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Old April 12, 2014, 02:34 PM   #1
rebs
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parallax question

if your rifle scope has a factory parallax setting of 100 yds, what will the affect be at 50 yds, 200yds and 300 yds ? Is a parallax adjustable scope a necessity for those ranges ?
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Old April 12, 2014, 04:19 PM   #2
Chuck Dye
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This article pretty much covers it:

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

The TFL search engine will bring you a great deal.
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Old April 12, 2014, 04:40 PM   #3
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First, I don't think anyone has ever calibrated how much potential parallex error may occur at any ranges.

Last, sight through the opitical center of your scope and there will be no parallex error at any range.
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Old April 13, 2014, 01:12 PM   #4
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Thanks guys for the help, I book marked that article so I can return to it if needed.
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Old April 14, 2014, 09:17 AM   #5
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Scopes do not have a parallax setting. If they did, then parallax would never be zero when the aiming eye's on the optical axis of the scope.

Scopes "focus" the target image in the reticule plane by moving at least one lens element back and forth; just like camera lenses do when focusing subject matter on the image sensor.

Companies that claim their scopes have parallax settings must not think their customers are smart enough to figure all of this out. Or maybe they're not smart enough to figure that out themselves.
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Old April 14, 2014, 09:38 AM   #6
Brian Pfleuger
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That could well be, Bart, but it sure is universal. Every single firearms optics company that I've ever checked calls it parallax, and apparently have for many decades. This includes Nightforce, Leupold, Minox, US Optics, Vortex and many others.

It reminds me a little of the "Case Headspace" argument.
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Old April 14, 2014, 10:17 AM   #7
Bart B.
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It's not universal; some do, others don't.

A rifle scope company rep at a gun show years ago told me this "parallax adjustment" was instituted by a few high-end scope companies because most of their customers couldn't relate/understand the simple fact that binoculars, telescopes, rifles scopes, spotting scopes, microscopes and camera lenses all "focus" some down range image the same way at the back end of the optical system where it's viewed through an eyepiece that focuses the human eye on where it's focused by all the lenses in front of it. But because so darned many scope companies got frustrated with their customers not understanding (mostly because company reps lacked the wherewithall to explain it in simple grade school English and terminology), they "bowed" to consumer's inability to grasp the simplicity of it. Other companies followed, but not all of them.

When a rifle scope's not focused at the target range, there'll be no parallax when the aiming eye's the optical center of the scope. And when the scope's not focused at target range, but instead a long ways off, the target image will never be sharp and clear regardless of where the aiming eye is.

Perhaps the "adjustable parallax" folks should get together and convince the makers of military binoculars with a spotting grid scale in one side to call that center wheel adjustment on them the "parallax adjustment" instead of focusing. These optical devices work the same way and if not focused at the target range, there'll be parallax with an off-center eye on the scaled half.

Rant off.................

Last edited by Bart B.; April 14, 2014 at 10:50 AM.
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Old April 14, 2014, 11:10 AM   #8
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Quote:
First, I don't think anyone has ever calibrated how much potential parallex error may occur at any ranges.

Last, sight through the opitical center of your scope and there will be no parallex error at any range.
Calibrating parallax: I have. Its very easy to do. Just set up a 1" (or whatever size) grid on plain paper. set your rifle & scope up on sandbags & "wobble the eye" recording how many grid lines are moved across at your preferred offset distance.

Optical center: Has absolutely nothing to do with parallax. Parallax is the difference, measured radially between the offset of the reticule in the 2nd plane plane of focus & the image of the target in the 1st plane of focus.

Adjustable Objectives allow the 2 planes of focus (one from the front, objective lens) & the second (where the reticule is focused with the eyepiece) to be longitudinally made coincident, removing the seeming "drift" of parallax.
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Old April 14, 2014, 01:12 PM   #9
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Wogpotter, my scopes have a target image focused in both the first and second image planes and their reticules are fixed and immovable in the second plane. The aiming point on the target image is never centered on the optical axis at the first image plane. But that aiming point's image is centered on the reticule's image plane. Does all that seem right?

