Parallax and Focus

R

Russ Hardy

Guest
Setting the eyepiece focus and eliminating parallax has recently come up on this forum. I would like to lay out my thoughts on this for review and consideration.

The thing that I am specifically trying to address is having the image of the target and the reticle both focused at the same time. This is the condition that puts the focal plane of both the image and the reticle on the same plane.

When I saw the post by Mike Marcelli and read his account of parallax being adjusted by the eyepiece it confirmed what I had experienced with March scopes. The image quality is so detailed with these scopes that your eye will focus on the target image due to it's fine detail. This contrasts with scopes lacking the image quality to draw your eye to the target image and instead your eye is drawn to focus on the reticle. This matters to me because I was initially experiencing some difficulty getting both clear target images and the ability to have the reticle stay clearly focused with no parallax.

As stated earlier the reticle and target must be focused exactly on the same plane in order to have a parallax free image. The only way I can achieve this myself is to do the following.

*****Method Deleted because it was flat out wrong!!!!!!!

The greater detail you can see in the taget image the more your eye will struggle to have both taget and reticle in focus. This really isn't a bad thing since it is essentially telling you that you have some parallax condition present.

Once I have completed this proceedure I am seeing a very clear and crisp image of both the target and reticle.

Now the question.

Am I doing this right??????????????????
 
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Standard practice

Point the scope at the sky and adjust the eyepiece until the reticle is sharply focused then tighten the lock ring against the eyepiece. Quick glances through the scope rather than staring through it will work best. When finished, you're done with that end of the scope so don't adjust it any further.

Now you are ready to bring the image and reticle planes together at a chosen distance. Point the scope on target and adjust the objective ring or the side focus knob until when moving your eye around the field of view there is no apparent movement of the reticle in relation to the target.
 
That is the exact proceedure I used previously. I wasn't getting the same results as I am now. I'm trying to figure out why? The proceedure you mention does not seem to provide me with the same level of image quality as my new proceedure does. I know that in theory the pointing at the sky proceedure should provide the same result. I'm thinking that my proceedure takes away the need to look away and then glance at the crosshair, maybe that is where I get inferior results. I actually sit and look closely at the target and watch for the reticle to fade. If it does I adjust the eyepiece untill I don't get any reticle fade while looking at the target.
 
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Russ,
It seems to me that the standard explanation and procedure for focusing the target and reticle images and achieving zero parallax are somewhat at variance with our experiences. Could it be that the commonly stated theory of how the whole system works is an oversimplification? Think about this. If zero parallax only can happen when the target and reticle are focused in the same plane, then how can you have a less than sharp target image and zero parallax? I too have found that I often get my sharpest target image with no parallax by working with small adjustments of the eyepiece. In the past, when I have posted this, on this, and other boards, I have had "experts" tell me that what I was reporting was impossible, sort of a” Who are you going to believe, me or your lyin' eyes?" situation. Well... short answer, my eyes.
 
OK, for those of you who're familiar with "the Dirty Steve Parallax Post" (like Boyd ;) ) y'all can just skip this post cuz it's looong!

I've been fighting with the focus/parallax thing too. I got one of those 3X optical multipliers that everyone's raving about........ Doesn't work A'tall for me......and now my 36 and 45 are all messed with and the booster is setting on the shelf. :( I've been using this method to put factory scopes back to whre they work for me. I'm not sure that it's relevant to your question Russ but I LIKE this guy so I figgered I'd post it up again.


-------------------------a post about parallax and focus -------------------------



Dirty Steve
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Proper Scope Adjustment
Ok, I am going to post this document. I would like to give a little info on how I got it. And the tone used by the author. I copied this and pasted it to MS Word off another site. And was sent a copy by the author after I contacted him directly. His tone may be a bit harsh, but this was written after responding o numerous questions about scope adjustment then having the person asking the question say well that's not how I was told to do it. Or another guy said to do it this way. The author is a man named Paul Coburn and his job is evaluating optics for a living. He is highly regarded in the field and does testing for some major companies. So no if's, and's or but's regardless of if you agree or disagree with the writting style he is giving the straight poop on the subject. Here it goes...


