Rifle Scopes Parallax keeps Changing

[jawa]

I was out shooting about a month ago, 55 degrees outside, 78% humidity, overcast. While I was shooting I was marking my position on my parallax knob when I was parallax free from ranges 100-600yds. I had no verticle or horizontal movement on the reticle at each distance. I was bug-holing all day long at 100-300yds, and putting up the best groups I ever had at 600yds.

So I go out this past friday, 81 degrees, 78% humidity, no overcast. But when I tried to use the markings I made for my parallax adjustments the last time I shot, I was not parallax free at each distance... So I had to find the parallax settings all over again.

I dont know what changed between those two shoots... My question is:

Does your parallax adjustment change depending on the conditions of the day, or is my diopter not set correctly? Or was it something else?

I would like to have my parallax settings marked for distances without them changing each time I go out and shoot.

 

[Bugaboo]

Re: Parallax keeps Changing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jawa</div><div class="ubbcode-body">I dont know what changed between those two shoots... </div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jawa</div><div class="ubbcode-body">55 degrees vs. 81 degrees</div></div>

The scope dilates with changing temperature and paralax setting is basically setting of distances between internal components of the scope.

In other words: at 55 degrees the distance between the reticle and objective is different then at 81 degrees. The paralax setting changes with temperature.

 

[HillbillyfromAL]

Re: Parallax keeps Changing

So if you keep your scope cold it won't have parallax? WTF Over

How was the mirage on the warmer day? Mayb that made your eye more sensitive to the focus. It could also have been your position. Parallax is usually different for me at all the different ranges, and I've never found temperature to be the reason why. Mirage on the other hand can make getting the parallax right difficult. What optic are you using?

If your diopter isn't set right your eye will switch focus inbetween the reticle and target and you won't be able to set your parallax right.

 

[Bugaboo]

Re: Parallax keeps Changing

The paralax will always be there. Just the setting changes with the temperature. Other atmospheric variables don't come into play - paralax setting changes internal configuration of the scope.

The scope dilates with increasing temperature, it is physics.

The paralax setting adjusts the distance between the reticle and the objective lenses. In other words the focal point of the objective for different ranges (at a given temperature) is in a slightly different position and you need to move the reticle into the focal point to see the target and reticle sharply.

If the length of the scope changes with temperature, the distance between the reticle plate and the objective changes as well (the focal point for particular range moves).

We are talking very slight dilation, but in terms of optical systems it is important. The changes in optical systems with temperature are not limited to rifle scopes. Astronomical telescopes have the same problem.

This link has a nice picture of a 1st FFP scope cross-section, just for illustration: http://www.meoptasportsoptics.com/cata.php?cata=7&nav1=2&nav2=3

 

[E. Bryant]

Re: Parallax keeps Changing

While the scope body does indeed change dimensions ever so slightly with temperature, there is a much more probable reason for the OP's issue - a bit of hysteresis (lash) in the parallax mechanism.

 

[Bugaboo]

Re: Parallax keeps Changing

Of course hysteresis is another possibility, depends on the quality of the scope. I discussed this with a shooting buddy who works for Meopta in a lab and I simply posted explanation I was given by him-expert.

It should be possible to determine the amount of hysteresis - turning the paralax dial in one direction to a certain setting and then from the other stop position to the same setting.

 

[jawa]

Re: Parallax keeps Changing

I am using a NF 5-22x50 mil/mil HS ZS with the MLR reticle. I have 20/20 vision, no astigmatisms, etc... I adjusted the diopter position where it is turned in completely, thats where it seemed crisp everytime I moved my head back and forth.

 

[Bugaboo]

Re: Parallax keeps Changing

One thing is setting the correction on the ocular and another is setting the parallax.

 

[DerMeister]

Re: Parallax keeps Changing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jawa</div><div class="ubbcode-body">I adjusted the diopter position where it is turned in completely, thats where it seemed crisp everytime I moved my head back and forth. </div></div>

Is the diopter sometimes called the ocular focus?

If so, that's not how you adjust the diopter, and having it turned all the way is probably not correct for your vision as we have the same vision.

