Adjustable objective

[jager]

Forgive my ignorance concerning this question.

What is the benefit of this if any?

The scope is a 4.5-14x44 Zeiss.

Thanks.

[mossback91]

helps paralax..........helps keep the crosshairs in the right position when you move slightly while aiming......sorry i suck at explainging stuff......I might have just made zero sense to you   

[bobcat]

You can adjust the scope for the distance you are shooting to eliminate parallax. Most scopes without an adjustable objective will have the parallax set for 150 yards, so that when shooting at any other distance, there will be parallax and it could affect accuracy. It apparently isn't significant enough to matter until you get up to 10x and more, which is why you don't see scopes such as the 3-9's available with an AO.

[jager]

So.....when a scope says adjustable parallax that is the same as adjustable objective?

Is it a focus or thickening of the crosshairs that is corrected?

I've never had a scope that was more than 10x.

[bobcat]

So.....when a scope says adjustable parallax that is the same as adjustable objective?

Yes.

Is it a focus or thickening of the crosshairs that is corrected?

No it has nothing to do with focus.




It's not easy to explain so I copied this from wikipedia:

Parallax problems result from the image from the objective not being coincident with the reticle. If the image is not coplanar with the reticle (that is the image of the objective is either in front of or behind the reticle), then putting your eye at different points behind the ocular causes the reticle crosshairs to appear to be at different points on the target. This optical effect causes parallax induced aiming errors that can make a telescopic sight user miss a small target at a distance for which the telescopic sight was not parallax adjusted.

To eliminate parallax induced aiming errors, telescopic sights can be equipped with a parallax compensation mechanism which basically consists of a movable optical element that enables the optical system to project the picture of objects at varying distances and the reticle crosshairs pictures together in exactly the same optical plane. There are two main methods to achieve this.

By making the objective lens of the telescopic sight adjustable so the telescopic sight can compensate parallax errors. These models are often called AO or A/O models, for adjustable objective.
By making an internal lens in the internal optical groups mounted somewhere in front of the reticle plane adjustable so the telescopic sight can compensate parallax errors. This method is technically more complicated to build, but generally more liked by parallax adjustable telescopic sight users—unlike AO models, which are read from the top, the sidewheel's setting can be read with minimal movement of the head. These models are often called side focus or sidewheel models[7].
Most telescopic sights lack parallax compensation because they can perform very acceptably without this refinement. Telescopic sights manufacturers adjust these scopes at a distance that best suits their intended usage. Typical standard factory parallax adjustment distances for hunting telescopic sights are 100 yd or 100 m to make them suited for hunting shots that rarely exceed 300 yd/m. Some target and military style telescopic sights without parallax compensation may be adjusted to be parallax free at ranges up to 300 yd/m to make them better suited for aiming at longer ranges[8]. Scopes for rimfires, shotguns, and muzzleloaders will have shorter parallax settings, commonly 50 yd/m[9] for rimfire scopes and 100 yd/m[10] for shotguns and muzzleloaders. Scopes for airguns are very often found with adjustable parallax, usually in the form of an adjustable objective, or AO. These may adjust down as far as 3 yards (2.74 m)[11].

[jager]

 

Thanks!

[mazama]

Set a target out at 500yds without AO, you will notice it moving as you move your head, without AO adjustment they set at about 200yds.