Optics Master Extraordinaire
Another thread got me to thinking again about parallax adjustment and its necessity in a hunting scope. I recently changed a scope on a hunting setup from a tactical style side-parallax adjustable scope to a hunting-specific non-PA ballistic reticle hunting scope.
The lack of parallax adjustment was a feature I was looking for. I just seem to mess with the parallax adjustment too much in the field. I also thought that by keeping my eye centered behind the exit pupil, I could minimize the error.
Well I read a very interesting thread here:
The author walks throught he math, and comes to a simple equation for calculating Maximum Parallax Error (MPE). I began running some numbers through the equation and the results were interesting. The equation goes like this:
Maximum parallax error (in mm) at X yards =0.5(objective diameter in mm)(ABS(X-scope's parallax setting in yards)/scope's parallax setting in yards
In the other thread, posters were interested in the Minox 3-15X42 ZA3 riflescope, but were concerned about the lack of parallax adjustment. So lets say you want to know what the maximum parallax error of that scope would be at 600 yards. Minox's website lists the factory parallax setting for the scope at 100 yards. We will plug in the numbers:
MPE = 0.5(42)(600-100)/100
MPE = 105 mm or 4.13 inches or .65 MOA
And that is the MAXIMUM error. It is the amount of error introduced if your eye is in line with the very edge of the exit pupil. And that amount of error decreases substantially as you get closer to the center of the exit pupil.
I understand that it is good to eliminate as many variables as you can for shooting, but that is a small amount of error for the hunter, even at long ranges.
It is interesting to note that this equation does not account for magnification, but it would stand to reason that it would be easier for a shooter to line up his eye more towards the edge of a smaller exit pupil than a larger one, so it would be easier to introduce parallax error in a small exit pupil compared to a larger one.
I think hunters get a little too concerned about parallax. It is a different story with target/benchrest and tactical shooters.
What do you think?