You need to set your parallax to infinity.
Point your scope at a cloudless sky.
Screw your ocular focus all the way out.

Then only looking at your reticle for a few seconds each time, make small adjustments to your ocular focus. Keep making adjustments until the reticle is crisp. The process should take several minutes at the very least.

The idea is to not have your eye focusing to the reticle, but rather the reticle adjusted to your eye.

At least this is my understanding.

 

[Bugaboo]

Re: Parallax keeps Changing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DerMeister</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jawa</div><div class="ubbcode-body">I adjusted the diopter position where it is turned in completely, thats where it seemed crisp everytime I moved my head back and forth. </div></div>

Is the diopter sometimes called the ocular focus?

If so, that's not how you adjust the diopter, and having it turned all the way is probably not correct for your vision as we have the same vision.

You need to set your parallax to infinity.
Point your scope at a cloudless sky.
Screw your ocular focus all the way out.

Then only looking at your reticle for a few seconds each time, make small adjustments to your ocular focus. Keep making adjustments until the reticle is crisp. The process should take several minutes at the very least.

The idea is to not have your eye focusing to the reticle, but rather the reticle adjusted to your eye.

At least this is my understanding. </div></div>

Exactly!
And when you complete the above described process, you can adjust the parallax.

 

[HillbillyfromAL]

Re: Parallax keeps Changing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DerMeister</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jawa</div><div class="ubbcode-body">I adjusted the diopter position where it is turned in completely, thats where it seemed crisp everytime I moved my head back and forth. </div></div>

Is the diopter sometimes called the ocular focus?

If so, that's not how you adjust the diopter, and having it turned all the way is probably not correct for your vision as we have the same vision.

You need to set your parallax to infinity.
Point your scope at a cloudless sky.
Screw your ocular focus all the way out.

Then only looking at your reticle for a few seconds each time, make small adjustments to your ocular focus. Keep making adjustments until the reticle is crisp. The process should take several minutes at the very least.

The idea is to not have your eye focusing to the reticle, but rather the reticle adjusted to your eye.

At least this is my understanding.</div></div>

That is the correct way to set the diopter/ocular focus. However, everyones eyes are different it's not just based on having the same prescription. FFR

 

[DerMeister]

Re: Parallax keeps Changing

I am aware, he just said his vision was 20/20 with no astigmatism, same as me(in my right eye), and that his eyepiece was turned all of the way in. My scopes are adjusted near the mid-range of the adjustments, so I assumed his should be around there as well. Him saying his was turned all of the way in indicated to me it was probably not adjusted properly.

Our ocular focus should be adjusted similar for those with the same vision, yes? Not exact by any means, but close enough to where it's obvious when they're not properly adjusted?

 

[jawa]

Re: Parallax keeps Changing

Well, thats the way I did it. The eyepiece was about a 1/4 of the way out and the reticle was blurry for me. As I turned it back in it got crisp for me, and it just so happened that it was pretty much against the tension ring which was screw in all the way. I will look at it again but I'm pretty sure thats were its going to be best for me. Just like my USO's, the diopter ring on the eyepiece is screwed all the way in.

 

[DerMeister]

Re: Parallax keeps Changing

Yea there is still a lot I do not know, was hoping that was your issue.

 

[Hellbender]

Re: Parallax keeps Changing

You are mistaking parallax adjustment for focus, not the same thing at all.

Most people use the parallax knob for a focus knob.

My parallax yardage markers are correct on my S&B, but many times (esp. high temp conditions) the clearest focus may be 200-400 yards different than correct parallax adjustment.

 

[HillbillyfromAL]

Re: Parallax keeps Changing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DerMeister</div><div class="ubbcode-body">

Our ocular focus should be adjusted similar for those with the same vision, yes? Not exact by any means, but close enough to where it's obvious when they're not properly adjusted?</div></div>

No each persons eye is different. A guy with horrible vision may use the same setting as you. Most scopes adjust the diopter inbetween +/- 3. For example I now have 20/20 vision and for me I'm only about half a turn from all the way in on my Vortex Razor, and about 2 turns on my MK4.