One of the conditions encountered when using telescopes is parallax. To perform optical alignments properly, you should have a clear understanding of parallax and the procedures used to eliminate it.Parallax exists when the two lens systems of a telescope (the objective system and the ocular system) are not both focused on the reticle plane. You can check for parallax by moving your head up and down as you look through the scope. If you see relative motion between the reticle pattern and the target, you should correct the parallax by properly focusing the ocular and objective lens systems.
Here's how ...
(Note: Any time you sight through a telescope, keep both eyes open. This reduces eye fatigue. Initially, it may take some practice to concentrate on the proper image with both eyes open.)
- Point the telescope at a light colored object such as a wall, window, or piece of paper.
- Focus the eyepiece until the reticle pattern is sharp and clear.
- Aim at your target and focus the telescope using the focusing knob.
- Move your eye slightly left and right or up and down.
Note: Each user who looks through a telescope must re-adjust the eyepiece to account for differences in eyesight.