During the past few days, I participated in a parallax discussion on another thread in this forum. That discussion stimulated a bit of internet research which uncovered some very interesting results.
I've competed in various shooting disciplines over the years with a wide variety of riflescopes ranging from a 6 power Unertl Small Game scope up to Nightforce 15-55 Competition scopes. All this time, I've assumed that parallax error was a function of scope magnification. This seemed reasonable because the 6-8 power scopes had virtually no parallax error while the much higher power scopes required parallax adjustment for every change in distance.
It turns out that I was wrong. Maximum Parallax error is not a function of scope magnification. Rather it is a function of objective lens diameter. And, there is a formula to calculate maximum parallax error given the diameter or the objective lens, the distance at which parallax is zeroed, and the actual distance from muzzle to target.
Background
I wanted an inexpensive bullet-drop reticle scope for NRL-22. I'm old and slow so I chose a fixed 10 power SFP scope with a 40 mm objective. The low power provides for a wide depth of focus so I could set the focus at 70 yards and not have to take the time to refocus with each change in distance from 40 yards to 100 yards. This part works as predicted. I also assumed, incorrectly in retrospect, that the low power would also yield low parallax error from 40 yards to 100 yards. This assumption was incorrect. Zeroing parallax at 70 yards give me a 40 yard maximum parallax error of .806 MOA and a 100 yard maximum parallax error of .302 MOA. These are not insubstantial errors. Fortunately, I'm good at keeping my eye centered in the ocular.
The Maximum Parallax Error Formula
The parallax error formula, along with an excellent parallax error calculator can be found at https://www.lelandwest.com/parallax...onid=720BD8E8B3FC55A7B6D40669D1B3DFC0.cfusion
JackHughs
Note: I've edited this post to show that we are discussing "Maximum" parallax error. Based on the paper referenced in the following post, realizable parallax error can and will be less than maximum parallax error based on some additional variables. If I can, I 'll reduce the mathematics of realizable parallax error to plain English and post again.
JackHughs
I've competed in various shooting disciplines over the years with a wide variety of riflescopes ranging from a 6 power Unertl Small Game scope up to Nightforce 15-55 Competition scopes. All this time, I've assumed that parallax error was a function of scope magnification. This seemed reasonable because the 6-8 power scopes had virtually no parallax error while the much higher power scopes required parallax adjustment for every change in distance.
It turns out that I was wrong. Maximum Parallax error is not a function of scope magnification. Rather it is a function of objective lens diameter. And, there is a formula to calculate maximum parallax error given the diameter or the objective lens, the distance at which parallax is zeroed, and the actual distance from muzzle to target.
Background
I wanted an inexpensive bullet-drop reticle scope for NRL-22. I'm old and slow so I chose a fixed 10 power SFP scope with a 40 mm objective. The low power provides for a wide depth of focus so I could set the focus at 70 yards and not have to take the time to refocus with each change in distance from 40 yards to 100 yards. This part works as predicted. I also assumed, incorrectly in retrospect, that the low power would also yield low parallax error from 40 yards to 100 yards. This assumption was incorrect. Zeroing parallax at 70 yards give me a 40 yard maximum parallax error of .806 MOA and a 100 yard maximum parallax error of .302 MOA. These are not insubstantial errors. Fortunately, I'm good at keeping my eye centered in the ocular.
The Maximum Parallax Error Formula
The parallax error formula, along with an excellent parallax error calculator can be found at https://www.lelandwest.com/parallax...onid=720BD8E8B3FC55A7B6D40669D1B3DFC0.cfusion
JackHughs
Note: I've edited this post to show that we are discussing "Maximum" parallax error. Based on the paper referenced in the following post, realizable parallax error can and will be less than maximum parallax error based on some additional variables. If I can, I 'll reduce the mathematics of realizable parallax error to plain English and post again.
JackHughs
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