Rifle Scopes Myth?: Variable power scopes have shifting zero

[SandLine]

I'm sure this is a noobie question but I'll ask anyway...

Is the zero on a variable power scope only good for the magnification level at which it was zeroed? i.e. if I zero the rifle on 22x, would it no longer be zeroed if I changed the magnification to 6x?

If this is the case, does anyone have an explanation for why this occurs?

 

[Pete E]

Re: Myth?: Variable power scopes have shifting zero

On any half decent variable, they should stay zeroed throught out the magnification range.

It wasn't always like that though, especially on cheap scopes with reticules in the second focal plane..

I'm not an optical engineer so can't really explain why it happened...

 

[SandLine]

Re: Myth?: Variable power scopes have shifting zer

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Pete E</div><div class="ubbcode-body">On any half decent variable, they should stay zeroed throught out the magnification range.
</div></div>

Good to know. So as long as I get a Leupold or something of greater quality, I should be fine? Even if the reticle is in the second focal plane?

 

[Lindy]

Re: Myth?: Variable power scopes have shifting zer

If you find a variable scope where the point of aim varies as the power ring is turned, send it in for repair - because it's broken - or just throw it away. No variable scope from a reputable manufacturer will do that.

 

[okiefired]

Re: Myth?: Variable power scopes have shifting zer

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">If you find a variable scope where the point of aim varies as the power ring is turned, send it in for repair - because it's broken - or just throw it away. No variable scope from a reputable manufacturer will do that.

</div></div>

Ditto.
You dont have to spend enough for a Leupy or better, there are many many scopes for less money that will hold zero throughout thier magnification range.

okie

 

[el gordo2]

Re: Myth?: Variable power scopes have shifting zer

Any scope made with the reticle in the 2nd plane can have a shift when going through the power range, doesnt matter if cost $50 or $1500.

Scopes with 1st reticles however will not shift while going through the different magnifications.

 

[Lindy]

Re: Myth?: Variable power scopes have shifting zer

I don't know where you got that idea, but it's incorrect. If that were the case, a scope with a SFP reticle would only have a valid zero at one magnification.

That's not the case. If you bag the rifle up good, and aim the reticle at a target, if the reticle shifts point of aim as you change the magnification, the scope is broken - or just crap.

 

[CoryT]

Re: Myth?: Variable power scopes have shifting zer

All SFP variable power scopes have some degree of shift, referred to as track-out error. In a good quality scope, the track-out error is so small that you can only see it in a comparator, you will never see it on a range while shooting. If the zoom group is poor quality or badly aligned, you can end up with a visible shift in POI, in which case, as Lindy says, it's either broken or crap.

FFP designs are not subject to track out, as the zoom group is only magnifying the image which already has the reticle in it.

 

[our gang]

Re: Myth?: Variable power scopes have shifting zer

The important thing about variables vs fixed is that varis have far more things to go wrong. A top quality fixed power scope can be had for the price of an average variable. As Finn was famous for saying: "If a big game animal is too far to shoot with a 3X scope he is too far."
By extension, a 10X should serve any reasonable sniping application.
Try a top quality fixed scope, you'll never go back.

The rifle is a 1935 R.F. Sedgley Springfield 400 Whelen, the scope is a Leupold Alaskan 2.5X, the range was 250 yards 45 minutes before dark. One 350 gr (old) X bullet. Tasty critter!

 

[LoneWolfUSMC]

Re: Myth?: Variable power scopes have shifting zer

Wow, that's a big boy. Good kill.

But yes to recap, a quality scope should not have enough error to be noticeable to the shooter or target.

The cheapest variable I have doesn't exhibit any track-out.

 

[Rob01]

Re: Myth?: Variable power scopes have shifting zer

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mr. Humble</div><div class="ubbcode-body">
Try a top quality fixed scope, you'll never go back.

</div></div>

Once you try a top quality variable you will never go back to a fixed. I know I never will.

 

[noname]

Re: Myth?: Variable power scopes have shifting zer

I'm probably reading the question wrong -- if sfp don't change impact, then why do we need ffp, and also why does rapid Z reticles raise the point of impact, when the power on the variable is decreased? this is also the case for Swaro on line ballistic program, and also why does the leupold BAS show a large trigangle for the flatter shooting rounds and a smaller triangle, (decreased power which raises the poi) on less flat traj. on their varmint scope reticle?

