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Parallax error- finally cracked the enigma!!!

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:03
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I have been searching the www for a while now in order to find a definitive work on parallax error and distance to the target.
It is official boys (and girls), the further or closer the target moves away from your parallax free distance (normally 100yds factory set), the greater parallax becomes.
The parallax error increases with objective size.
The parallax error measured in MOA is greater at 25 yds then at 300yds, but not when measured in inches.
 
EXAMPLE 1:
Assume we have a 3-9X32mm scope, where objective diameter, D = 32mm, parallax range of scope (p) = 100 yards, and the user desires to calculate maximum parallax error for target ranges (t) at 25, 50, 150,175, 200 and 300 yards. Using Equation 3, we get:

Maximum PE @ 25 yards = 0.5 * 32* ABS(25-100)/100 = 12mm or 0.47 inches,
Maximum PE @ 50 yards = 0.5 * 32* ABS(50-100)/100 = 8mm or 0.32 inches,
Maximum PE @ 150 yards = 0.5 * 32* ABS(150-100)/100 = 8mm or 0.32 inches,
Maximum PE @ 175 yards = 0.5 * 32* ABS(175-100)/100 = 12mm or 0.47 inches,
Maximum PE @ 200 yards = 0.5 * 32* ABS(200-100)/100 = 16mm or 0.63 inches,
Maximum PE @ 300 yards = 0.5 * 32* ABS(300-100)/100 = 32mm or 1.26 inches.

To convert this to an angular error, in MOA units, divide the maximum PE by t, where t MUST be in same units as linear Maximum PE, and multiply by 3438 to convert radians to MOA. The value t at 25yards = 22860mm, 50yards = 45720mm, 150yards = 137160mm, 175yards = 160020, 200yards = 182880mm, and 300yards = 274320mm.

Maximum PE @25 yards in MOA = 12mm *3438/ 22860mm = 1.80 MOA,
Maximum PE @50 yards in MOA = 8mm *3438/ 45720mm = 0.90 MOA,
Maximum PE @150 yards in MOA = 8mm *3438/ 137160mm = 0.20 MOA,
Maximum PE @175 yards in MOA = 12mm *3438/ 160020mm = 0.26 MOA,
Maximum PE @200 yards in MOA = 16mm *3438/ 182880mm = 0.30 MOA,
Maximum PE @300 yards in MOA = 32mm *3438/ 274320mm = 0.40 MOA.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:11
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8shots, did you test it with a few different scopes to see if it holds up? 
 
I've always read parallax error will increase with magnification, is it in the formula?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:12
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Ok for magnification it increases:
 
PE @ 25 yards with a 1mm offset from optical axis @ 3X = (1.0) (3) ABS(25-100)/100 = 2.25mm
PE @ 25 yards with a 1mm offset from optical axis @ 9X = (1.0) (9) ABS(25-100)/100 = 6.75 mm

To convert these PARALLAX ERRORS from linear to angular errors, in MOA units, divide by t, where t MUST be in same units as PE (100 yards = 91440mm in this case), and multiply by 3438 to convert radians to MOA.

PE in MOA @ 25 yards with a 1mm offset from optical axis @ 3X = (2.25)(3438)/ 91440 = 0.085 MOA
PE in MOA @ 25 yards with a 1mm offset from optical axis @ 9X = (6.75)(3438)/ 91440 = 0.254 MOA
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:13
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I was specifically interested at a set magnification and varying distances.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:27
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Thanks bud, I didn't know if it was so simple to just multiply the 3x value by 3 to show 9x...it makes sense though.
 
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 09:29
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Good find 8.  Thunbs Up  Guess that goes to show how important it is to be square behind your scope no matter what distance your at.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 11:02
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Originally posted by danjojoUSMC danjojoUSMC wrote:

8shots, did you test it with a few different scopes to see if it holds up? 
 
I've always read parallax error will increase with magnification, is it in the formula?
higher magnification-- it magnifies the error already there, doesn't increase it per se.
the parallax increases with increases in diameter or objective in the case of scopes
the refinement in the screw mechanism used to adjust for parallex becomes more difficult the greater the range, becomes more of a depth of field problem. (one of the reasons small diameter objectives) don't have ao.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2009 at 11:03
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Originally posted by supertool73 supertool73 wrote:

Good find 8.  Thunbs Up  Guess that goes to show how important it is to be square behind your scope no matter what distance your at.
absolutely!!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/08/2013 at 21:46
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What is the best method to adjust for parallax error if there is a mirage running?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 00:49
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A couple of comments:
- Where did you exactly dig this up?
- I need to think about it a little, but offhand I would say that these calculations are likely not applicable to riflescopes.

I would really like to see how the person who came up with these formulas compensated for focal length differences in different scopes and how those pertain to actual reticle size and focal point errors.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 06:10
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Get Your Popcorn Ready.....Glad I'm smart enough to stay out of this one!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 08:13
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I'm with Stickbow on this one.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 09:23
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ILya will identify the truth!
 