I've answered questions about scope parallax about 300 times, and it's always a long drawn out thing, going several e-mails, and a few phone calls. It doesn't seem to make any difference how long the guy has been shooting, this one always keep screwing guys up.
OK... here goes (Whew, this is gonna be a long one).
There are several things that go on inside a scope, and in the eyes at the same time. Some of them workie against each other.
But some terminology first... and we'll leave out lenses that are there to correct some optical or color errors, but don't have anything to do with image forming.
We'll start at the front of it all, and work back.
1 - The "Object"... the thing that you are looking (shooting) at.
2 - The "Objective". The front lens is called the "Objective"... it forms the first image of the "object" we are looking at (that why they call it the Objective
It is the lens that "captures" all the light, that is solely responsible for the image quality of the scope... if it is poor, you can't fix the poor image later.
This lens is usually made of two different types of glasses (called "elements") sandwiched together, and is called an "Achromat".
The Achromat is fully color corrected for blue and green. The red wavelengths are partially corrected, but have what is called "residual color errors".
This is the normal type of objective used in shooting and spotting scopes. In quality, they can vary from badd, through sorta OK, to pretty damn good.
If one of the elements is made of an "ED" glass, or a "Fluorite" (CaF) glass, the two element lens can be very good to friggin' outstanding.
In some instances, objective lenses are made of three elements, and all three colors (blue, green, and red) are completely corrected. This type of lens is called an "Apochromat", and this is the finest lens that can be bought. The best of these can also have "ED" glass, or Fluorite as one of the elements.
3 - The "First image plane". The Objective focuses the light to make an image of the subject, just like a camera lens. This image is upside down, and right/left reversed. This is the first image plane, but NOT the "First image plane" that is talked about when shooters talk about reticles.
4 - The "Erector lens"... (if it is a group of lenses, it is called the "Erector cell"). Because the first image is upside down/wrong way around, we (as shooters) can't use it... so we flip it around with a simple optical group called the "erector cell". This cell gives us a new image that is right way around, called the second image plane. Moving this cell causes this second image plane to move... so micrometer spindles are put against the cell, to get elevation and windage adjustments.
5 - The "Second image plane". This is the second real image plane in the scope, and this is the image plane that shooters call the "First image plane" when talking about reticles. In a fixed power scope, or in a variable with a "First image plane reticle", the reticle would be placed in this image plane.
This is where Premier Reticle puts those magical "Gen II" reticles.
6 - The "Zoom group". In a variable scope with standard (non-magnifying) reticle, the zoom group of optics would follow #5. This group of lenses can change the size of the image plane in #5 and then form a new (third) image plane behind it.
7 - The "Third image plane" In variable power scopes, this is the plane that the reticle is placed in. By being here, it allows the image to change sizes, but the reticle to stay the same size. In the context of reticles, this is the image plane that is referred to as the "second image plane"
8 - The "Eyepiece". This optical group is like a jewelers loupe. Is is (or should be) a super fine magnifier. It's only job in the whole world, is to focus on the reticle.
Let me repeat that for those that live in Rio Linda...
THE ONLY JOB FOR THE EYEPIECE IS TO FOCUS YOUR EYE ON THE RETICLE!!!!
It CANNOT adjust, or compensate for, or do anything else when things look bad in the scope, or when you can't hit the target... and you CANNOT use the eyepiece to try to correct for parallax. That is sheer folly at best, and raw stupidity at worst.
If you expect it to do anything else, then stop wasting your time with long-range shooting, cuz you are never gonna make it past mediocre... and take up golf!!
OK... now that you know what the insides are like... lets move on. We'll use the zoom scope for our examples. cuz if you can understand the zoom scope, then the fixed scope is a walk in the park.
In the scope that is set for infinity range, the object forms an image behind the objective (the first image plane)... the erector cell "sees" that image, and flips it over and makes it right way around in a NEW image plane (the Second image plane). The zoom group adjusts the size of this image plane, and makes a NEW image plane (the Third image plane) that is the desired size. There is a reticle placed in this last image plane, and the eyepiece focuses on the reticle AND the image at the same time.
When things are good, that's how the scope workie!
---
But... now the booger falls into the soup... IF the third image plane and the reticle are not exactly, (and I mean EX-ACT-LY) in the same place, then your eye cannot see them LOCKED together as one picture.
It sees them as two separate pictures, and the eye will look at each separately, and the eye can also look AROUND one to see the other.
---
Lenses are measured in metrics (aka Millimeters). Not because the Europeans wanted the metric system 20 years ago, but because optical strings and chains of lenses (like scopes) are really a string of numbers.
There are constant ratios of "this divided by that's" that give image sizes, "F-ratios", and image locations. It's so damn easy to do the engineering using a 10 based system that the optical guys were using the metric system way back in the 1800's.
The objective has a "Focal length"... this is the distance behind the lens that the first image plane falls when making an image if a subject that is at infinity (or very damn far away).
If the objective has a focal length of 100mm, then the image of that 1000 yd target is 100mm behind the lense.
But the problem with geometric optics (which is what we are dealing with here), is that they follow the laws of geometry... and optics make triangles like rabbits make babies.
AND... in an optical chain, when you change one thing, one angle, one ANYTHING, everything else follows along and changes BASED on the ratios involved at THAT stage.
