Have a side focus or adjustable objective, then take two parallax and contact us in the morning.  Well that’s not quite right all be it a small attempt at some humor.

First up we’ll tackle parallax.  If your looking through a rifle scope, cross hairs are on the bulls-eye and you shift your head in just the slightest teeniest bit and the cross hairs appear to move around, that’s called parallax and we don’t want that.

Parallax can occur if the images is just a bit out of focus, even just a small bit that you cant even notice the image is out of focus.  So manufactures design scopes to be parallax free, but parallax free at a given range of distances and on lower magnification scopes such as a 3X to 9X or smaller while some manufactures allow you to change that given distance by making the front objective lens adjustable by removing the front trim ring, rotating the lens and replacing the trim ring to lock it in place. Nothing you would want to try out in the field on the fly.

So to avoid parallax at close ranges and high magnifications, rifle scopes are designed with a side focus or an adjustable objective.  On scopes designed for airguns, these focus adjustments can reach as low as 9 or 10 yards while on centerfire scopes the lowest setting is typically 35 or 50 yards.

Rifle scopes with a side focus or an adjustable objective will require the shooter to locate the target and then adjust the focus to bring it into a clear image.  On a  rifle scope with an adjustable objective, this focus adjustment is found on a ring around the large objective lens making it a little more difficult to adjust while maintaining good control of the rifle.  On a rifle scope with side focus, this adjustment has been moved to the user’s left hand side of the rifle scope opposite the windage turret making it much easier to access.  Although much more practical to have the focus on the side, it does add to the manufacturing cost as it requires the addition of a couple lenses inside the rifle scope.

Whether you have an adjustable objective or a side focus, both will be marked with distance readings. When the image is brought into clear focus, just a quick glance at the side focus or adjustable objective dial will give the user a reading on the distance to target and both are more accurate inside 100 yards or less.  Also, higher magnification scopes will be superior at giving more accurate distance readings than lower powered rifle scopes.