I've been working on the range with a 2011 Leupold VXIII 3.5 x 10 40mm, no AO. It has minimal vertical parallax, but quite a lot horizontal. Why? Is this common? I've never noticed this before. It seems illogical to me.

What method have you used to measure the parallax? And at what distance?

100 yards/ The rifle was set firmly on the rests at the range and I simply moved my eye/head. The vertical was about 2", horizontal was about 4", as observed on the target. Leupold says this scope is focused for 150 yards. (fixed focus)

I did not install the scope, don't know if it is properly centered. I guess I should check. Could the problem be because the inner tube is aligned vertically but not horizontally?

Correct me if I'm wrong, but I believe that scope, as well as the newer VX3, is parallax free at 150yds. That is not where the scope is focused, as you can set that with the eyepiece. Not trying to insult your intelligence, but if you'll point the scope up at the sky and turn the eyepiece to get the reticle razor sharp. Then aim the scope at a 150-200 yd target and try to get the image as sharp as possible, while maintaining a sharp reticle. You will get the most/best image from your scope by doing this. I have several of the VX3 3.5-10x40 CDS scopes, and have no parallax issues when I set them up this way.

Hope that helps.

JG,
I've focused the eyepiece. Reticle is sharp. In any case, parallax is caused by the light rays from the objective lens not meeting the second lens, which is located in the erector tube, at the right distance. I called Leupold tech and they said it shouldn't make a difference at 100 yards. Kinda blew me off and didn't answer the question.

I have two of these VX3 3.5 x 10 scopes, and have no problem with them, even without AO. They are one of L's best scopes, used in the past by US military for sniper applications, so I'm befuddled.

Parallax is essentially an optical illusion. Parallax presents itself as the apparent movement of the reticle, in relation to the target, when your eye moves off center of the sight picture (exit pupil) or in more extreme cases it appears as an out of focus image. It indicates that the scope is either out of focus or more specifically the image of the target is not occurring on the same focal plane as the reticle. Maximum parallax occurs when your eye is at the very edge of the sight picture (exit pupil). Even when parallax is adjusted for a designated distance, there is an inadvertent error at other distances. Most brands of scopes that do not have a parallax adjustment are pre-set at the factory to be parallax free at or around 100 yards; rim fire and shotgun scopes are set at or around 50 yards. Most scopes of 11x or more have a parallax adjustment because parallax worsens at higher magnifications. Generally speaking parallax adjustment is not required for hunting situations and is primarily a feature used and desired by target shooters. A 4x hunting scope focused for 150 yards has a maximum error of only 8/10ths of an inch at 500 yards. At short distances, the parallax effect does not affect accuracy. Using the same 4x scope at 100 yards, the maximum error is less than 2/10ths of an inch. It is also good to remember that, as long you are sighting straight through the middle of the scope, or close to it, parallax will have virtually no effect on accuracy in a hunting situation.

The parallax you believe you have observed is well in excess of what is theoretically possible at 100 yards with a scope which is parallax corrected to 150 yards. I'd suggest that you (and a second person) check it again and if you find results that are similar to your first experience then you should send the scope to Leupold with a note telling them what you have found and asking that they rectify the problem. It won't cost anything and service is usually pretty quick.

Understanding Parallax with Leupold

We used to be told that a scope to be parallax-free at 100 to 150 yards would be free of parallax beyond that point. What our friend in the video does not mention is the close-range parallax. As he indicates, it really should not worry big-game hunters too much but I can recall a couple of pronounced examples where it could easily let you miss a rabbit's head at 60 yards.

The so-called classic stock is probably the biggest worry these days if it does not support your face consistently when lining up your brave new scope with the astronomical power range and 50mm objective.

I like the dude's saying that we don't need to dial a side adjustment knob to the real-and-measured distance but just until it is focused on the target.

Though the knob numbers don't correspond with known range distances in my Nikon Monarch 4-16, I wonder if calibrating them at a particular reticle focus could give you an ersatz range finder.

With a non AO leuppld, you can easily change the parallax setting yourself......

http://www.24hourcampfire.com/...ourself#Post10484822

Good stuff. Thanks for the useful info. Yes, cheekweld is important in controlling parallax. So is avoiding those toilet seat-sized objective lenses.

The bit about changing focus on non-AO scopes (JGRaider) was surprising. Who da' thunk?

I realize that for hunting parallax is seldom an issue if the shooter's eye is reasonably close to the scope centerline. For load development that small loss in accuracy can create difficulties.