If we take that same target, and move it to 100 yds, the image in the scope moves BACKWARDS, going further into the scope. Not by much, but it doesn't take much, cuz we're dealing with very small distances inside the scope, and very high magnifications.
How far the image moves back, and what it's new position is, is predictable by the mathematical ratios of the angles formed by the subject and the first image... OR (for us dummies that lost our slip sticks) by the ratio of the distances to the Target and the focal length, multiplied by the focal length. then ADDED to the focal length.
The target is at 100 yds (91440mm), the focal length of the objective is 100, so the displacement is 1/914 x 100, which means that the first image is now at ~100.1mm. Hmmm only .1mm, that doesn't seem like much.
Read the following paragraph twice...
In a 1x scope, 0.1mm would mean nothing... but this displacement is repeated throughout the chain, AND if any of the optical groups change the image ratio (aka image size), then the displacement (aka ERROR) is changed in direct proportion to the increase in magnification. So in a 3x scope, it would be .3mm, and in a 10x scope, it would be 1mm, and in a 30 power scope, the image would be 3mm behind the reticle.
Now, you should have seen a pattern in this last paragraph.
READ THIS TWICE!!
With the same error in the objective (scope focused at 1000, and target at 100), the parallax INCREASES WITH MAGNIFICATION... got it?
If not, READ IT TWO MORE TIMES!!
OK... now, if we do the same math for closer distances, like 50 yds, and 25 yds we will see that the error gets really big, so that with a target at 50 yards, and the scope set at 35 or 65 yds, the parallax makes the combination un-usable.
---
Parallax is... when the image of the target, and the reticle, are NOT in exactly the same plane, and by moving the eye up and down... or side to side, either the target OR the reticle appears to move in relation to the other.
You might see the target move and the reticle stay still, or you might see the target stay still and the reticle move over it... both are exactly the same, and which you see, is only a matter of your OWN perception.
It is NOT possible to have parallax while moving up and down, but not have it when you are moving side to side.
If you think that is what you have, you have other problems... either you are moving the rifle, or you have eye problems.
---
HOW TO SET UP A SCOPE!
This is the only way to do it...
First, screw the eyepiece out (CCW) all the way, until it stops.
If you wear glasses, put them on.
Hold the scope up and look OVER the scope at the sky, and relax your eyes. Then move the scope in front of your eye.
The reticle should look fuzzy
Turn the eyepiece in 1/2 turn, and do the same thing again. You will have to do for a while before the reticle starts to look better. When you start getting close, then turn the eyepiece 1/4 turn each time.
Do this until the reticle is fully sharp and fully BLACK immediately when you look through the scope.
Than back off one turn and do it again to make sure you are in the same place.
Then LOCK the ring on the eyepiece, and leave it alone forever!
Second.
Set the scope down on something sold, where it can see something at a long distance... half a mile of longer is good.
It can be on the rifle, and rested in sand bags at the range... but pick something at least 1000 yds away... even further if possible.
If the scope has an "AO" Adjustable objective, then set it for infinity, and look at the distant object, and move your head from one side to the other, or up and down if you prefer.
If the reticle seems to move, there is parallax.
Change the distance setting and try again... if you are very careful, you can move your eye, and adjust the distance at the same time, seeing which direction gets better.
With front objective adjustments, you can turn them either way without worry... BUT with side adjustment scopes, like the MK4-M3, the M3-LR, or the other LR family of scopes, the adjustment must ALWAYS be made from the infinity end of the dial. Turn the adjustment all the way until it stops (past infinity), and then start turning it in a little at a time, until there is no parallax. If you "overshoot" the proper setting, you can't just turn back a little, you must go back to stop at the end of the dial, and start over again.
While "AO"s dials are locked in place, and if the indicated distance doesn't match the real distance, there's nothing you can do about it... the side focus dials are not locked in place.
Once you have found the setting for infinity on the side focus models, then (CAREFULLY) loosen the screws, and set the dial so that little sideways infinity symbol is lined up with the hash mark, so it is calibrated. You can also make little marks or put on a paper tape for other ranges instead of using the round dots that don't match any range.
Now you can set it to infinity, but remember that you MUST turn the dial all the way past infinity to the stop, EVERY TIME before going from a close range to a longer range.
If you are set for 500 yds, you can go directly to 100 yds, but if you are set for 100 and want to set it to 500, you MUST go all the way back to the stop, and then go to 500
This is because there is a fair amount of backlash (aka SLOP) in this wheel linkage to the focusing cell, so you can set it only from one direction to make sure the slop is always on one side. The other problem with it is, even if you decided that you wanted to calibrate from the other end... the recoil will push the cell back. SO you must ALWAYS set these dials from the infinity end of their scales.
To make it easy to not have to remember... I always start from the end stop, when I change range, no matter which direction I'm going in... it adds about 0.023 seconds!
---
Now... you gots a friend that says to set up a scope a different way???... he don't know doodly-squat about scopes.
The guy at the range said to do it a different way... he don't know either.
You know some guy who's in the Marines says to use your eyepiece to correct parallax... he doesn't know about optics either.
You got a friend that shoots benchrest and says something different... he don't know crapola!
This is the way, the only way, there is no other way.
... as Rushbo would say... this is from GOD-da .
You gots questions, just e-mail me.
You wanna "debate it", then go play golf, cuz you're wasting my time!
'lito (gettin' grumpy in my old age!)