 

[Rob01]

Re: Myth?: Variable power scopes have shifting zer

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shooter2</div><div class="ubbcode-body">I'm probably reading the question wrong -- if sfp don't change impact, then why do we need ffp</div></div>

Because with FFP your mil or MOA reticle will subtend correctly on any power and not just one as on a SFP. This isn't a big deal to some but it is to others.

Don't know about the other reticles in your question as I don't use them.

 

[LoneWolfUSMC]

Re: Myth?: Variable power scopes have shifting zer

Rob explained it.

FFP is better for just about everything but target shooting. With Target shooting SFP is better because as you increase magnification the reticle obscures less of the target. Target shooting is also more of a static endeavor with known distances negating some of the benefits of FFP (like forgetting what power your scope is on or bumping the power selector ring).

 

[CoryT]

Re: Myth?: Variable power scopes have shifting zer

Besides, it's FFP reticles that don't have the issue of potential track out errors.

The ONLY disadvantage of an FFP reticle, if you want to call it that, is the apparent change in size as you zoom. If the retcle is too fine, it can be hard to see at a lower power. If it's too thick, at a high power it will appear to cover more of the target.

Given the quality of even inexpensive current variables, the only advantage to a fixed power scope is slightly smaller size and weight.

 

[our gang]

Re: Myth?: Variable power scopes have shifting zer

More reasons for fixed power, NO FFP, SFP issues.

 

[noname]

Re: Myth?: Variable power scopes have shifting zer

thats the point sfp scopes do change poi, with change in magnification, the greater the range the greater the change, the better the scope , the easier it is to see.
Larry-passed your place the other day on the way to Double Cabin you guys got a lot of water this winter.

 

[Lindy]

Re: Myth?: Variable power scopes have shifting zer

Attemp at proof by repeated assertion. Fail.

Proof by Repeated Assertion

<span style="font-weight: bold">Good</span> scopes do not change Point of Aim with magnification changes enough to affect the impact of the bullet.

If you have a bad SFP scope, ditch it. And it's easy to tell if you have a bad one - as I said, just bag the scope up, point it at a small target, and change the power through its range. If the center crossshairs move noticeably as you change the magnification, it's broken. Get it fixed or replace it.

You can also measure the magnitude of that change with an SFP scope if you want. Doing so requires an optical collimator, and a magnifying monocular is handy, to use behind the scope to make it easier to quantify small measurements through the scope.

Now, it's quite true that the values of a graduated reticle change as you change the magnification.

If that bothers you, that's a good reason for a FFP scope, which happens to be all that I currently own, because they are much better suited to tactical shooting than SFP scopes.

Those who only punch paper with plenty of time to dial elevation changes between shots may have no need for a FFP scope, though.

 

[ds]

Re: Myth?: Variable power scopes have shifting zer

Several years ago at IWA (Europe) I remember asking Meopta and Zeiss / Hensoldt reps about poi change with 2fp scopes through the magnification range. What I understood from that was that about 1/2 moa max shift is possible during extreme temperature changes - think about it, what you have is a lens group moving within the tube - there must be some play as otherwise it would not function. This play must be sufficent for the scope to function during both hot and cold extremes when the scope expands and contracts (I was interested in a temp range from +35c to -30c). During more normal and stable temperatures the poi change would be very small.

 

[kombar]

Re: Myth?: Variable power scopes have shifting zer

I have an old Blazer 6-24x on one of my cheap rifles. It has reticles in both the first and second focal planes. The FFP reticle is a little blade that you can raise and lower via a knob, to assist in zeroing the scope quickly. The normal aiming reticle is in the second focal plane, so any changes are easily seen by comparing the two.

The SFP reticle definitely shifts, but it's not even noticeable until you get up to roughly 18x. I'm not very sure you could observe the change by throwing the rifle on sandbags at the range and looking through it, since the extra movement of your hand making the adjustment would conceal the shift.

While it's difficult to say exactly how much this shift is, it appears to be around .55 MOA. This was measured with a USO spotter by comparing the two images against terrain features. Bear in mind that this is a lower quality scope.


And to the OP: <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Is the zero on a variable power scope only good for the magnification level at which it was zeroed? i.e. if I zero the rifle on 22x, would it no longer be zeroed if I changed the magnification to 6x?

If this is the case, does anyone have an explanation for why this occurs?</div></div>

In your example, going from maximum magnification to minimum, the reticle will "grow" and completely conceal the shift. On my cheap scope, it appears to work like any other backlash. The reticle will shift down and left whenever I dial down in magnification, and it will shift up and right whenever I dial it back up. The shift is always the same amount.

If it was a concern to you, you could always adjust to your desired magnification from the same direction and any shift will go away completely.