What is parallax and how can it affect your rifle shooting?

Parallax is caused by light bending as it passes from one medium to another. It’s why a fish or a stone under water will appear closer to you than it really is.

  • The light transmitted through a telescopic sight will bend as it passes through the various lenses unless (a) they are perfectly ground and (b) your eye is dead centre in the optic lens.
  • To check if your ‘scope has parallax, fix the rifle in some sort of clamp. If the crosshairs move on the target when you move your head up and down or side to side, then you have parallax at the range of that particular target.
  • Most ‘scopes are adjusted to be parallax free at about 100 yards (or metres) but some have parallax adjustment at the object glass (the end furthest from the eye). The figures on the ring may, or may not, be accurate and you won’t know without doing the above test at various known distances.

Does parallax matter?

If you always make sure your eye is dead centre (you have a perfectly symmetrical dark ring around the crosshairs) then parallax doesn’t matter.

Do I need a scope with parallax?

Q: I am in the market for a new scope for deer stalking and my gun shop says that I should get a scope with parallax adjustment as it is more accurate. Is that true?

A: Parallax in a scope is quite complex but makes a big difference to the performance of 
a scope and your shooting.

Parallax error is where the reticle seems to shift its point of aim on a target as you move your eye left or right while looking through the riflescope. This is why shooting technique and scope-to-eye alignment must be exactly the same for each shot. Most scopes designed 
for full-bore rifles are parallax free at 100 yards thus even some eye movement results in minimal parallax error. Rimfire scopes used at shorter ranges have a parallax set for 50 yards.

To allow for more flexibility some scopes, especially higher magnification and variable scopes, have an adjustable parallax ring either on the objective bell or side-mounted on the adjustment bowl. This can be used to eliminate parallax at any range while maintaining focus at closer ranges, even on the highest magnification. So yes, a parallax ring is useful, but if you hunt at short ranges with a lower-powered scope and position your eye the same for each shot, you will be fine.

More on parallax and scopes

Scopes are either set for one parallax-free setting or come with parallax adjustment.

Look through a scope from a differing angle each time and the chances are your shots will shoot differently.