I hope this was helpful and did not burn up to much bandwidth. Again Paul deserves all the credit for the information not me...
Dirty Steve, Out.
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What I wrote is how it is. "How it is" can get fuzzed up a bit if you let some small details slip by - but its still how it is.

Now if you read Al's long post you may have noticed some attention to details such as slop or backlash in the system and the actual technique used to set the eyepiece for reticle focus, objective focus and co-incidence of the two.

The mechanical problems become obvious once given a bit of thought. The original poster's words spent on how to overcome the mechanical problems make sense but may not be the answer for every scope out there. Each machine is different. If you get something that works then keep doing it but you might find something coming back to bite you. Or might not. Your good result might be accidental.

As for the technique used to establish reticle focus you do have to take into account the likely error of a fairly coarse adjustment and the fact that your eye will attempt to adjust or focus on whats in front of it. Thats why using quick glances is preferred instead of staring at the crosshair. "Bracketing" your adjustment of the eyepiece may be a good way to hit right in the middle of the range of good focus.

I think the reason you're getting poor results from the standard method is that you're not following the instructions. You simply may not be accomplishing the reticle focus that you intend.

I'd go back to setting the reticle focus after re-reading Al's post about that process. Think about the possible reasons for doing it the way the guy tells you.
 
After reading Alinwa and Boyd's posts and thinking about it, I think I have it figured out.

First, Alinwa and henrya's posts are absolutely correct!

Second I'm seeing exactly what Boyd describes.

Now there is usually the same reason why a perfectly stated proceedure will not always give perfect results. Assumptions!

The procedure stated in Alinwa's post is clear that once the eyepiece is focused on the reticle it should be locked and left alone. I think where some of us have problems is gettting this setting PERFECT using the look at the sky procedure. Many of us probably make the assumption that the eyepiece is focused correctly on the reticle and move on from there.

The only way you can have the condition of a perfectly clear target image along with a perfectly clear reticle is when they are focused in the same plane. This will by defenition give the condition of zero parallax. The rub comes when I try and use the adjustments on the scope to make this happen.

Now there are only 2 things I can adjust on my scopes. The eyepiece focus on the reticle and the target image focus.

The eyepiece focus on the reticle is pretty straight forward. I'm simply moving the focal plane of the eyepiece to match the plane in which the reticle sits. End of story.

