Advanced Marksmanship Rapid parallax adjustment

[m1ajunkie]

I am looking to start shooting more matches through this spring, and one thing I haven't figured out yet is how to adjust parallax on the fly.

I understand parallax and how to adjust for it when you have plenty of time, but what about when time is very limited. For example, say you are shooting a match with 300yd-800yd target distances, and you are not allowed to look through your scope prior to making a shot. In the limited time you get to make the shot, how can you quickly adjust parallax?

Or, what about when shooting targets at multiple distances within the 300-800yd window in the same timed relay?

Can you simply set parallax at some distance in the middle such as 500yds, or simply bring the image into focus and run with it?

Thanks for any tips.

 

[Killswitch Engage]

Re: Rapid parallax adjustment

not sure if this is "the" way but in your given example i would run the parallax at mid range and try my best to make sure i have absolute edge to edge clarity. thats what i do when i am under time or any other constraints.

ymmv

 

[The Mechanic]

Re: Rapid parallax adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: m1ajunkie</div><div class="ubbcode-body">Or, what about when shooting targets at multiple distances within the 300-800yd window in the same timed relay?

Can you simply set parallax at some distance in the middle such as 500yds, or simply bring the image into focus and run with it?
</div></div>
Yes for both. I like to close my eye for a minute or so and as soon as I open it adjust for focus and parallax, close eyes again and then fine adjust. Then just run with it. A little "tune" when you drastically change yardages may be needed but most of the time I set it and forget it.

 

[JFComfort]

Re: Rapid parallax adjustment

+1, I generally will go to a mid distance for the shots taken during the match. I usually wont touch the parallax again until we move to a 100 yard stage or a stage that will be shot at a single distance.

 

[Greg Langelius *]

Re: Rapid parallax adjustment

Parallax distorts the relationship between the reticle and the desired POA, making the eye's alignment relative to the scope's optical axis a matter of importance. This distortion is present to the degree by which the eye is off center with the scope's optical axis.

Technically, as long as the eye and optical axis are always in perfect alignment from shot to shot, then parallax can have no bearing on the relationship between reticle and POA.

So how can we ignore parallax with impunity and still get a good POA/POI relationship? It's about that eye/axis alignment.

We skip the nod/wag maneuver we normally use to see if parallax is present; and concentrate, instead, on getting the eye into perfect alignment with the scope's optical axis.

If you move the eye toward the edge of the eyepiece lens, you will reach a point where the image becomes 'shadowed' near the edge of the field of view. Going in the opposite direction, one encounters the same shadowing near the opposite edge of the field of view.

Logically, moving the eye to a position halfway between the shadow should place it at or very close to the optical axis. When we do this in both the horizontal and vertical planes behind the eyepiece, we've done a pretty good job of aligning the eye with the optical axis.

This process of centering the eye between the shadowing limits is sometimes referred to as 'quartering' the scope or the image. In order to deliver a consistent POI when parallax is present, it must be done with diligence, all over again, for each and every shot. A consistent cheekweld can be established that accomplishes this alignment, but it's a precise and iffy matter to depend solely on the cheekweld for this critical relationship.

While this can provide the solution to parallax that you seek, it's really not faster than simply fixing the parallax by the wag/nod/adjust parallax technique.

I suppose that for a single shot, on the fly, it can get you pretty close to an ideal solution, but fixing the parallax properly is really the better approach.

Greg

 

[Greg Langelius *]

Re: Rapid parallax adjustment

Getting the eye to the center by quartering takes time and can be difficult to do perfectly.

Suppose one were to 'mask' the eyepiece with a disk that obscures the eyepiece lens except for a peephole at its very center. In this way, the eye is forced to find the optical axis. The idea here that by forcing an optical axis/eye alignment, parallax error can be minimized, or maybe even eliminated. Maybe the shooter can stop having to settle for a less than perfect focus in order to achieve proper parallax correction.

The size of this peephole should be about the same as the scope's optical 'exit pupil' diameter.

We find this exit pupil diameter by dividing the objective diameter by the scope's magnification power, but technically, anything larger than the eye's actual pupil diameter is unusable by the eye.

So, a 50mm objective, divided by 24 power, delivers a an exit pupil diameter of just slightly greater than 2mm. For 12 power, it expands to just over 4mm. For a 40mm objective, at 20 power, it gives a 2mm exit pupil. Capice?

This is probably a radical idea, but I think it's easily proven. I'm going to try this 'objective masking' idea with one or more of my own scopes and see if it makes a difference in accuracy. It might even be as simple as drilling a centered 1/8" diameter hole an obective lens cap. Bigger than that is likely to be quite a bit larger than the eye's actual pupil diameter. Smaller might be better, but I'm pretty sure there's a limit with smaller. My guess is that 1/16" is too small.

If this idea works, I think it can become a valuable accuracy tool. It's my personal belief that as much as half, or maybe even more, of all inaccuracy is due to parallax error.

Meanwhile, if anybody's already tried this idea, or can see a valid reason to discard it, I'm open to suggestion.

Greg

 

[Christopher Rance]

Re: Rapid parallax adjustmen* (radical idea alert)

Interesting. I too think parallax is a key culprit in accuracy errors. I always try to adjust before I shoot or mil a target.

 

[GotM118LR]

Re: Rapid parallax adjustmen* (radical idea alert)

I put a piece of masking tape around my parallax knob, then set the parallax for different known distances and mark the distances on the tape. Kinda like a BDC knob but for parallax. Just turn to the correct mark or between marks depending on your actual range, then fine-tune if you have time. Of course this works better for closer-in distances from like 50 to 400, where you have to turn the parallax knob farther in between distances vs distances farther than that where the knob is closer to infinity. Been using this method for years and its alot faster than steeing parallax from scratch every time. Surprised I don't see more people doing it....

 

[AtOne]

Re: Rapid parallax adjustmen* (radical idea alert)

Greg that's a great thought and look forward to hear how it turns out.

I can see where something like that would aid in practicing a consistent cheek weld especially teamed up with the IOTA for dry fire practice.