Parallax adjustment with a side focus

VIDEO

Traditionally, rifle scopes had a fixed parallax set at 100 meters or 100 yards; however, with the advance of shooting sports, such an approach was not adequate anymore. Scopes with fixed parallax offered the best resolution only at one distance (100 meters/yards) at which the target was in focus. At all other distances, the picture was less sharp or even blurry. An even bigger problem with this type of scope was the fact that, when shooting at the target, not at the same distance as the scope parallax setting, the shooter had to be very careful about his eye alignment with the optical axis. If the eye is moved away from the optical axis, the reticle on the target will move, which will worsen the accuracy. Since these errors are small, the fixed parallax option is still considered accurate enough for traditional hunting. For sport shooting, though, such small error leads to poor results. Parallax errors become more pronounced with magnifications higher than 12x, and that means the majority of scopes with magnification range under this value need no parallax adjustment.

With the ability of parallax adjustment, the accuracy of the riflescope is greatly enhanced at all distances. The shooter, however, has to adjust the parallax setting before making the first shot. Such scopes usually have AO – Adjustable Objective or SF – Side focus acronym in their name.

With SF – Side focus scopes, parallax is adjusted with a rotation of the turret on left side of the main tube. Such an approach offers easy adjustment of the parallax in the prone position and is the best solution for situations when parallax must be adjusted often. Due to this reason, such scopes are usually used on tactical scopes and similar, where parallax is adjusted before each shot and distances to the targets change rapidly. Scopes, which offer parallax adjustment with a side focus, are usually bigger and heavier than counterparts with parallax adjustment on Adjustable Objective. They are also more expensive to produce. Due to the size of the internal mechanism for side focus adjustment, the majority of such scopes have a tube diameter of 30mm or more.

The easiest way to correctly set the parallax is to look at the target and gently rotate the ring on the side focus. When the target is in focus and the image offers the best sharpness, move the eye from the optical axis to any direction. If the rifle is properly supported and fixed, the reticle should not move on the target when the eye is moved from the optical axis. If it does, parallax adjustment must be fine-tuned until the reticle is still, even if the eye of the shooter is moving around the optical axis.

Do not mind the meters or yards written on the adjustable objective, since they only provide an approximate value. There is nothing unusual if these values do not correspond well with the actual target distances.

Video presentation of Parallax adjustment on the objective bell

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VIDEO

As the name suggests, prism scopes (sometimes also referred to as prismatic scopes) are composed of glass prisms – like binoculars. As a result, they are a much more compact optic. These compact, robust devices work similarly as red dot sights but are usually equipped with an illuminated reticle in the shape of a dot or a cross, surrounded by a circle. BDC reticles for .223 are common in prismatic scopes.

The magnification for these products is lower, and fixed: 1x, 2.5x, 3x, 4x, or 6x. Nearly every prism scope has a Picatinny mount built-in on the bottom part of the housing.

Prism scopes give the user an option of choosing between green and red illumination. All in all, these scopes are a great choice as they give the user a brighter and extremely sharp image, providing quicker target acquisition times.

General properties of Prism scopes

a compact, robust scope
prisms in the interior of the scope
illuminated reticle
fixed magnification (1x, 2.5x, 3x, 4x or 6x)
scope with diopter adjustment

Prism Scopes

Steiner and Burris Prism scopes

Why are prism scopes better for astigmatism?

Prism scopes are a great substitution for red dot sights for people with astigmatism because they have a dioptre that can be adjusted for personal differences in vision. If a user with astigmatism uses a red dot, they cannot see a clear image of the reticle, the dot may glow or appear dispersed into a different shape.

This is where prism scopes come to the rescue, as you can adjust the dioptre setting so that your eye can see a crisp reticle because there is no distortion.

Also, people who wear glasses do not have to deal with the obtrusive reflection of the dot. This is a great fix, the only downsides are a smaller eye-box and the lack of unlimited eye relief.

Prism Scope

Steiner S332 3x Prism Scope

What is the difference between prism scopes and red dots?

The most significant difference between Prism scope and the Red dot is that red dot sights feature 1x magnification, while prism scopes can have various magnification powers: 1x, 2x, 3x, 4x, or 6x.
Prism scopes are lightweight and small, yet still bigger than red dots. They have reticles in a shape of a dot or a cross, surrounded by a circle, which is different from reticles in red dots, which have, as the name suggests, only a dot in the center.
The latter are unusable without battery-powered illumination, while prism scopes (with an etched reticle) work without batteries.
Prism scopes also oftentimes allow the user to switch between a red or green illumination, while red dots usually do not offer the same option (it is mostly only red).

Overall, red dot sights are used for close distances, while prism scopes for close to medium distances. But if you ever find yourself using a prism scope with 1x magnification, keep in mind that it can also be used as an alternative to a red dot.

Burris prism scope

Burris RT-3X Prismatic

Parallax adjustment with a side focus

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Video presentation of Parallax adjustment on the objective bell

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General properties of Prism scopes

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What is the difference between prism scopes and red dots?

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Parallax adjustment with a side focus

VIDEO

Video presentation of Parallax adjustment on the objective bell

VIDEO

General properties of Prism scopes

Why are prism scopes better for astigmatism?

What is the difference between prism scopes and red dots?

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