The target image focus (or "parallax adjustment") simply moves the focal plane of the target image. This is where it gets interesting to me. If the eyepiece is perfectly focused on the reticle then when the target image is focused you will get zero parallax. All 3 things are in the same plane. Life is good. Now what if the eyepiece focus is not set perfectly on the reticle plane? Well we now have the reticle on one plane and the eyepiece focus on another plane. Now as we adjust the target image focus (or "parallax adjustment) we can only have either the target image perfetly clear, OR!!!! we can have zero parallax. If the eyepiece isn't perfectly focused on the reticle you cannot have both zero parallax and the best target image. I find it interesting that you can have one without the other when the eyepice isn't properly focused.

Now how do I get the eyepiece focused perfectly on the reticle? You can try the look at the sky method. I have trouble with that sometimes.
The method I'm going to try is the following,

1. Pick a time of day with as little mirrage as possible and set my bench gun up on a solid bench with a solid rest set up. This is essential to see parallax in my scope by moving my head behind the eyepiece.

2. Move the target image focus ( "parallax" adjustment) until i get zero parallax. I now have the target image on the same plane as the reticle. Parallax is completely independent of the eyepiece focus!!!!!!!!!!!!

3. Adjust the eyepiece focus until the target image and reticle are very clear in the scope. I'm just moving the focal plane of the eyepiece to match the focal plane of the target and reticle which I have already established together.

4. Repeat steps 2 and 3 to make sure I have it right.

The advantage of this method for me is that I can use the superior image quality I'm getting with my new scopes to really fine tune these focus settings. Now I can look at the target and take my time evaluating the image instead of just peeking at it while looking at the sky.


Boyd, I believe that what both of us are experiencing is the eyepiece not PERFECTLY focused on the reticle. With this condition we can only achieve either a perfectly clear image and some parallax or no parallax and a somewhat diminished image quality. When the eyepice is adjusted properly we are simply getting both zero parallax and ideal image quality.

hernya, your right. I was typing this while you made your post. I'm just trying to come up with a procedure that works a little better for me.
 
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Russ,
I believe that what you wrote describes the situation. Essentially, there is so much depth of field in the focusing of the eyepiece on the reticle (doesn't snap in and out of focus as dramatically as the target with the adjustment of the objective) that it is easy to be a little off and still see a sharp dark reticle against the sky, even with only a quick glance. By setting the objective at peak target sharpness, and going back to make a small correction at the eyepiece one is using the parallax, or rather the point of eyepiece focus where it disappears, to get the eyepiece in perfect adjustment. The fact that the more inflexible among us cannot "see" how this procedure would work does not worry me. I am not selling anything, just reporting, and in doing so, not trying to defend my expertise. I claim none. BTW, my vision corrects to 20/15 or slightly better on a good day.
 
And then there is the cheap, simple way to eliminate the effects of parallax even with a cheap bargain scope without AO. :D

Get the scope close to zero at or around the range you expect to be shooting (say 50 yards or so).

Get a clear see thru lens cover for the occular lens (eyepiece) - The "Blizzard" covers work well.

Put a piece of thin tissue between the eyepiece and the cover.

Point the scope at a fairly bright light source and mark where the exit pupil is.

Remove tissue paper (it was just there as a "movie screen" anyways).

At the center of this circle draw a smaller circle (say around 1/16" to 1/8" depending upon your preference).

Hold the shadow of this circle centered around the crosshairs.

How does this eliminate parallax? It doesn't - it eliminates the EFFECTS of parallax by giving you a reference to go by that insures that your eye is in the same place each time. The gross parallax between this circle and the image focal plane is easy to see and detect, unlike the difference between the image plane and the reticle.
 
Russ wrote:
"3. Adjust the eyepiece focus until the target image and reticle are very clear in the scope."

Russ - What you are doing here is covering your previous mistake. And you may end up with all three planes more or less focused. If it works for you fine. But if you don't want to mess with both adjustments every time you change yardage then focus the reticle correctly the first time and be done with it. Even if that means spending an hour fooling with it you're better off in the long run.

Boyd - in your reply the depth of field that you refer to results in an illusion of sharpness or could be thought of as a range of acceptable sharpness. (technically depth of field is around the object being viewed, depth of focus is what you are referring to back in the optical system) There is only one precise plane of perfect focus. Move off of it in either direction and you will lose sharpness. The range around the perfect plane of focus is depth of focus. You'll have what looks like acceptable focus until the error reaches the human eye's ability to resolve. Once the error becomes visible you become aware that its there. Until you can see it - well, you can't. That your eyes correct to 20/15 has nothing to do with this. (good for you though)

Boyd wrote:
"The fact that the more inflexible among us cannot "see" how this procedure would work does not worry me."