Wouter I thought you had lost interest in Optics. Wink
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 09:33
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Those posts are from 2009.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 09:40
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Whow...totally missed the date wouter posted the chart...
 
 
How observant of me!!! Loco
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 09:41
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ILya,

I started a thread about this equation in 2011, after reading this article:

Rimfire benchrest parallax article

No matter what, parallax error is mitigated by properly keeping your eye's axis centered in the exit pupil.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 10:16
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Originally posted by Bitterroot Bulls Bitterroot Bulls wrote:

ILya,

I started a thread about this equation in 2011, after reading this article:

Rimfire benchrest parallax article

No matter what, parallax error is mitigated by properly keeping your eye's axis centered in the exit pupil.

Yikes.  I did not notice this is from 2009.

I'll need to look through that link.

Bottom line though is that I have a hunch that the calculation is wrong.  I played with this some time back when I had a bunch of similarly configured scopes with adjustable parallax that I was testing for an article.  I had them all set parallax free at 100 yards and then looked at parallax error at various distances without messing with the side focus.  It varied from scope to scope and not insignificantly.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 10:29
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Sometime back, author's name omitted, I read an article in a highly touted gun magazine that said "you have to be certain to ensure the parallax setting is set on the proper distance, ie., 100 for 100 yards, 200 for 200 yards, etc, to ensure it is properly adjusted.  I threw the magazine away and have not picked one of those up since.  I've never found the parallax adjustments on any scope, including my Hensoldt, to be very close to the distance dial adjustment.  If it ever is, it is an accident.  Someone's eyes may match those dials, but mine sure don't...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 12:30
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It may be 2009, but still misunderstood. How are you guys adjusting for parallax with mirage running?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 12:50
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I have found the best solution with what we are talking about as far as parallax goes is the one on my Premier,there are no numbers.I thought I could resist jumping in but my stupidity got the best of me.....Stop laughing BUD Whacko
 
PS:
     Hows your mom feeling?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 13:10
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Longranger:
    Mirage has nothing to do with Parallax. It is a function of scope design and eye position. Mirage is external of the scope.

The cause of Mirage (Wikipedia)
Cold air is more dense than warm air and has therefore a greater refractive index. As light passes from colder air across a sharp boundary to significantly warmer air, the light rays bend away from the direction of the temperature gradient. When light rays pass from hotter to cooler, they bend toward the direction of the gradient. If the air near the ground is warmer than that higher up, the light ray bends in a concave, upward trajectory.

Once the rays reach the viewer’s eye, the visual cortex interprets it as if it traces back along a perfectly straight "line of sight". This line is however at a tangent to the path the ray takes at the point it reaches the eye. The result is that an "inferior image" of the sky above appears on the ground. The viewer may incorrectly interpret this sight as water which is reflecting the sky, which is, to the brain, a more reasonable and common occurrence.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 13:21
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Originally posted by stickbow46 stickbow46 wrote:

I have found the best solution with what we are talking about as far as parallax goes is the one on my Premier,there are no numbers.I thought I could resist jumping in but my stupidity got the best of me.....Stop laughing BUD Whacko
 
PS:
     Hows your mom feeling?
 thanks for asking.... She finally broke loose late yesterday and feels much btter.  CT scans show no absesses so she should be going home from the hospital Friday.  meanwhile we (me and my siblings) are giving her hell over being such a prude.  She was lamenting over having this hansome male nurse give her a sponge bath.... She asked for a different nurse. SO we all called the nurses station and got the nurses involved.  The male nurse showed up to bath her carrying flowers candles and body lotion....  the funeral should be next week.
 
At least we took her mind off her problems...  Yes it does run in the family... Bucky
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 13:59
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Hi 3_tens,
Please advise, I have always focused the crosshairs on the target first for clarity, then for movement of the crosshair on the target image.

If that image is moving with mirage I cannot get true clarity and as there is no stability of image, I cannot tell whether it is the crosshair or the target that is on the move.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 15:37
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First focus the crosshair to your eye. Look at the sky or a and adjust. Look away and back and adjust again. Repeat several times untill the reticle is in perfect focus when you first look into the scope. After the reticle is adjusted properly then focus the paralax adjustment to the target. Both the target and reticle should be in perfect focus. You need to be sure to keep a good cheek weld so that your eye stays directly in line behind the scope.
Got to the F.A.Q.   http://www.opticstalk.com/what-exactly-is-parallax-anyway_topic5026.html
A good description of Parallax.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/10/2013 at 10:44
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I can't remember ever seeing a paralax error/issue.  is that possible or was I just not paying attention?

 

just to clarify... paralax error is when you move your head and either the reticle seems to move or the target seems to move?

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