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Parallax and hunting

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/12/2011 at 20:57
Bitterroot Bulls View Drop Down
Optics Master Extraordinaire
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Another thread got me to thinking again about parallax adjustment and its necessity in a hunting scope.  I recently changed a scope on a hunting setup from a tactical style side-parallax adjustable scope to a hunting-specific non-PA ballistic reticle hunting scope.

The lack of parallax adjustment was a feature I was looking for.  I just seem to mess with the parallax adjustment too much in the field.  I also thought that by keeping my eye centered behind the exit pupil, I could minimize the error.

Well I read a very interesting thread here:

http://rimfirebenchrest.com/articles/parallax.html

The author walks throught he math, and comes to a simple equation for calculating Maximum Parallax Error (MPE).  I began running some numbers through the equation and the results were interesting.  The equation goes like this:

Maximum parallax error (in mm) at X yards =0.5(objective diameter in mm)(ABS(X-scope's parallax setting in yards)/scope's parallax setting in yards

In the other thread, posters were interested in the Minox 3-15X42 ZA3 riflescope, but were concerned about the lack of parallax adjustment.  So lets say you want to know what the maximum parallax error of that scope would be at 600 yards.  Minox's website lists the factory parallax setting  for the scope at 100 yards.  We will plug in the numbers:

MPE = 0.5(42)(600-100)/100

MPE = 105 mm or 4.13 inches or .65 MOA

And that is the MAXIMUM error.  It is the amount of error introduced if your eye is in line with the very edge of the exit pupil.  And that amount of error decreases substantially as you get closer to the center of the exit pupil.

I understand that it is good to eliminate as many variables as you can for shooting, but that is a small amount of error for the hunter, even at long ranges.

It is interesting to note that this equation does not account for magnification, but it would stand to reason that it would be easier for a shooter to line up his eye more towards the edge of a smaller exit pupil than a larger one, so it would be easier to introduce parallax error in a small exit pupil compared to a larger one.

I think hunters get a little too concerned about parallax.  It is a different story with target/benchrest and tactical shooters.

What do you think?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/14/2011 at 07:32
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Parallex has always baffled me. I've had many scopes and haven't had a problem with parallex, but I do know and have watched where I place my cheek on my stock. I found that even if I move my head very slightly the sight picture will shift from side to side. The importance of having a consistant cheek weld when you shoot a string.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/14/2011 at 09:41
308 Sav View Drop Down
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I kind of agree, with exceptions. 

In your example of MPE = 105 mm or 4.13 inches or .65 MOA 

If I understand the math and and angles correctly. That is a plus or minus, because that is the max from point of aim in any direction. I.E. .65 left to .65 right, up or down. That in itself is over 8 inches at the 600 yards mark to ad to half your moa rifle.

In most normal hunting ranges it will not matter, but it is still important to long range hunters just as it is to long range paper punchers. With that said, I would prefer a hunting scope to have a preset parallax to have one less thing to adjust for a shot that time may be needed on. I hunt a short distances, less than 200 yards.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/14/2011 at 10:04
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Originally posted by 308 Sav 308 Sav wrote:

I kind of agree, with exceptions. 

In your example of MPE = 105 mm or 4.13 inches or .65 MOA 

If I understand the math and and angles correctly. That is a plus or minus, because that is the max from point of aim in any direction. I.E. .65 left to .65 right, up or down. That in itself is over 8 inches at the 600 yards mark to ad to half your moa rifle.

In most normal hunting ranges it will not matter, but it is still important to long range hunters just as it is to long range paper punchers. With that said, I would prefer a hunting scope to have a preset parallax to have one less thing to adjust for a shot that time may be needed on. I hunt a short distances, less than 200 yards.


Yes that is how I understand the error as well.  However, that is the maximum error with your eye at the edge of the exit pupil, which would be an awkward way to look through the scope and an inconvenient way to shoot.  So let's say your eye is halfway from the center of the exit pupil to the edge.  Then the error in each direction will be just two inches or so in any direction.  If you have your eye centered perfectly, there is no error at all.  I think most people naturally put their eye in the center of the exit pupil, which is why peep sights work so accurately.

Then you have scopes with parallax set at longer ranges, like my Swarovski 4-12X50.  It's factory parallax setting (for the BRH reticle model) is 219 yards.  So at 600 yards the MPE = 43.39 mm or 1.7 inches.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/14/2011 at 10:37
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This is very interesting. I have been baffled by Parallax, and have never read any explanation which didn't make things more complex for me. I am also considering the minox 3-15x42, as I prefer a smaller obj, and have wondered why the 42 obj has no side adj, and the 50 obj does.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2011 at 11:27
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I would be nice if a few more people who are really in the know would comment on this. 6" at 600 yards does not seem like alot considering that you would have to have bad eye placement, and that any shot that far would be a planned shot that would give the shooter time to align properly. I am talking about hunting applications, and not competitive shooting.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2011 at 14:16
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http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2555963#Post2555963
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2011 at 14:46
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Originally posted by coldhunt coldhunt wrote:

I would be nice if a few more people who are really in the know would comment on this.


ouch.

Ouch
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2011 at 14:53
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I for one do not understand parallax and choose not to; it is an ever-present excuse for bad results.  "My form is perfect, it's that damned parallax that caused the miss!"  Most other shooters don't understand parallax well enough to know that my shooting sucks, with or without proper parallax correction.

If you know all, your gear is awesome, and your form is perfect; a miss can be attributed to nothing other than parallax.

Or star mis-alignment.

Or a bad piece of brass.

Or a sudden drop in barometric pressure.

Or a temporary suspension of the laws of physics along my bullet trajectory.

Or a wormhole (which is entirely different than a suspension of physics.)

Or a loose base screw.

Or a calculus error made by my weather station (a rate of change of a rate of change, after all.)

Or a powder dispenser error beyond my control.

Or...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2011 at 16:47
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I only worry about it for my varmint rig (long range,small target) and on .22s when I have the power cranked up higher at short range to hit teeny targets.

For your average big game rifle scope, with less than 16x top magnification, it's not a big concern. DOF is sufficient at range that nothing ever goes out of focus too badly, and the max parallax error dwindles to insignificance compared with everything else that can send a shot awry.
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