A scopes optical axis is a line between the objective and eyepiece lens' centers where second plane reticule is centered on. With the scope focused at some range other than target range and the eye is aligned with the scopes optical center, there will be no parallax. If the eye's off that optical axis, there will be parallax.

Last edited by Bart B.; April 14, 2014 at 03:18 PM.
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Old April 14, 2014, 08:04 PM   #10
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From Leupolds owners manual.

Quote:
Maximum parallax occurs when your eye is
at the very edge of the exit pupil (Even in this unlikely event, our
4x hunting scope focused for 150 yards has a maximum error of
only 8/10ths of an inch at 500 yards). At short distances, effects
of parallax do not affect accuracy (using the same 4x scope at 100
yards, the maximum error is less than 2/10ths of an inch ). It is
also good to remember that, as long as you are sighting straight
through the middle of the scope, or close to it, parallax will have
very little effect on accuracy.
The entire manual can be seen here.

http://www.leupold.com/wp-content/up...ope_Manual.pdf

Parallax is one of those things we probably worry about more than we need to.
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Old April 14, 2014, 08:32 PM   #11
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Jmr40 very interesting post, I bet the error goes up with power. Be interested to see the same info for a 24x scope
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Old April 15, 2014, 09:50 AM   #12
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I think you're saying the same thing as me but worded differently.
To focus in both planes the 2 planes must match, otherwise there is an impossible setup.

Regarding optical center I think there is a misunderstanding of which term we're using how. Optical centering means setting up the scope to place the center of curvature of the objective lens in the cross-hairs. This has the advantages of maximum adjustment in both axises & the best optical performance from the front (objective) lens groups.

Centering your eye at the exit pupil will minimize parallax, but it is not "optical centering", just looking through the middle of the eyepiece. The whole point to an AO system is to remove the "movement" perceived at the eyepiece by having the 2 planes match so it doesn't matter if your eye is a tad off center.
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Old July 11, 2015, 01:38 PM   #13
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Parallax and purchasing Leupold VX-1 scopes

I thought I screwed up a scope purchase. NOPE! I am now shooting a cheap Benjamin Discover PCP airgun at short to medium distances...150 ft max and I bought a long range scope. AAKK...AAKK...AK AK AK. I favor lightness and clarity because I'm shooting with my weak and slightly double vision eye. It has a little bit of old age cataract...so night vision is dimmer.

After much reading and thinking I see a general "communication" problem. Gunners don't talk optics language very well.

OK...this is it: I believe so called "scope-parallax" is actually error related to "depth of field". The depth of field is related to the optical system and I'll bet some are better than others. Some are deep and some are not. So...the center of the depth of field for say "Leupold" is set at a particular distance and can't be changed. Everything within that field of vision will be clear...but what about "eye relief"...is that a function of this internal depth-of-field?

So, I say if you can't get ever get a clear reticule and a clear target simultaneously you either need more depth of field or you need to move it appropriately. In photography one way is to "stop down" the lens to a smaller "f-stop"...from say f-1.8 to f-16. Then everything is sharp. You only use the best part of the optical axis...the center part. That's consistent with advice from gunners. Put your eye in the center of the "eye relief cone". It must be a cone of some kind.

In a gun-scope what exactly is this depth of field...eye relief??? Nobody ever says. Furthermore...you can't always change it. But do you need to? On a Leopold you can't...and you can't stop down the lens. AK Ak!

Well, today I got a VX-1 3-9x 40 mm and despite its parallax at 150 yards or so I can focus close in...20 ft and both reticule and object are OK for me...crisp enough to hit a mouse...that's for sure.

The quick theoretical fix is to compromise-focus...so both target and reticule are a bit blurry. Well, the cheapo Leopold VX-1 I got is SO good that whatever blur is more "ME" than the scope especially at low power. I really don't see ENOUGH double lines or edge blur to worry about, even with my weak eye. 6 months ago my eyes were so bad after a day of designing graphics on a computer screen that dashed pavement lines seem to rise up to hood level in my car.