Its physics Boyd, not any need for me to to be an expert. If you prefer to depend on "guess and by golly" have at it.
 
henrya,
You are correct. I am trying to fix my previous inability to focus the eyepiece correctly on the reticle. That is the whole point. I'm trying to find a way to get it right. Why should I need to mess with the eyepiece when I change yardages? Once I have the eyepiece focused perfectly on the reticle, by whatever means I'm able to accomplish it best, it should stay focused.

I've taken a few physics tests myself, but it has been a while. I'm really just trying to figure this out and not trying to be argumentative. I thought my procedure above adhered to the laws of physics.

I'm going to give it a try anyway and see if I get better results than I was getting before.
 
Vibe,
Hey why not save a tree and not waste tissue paper. Just move your head back from the scope until you only see a little circle of image. Center that image in the scope and remove the effects of parallax with less investment.:D
 
If my eye cannot tell the exact point of perfect reticle focus by the oft cited "glance at the sky" method, how is using the final disappearance of parallax as a way to tell when that point is reached contradictory of physics? The method that I described has, in fact, proven to be a practical method that has worked on more than one occasion. Once my eyepiece focus is correct, by this method, at 100 yd., it has proven to be correct at 200yd. Having verified this in the early morning, when there is no mirage, it gives me the advantage of knowing that if I focus my objective for peak target sharpness when there is too much mirage running to make a determination, by observation, of zero parallax. Adjustment until the desired result is achieved would seem to me to be the exact opposite of guessing. When "it works" ceases to be an adequate argument, it would seem to me that we are in area where conformity to a long standing explanation is more the issue, rather than actual performance.. An unrelated example would be the seven years that it took the medical establishment to accept that many ulcers are caused by a bacterial infection. They were all experts, and just knew that it couldn't be right. I will always listen, but in the final analysis, I believe my eyes, particularly when it comes to optics.
 
Russ Hardy said:
Vibe,
Hey why not save a tree and not waste tissue paper. Just move your head back from the scope until you only see a little circle of image. Center that image in the scope and remove the effects of parallax with less investment.:D
Click to expand...
LOL. I can afford that investment. :D
And I've never been able to shoot well with my head that far back. :D
 
Russ

Russ Hardy said:
Once I have completed this proceedure I am seeing a very clear and crisp image of both the target and reticle.

Now the question.

Am I doing this right??????????????????
Click to expand...

parallax is present when the target image is not focused precisely on the reticle plane. That's why its important to focus the reticle with the eyepiece then dial out the parallax with whatever mechanism your scope provides. Strictly speaking if you look directly at the target through the exact center of the scope there can never be any parallax. It only shows itself when you are looking at the target slightly off center.
 
Gents,
I think I misunderstood that you would use the eyepiece and side knob every time you adjusted the scope for distance. I think I understand now that you meant that you'd do eyepiece focus once and subsequently use only the side knob.
 
Like jackie once said ...

somethings can get over complicated or something like that. Here is a procedure I adopted and it has served me well. This man knows what he's talking about. He's had lots of experience with scopes. Art

Retical and Parallax Adjustment ... by Wally Siebert

1. Adjust the "eyepiece" by unscrewing it until it is fuzzy.

2. Point the scope at the sky, a white wall or a fluorescent lamp.

3. Turn the eyepiece in "one" turn. Take a look. If fuzzy, do the same routine until the reticle is sharp and black.

4. Lock the eyepiece and leave it until your optometrist gives you a new prescription.

5. Direct your attention to the target and "adjust the parallax" setting until the target is sharp and clear!

6. This setting can vary from range to range depending on the elevation.
 
abintx said:
3. Turn the eyepiece in "one" turn. Take a look. If fuzzy, do the same routine until the reticle is sharp and black.
Click to expand...

I wish I could do it that way! On my Leupolds, the adjustment is so s-l-o-w that my eye fools my brain most of the time. However, I was given a solution, that is go from just fuzzy thru focussed to just fuzzy on the other side while counting the turns, then halve the distance for the best chance of a good focus.
 
Focus

Try this , Place a white handkerchief over the objective lens and point a bright light at it. Then turn the eyepiece to bring the recticle in focus. I've used this method for years, sitting at my workbench. It's a lot easier then trying to hold the rifle while aiming at the sky, and a lot quicker.
Jerry
 
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