Causes of parallax
A normal riflescope generates an image of the target in the reticle plane – if the target is 100 m away! This is comparable to a camera lens that is set to a focal distance of 100 m. At a range of 300 m, the image is somewhat in front of the reticle plane. There are no problems except for a certain amount of blurring in the image at high magnification as long as the shooter is looking directly through the center of the eyepeice.
However, if the shooter looks through the eyepiece at an angle, the distance from the image plane to the reticle plane results in lateral offset between the reticle and the image and thus in a deviation in the point of impact.
Compensation
This is only relevant for practical everyday hunting with high magnification at long range – this cannot explain a miss with 10x magnification at 150 m. However, precautions should be taken to eliminate these potential mistakes.
Long range riflescopes from ZEISS including high magnification are equipped with parallax compensation, i.e. an easy to use swivel with a range scale from 50 m.
This moves the image back to the reticle plane, providing two huge advantages:
- the image is sharply focused and
- parallax errors cannot occur even when looking through the eyepiece at an angle.
The position of the reticles – in the 1st or 2nd image plane – is irrelevant.
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