If you have a bent barrel, misaligned scope rails or problems with standard mounts, only adjustable mounts will work.
Otherwise you will experience cross-over and the scope can only be zeroed at one range.

[El Tel]

I tried the Mirror effect but could not see the image of the cross hairs in the mirror, the problem being it is a Leupold MK4 comp fixed 32 mag.

[thisisdonald]

There's no point in optically centreing a scope unless you are using adjustable mounts (or shims).
If you have a bent barrel, misaligned scope rails or problems with standard mounts, only adjustable mounts will work.
Otherwise you will experience cross-over and the scope can only be zeroed at one range.

True.. and if you don't know you have any of these problems, a a new gun or new mounts, then optically centering your scope should give you a good indicator that a problem exists.

I tried the Mirror effect but could not see the image of the cross hairs in the mirror, the problem being it is a Leupold MK4 comp fixed 32 mag.

It needs to be done at the lowest mag.. 32 is a wee touch high methinks!http://www.co2air.de/wbb3/index.php?...readid=54971:p

[Steyr]

It tells you how things are in relation to perfect alignment in the vertical and horizontal planes.

If you are having to make massive adjust up or down or left or right then it is telling you there is an issue.

OK.....livable for an air rifle but at 800 plus yards....your going to run into issues.

It could mean the breech block is out...the mounts are not true....there is a fault with the scope.....so much information and it is ignored.

In the USA the mount pins shaped like a pencil to see if the points touch and if they don't. ...they mill the scope rings till they do. Bit aggressive but it is an option.

Centering is useful knowledge not widely appreciated. Even a simple thing like turning a scope ring round could take it off centre or bring g it back......