The parallax of a riflescope is the accuracy error caused if the sight is not perfectly centred in the riflescope. If the eye is not exactly aligned on the optical axis of the rifle scope, there may be a difference between the crosshairs of the reticle and the desired point of impact.
Scope packing
Normally, a riflescope is set to 100 metres. Scope manufacturers follow this standard and ensure that the image obtained is located in the focal plane of the reticle at this distance. In other words, regardless of the alignment of the eye with the optical axis of the rifle scope, the target image remains in the focal plane of the reticle. Therefore, the riflescopes can be said to be parallax-free at 100 metres.
For distances other than the parallax-free distance, the image obtained is reproduced a few hundredths of a millimetre in front of or behind the reticle. As long as the hunter looks exactly through the centre of the rifle scope, the correct point of impact is maintained. However, if the hunter turns his eye slightly away from the optical axis, the point of impact shifts slightly with respect to the reticle.
Parrying at long distances
At long distances it is much more important to compensate for errors caused by bullet drop. At very short distances it can appear clear but with a blurred reticle because image and reticle are not in the same focal plane. This type of fine focus adjustment is generally reserved for high magnification riflescopes. It basically consists of an adjustment ring on the front lens (objective) or a side wheel that can be turned to find the best focus for that distance.
Elements influencing parallax
Not to forget that there are other elements that influence the point of impact, such as: the dispersion of the ammunition and the rifle, the side wind, the shooter, the incorrect estimation of the distance and the parallax due to the lack of alignment of the hunter.
Four different types of mounts can be used for this purpose: pivot mounts, lever mounts, the maker's mount and leg mounts.
Although quality is not easily detectable by the inexperienced hunter, economising on the quality of mounts is not a real saving. The lack of accuracy of hunting guns is often due to poor quality of frame construction.