I'll bet some of the problems with parallax come from using short eye relief and not putting your eyeball in the center or using it consistently because you don't even get to the same position for each shot....hence big groupings even with good equipment.

I believe the center of the cone of eye relief can be found and used as if you stopped down the lens. Simply use a cheek rest...a "cheek riser" and put it on your cheek in the same place each time where the blur is least.

I think that's why you get folks moan that the target and the reticule dot can be made to orbit by moving your head and why folks try and cure it with an Adjustible Objective. I guess for quick shots...it's critical....no time for a "set shot".

Less meds, more leutine and a dash of Leupold please...

Poor-Conoscoper...ex-student optical microscopist, photogrammetrist, professional Alaska field geologist, pseudo civil engineer, US Army Junior NRA and late in life NRA life member and handgun killer of squirrels lately...with a Crosman 600. yours truly, "Bears-once-feared-me"...johnson....(who tried to grow up in Alaska...and didn't).
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Old July 12, 2015, 11:43 AM   #14
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Quote:
"depth of field"
Right idea, wrong conjugate.
"Depth of FOCUS" is internal to an optic, "Depth of FIELD" is out there in the air at the subject.
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Old July 12, 2015, 03:20 PM   #15
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Parallax

REBS:
If you are experiencing parallax to the point that it is affecting grouping, there is a temporary field-expedient method to fix it...Provided the rifle is not a hard-kicking one.
As you move your head (either vertically or laterally) and notice an image shift, if you move your eye (either straight forward or back) a slight amount, you will notice the periphery... The outer edges in the image...darken and close in toward the center. Whichever way you move, either in, or out, (to a certain point) the image will [stabilize] and parallax will be eliminated, allowing you to focus your aim on target without any misalignment of the crosshairs on the bull/target, or any side-to-side/up-down movement.
This is ONLY a temporary, field-expedient measure using very light-kicking rifles, [I've used this on .22RF thru light-moderate loads in my .243 Win.] until I replaced the scope. A little experimenting with the eye movement might be necessary until you get the hang of it.

Just offering my humble $.02 input.

WILL.
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Old July 13, 2015, 06:16 AM   #16
rebs
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thank you guys for all the answers and help.
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Old July 13, 2015, 06:03 PM   #17
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virtual image vs real image versus ?

I'm thinking ray diagrams....and cheapness versus expensive optics.

So long low curvature glass (leopold) gives relatively parallel internal rays paths..(long ray cones). They but, if I'm correct, short high curvature glass (UTG compact?) gives pretty short high angle cones converging internal to the scope and if you don't have vernier adjustment wheels...well...you might never get decent image edges.

I suppose, with relatively high angle ray paths making your optical ray path cones you get much less depth of focus. The fat cones move your image quickly compared to the threads of your focus wheel. Your knob moves fat cones a lot as you turn the knob just a little. It's like imagining an optical inclined plane. You get blur when you move the knob too much and your (my) old eye lenses can't re-bend incoming scope rays at high angle to rest on one part of your retina to get a sharp edge signal to your brain. You blur and focus and re-blur and the scope is impossible to hold or use.

That suggests old eyes should like long scopes, assuming the thread count on the focus screws are held constant.

What is this depth of focus...this eye relief thing but a MEASURE of something unsaid. I can't put common words on it but the size of the exit pupil...and the length of the eye relief must be a cone of some kind that reflects a compromise...I'm guessing.

So...large exit pupils and long parallel rays give a pistol scope or a scout scope...I guess. So what's the tradeoff to get a pistol scope and if you use it as a "scout" scope...what then? I might try and put a "scout scope" on a pistol but so far...it looks like I'd be wasting my time.

I wanna scope for my mod'd 1389 .22 air carbine that works OK if I take off the stock and use it as a pistol and if I want...I can put it on my other Benjamin PCP rifle...a .177 for grins and shoot varmit.
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Old July 14, 2015, 07:45 AM   #18
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Long paths are better just because the "Circle of confusion" is further away from the "Circle of least confusion".
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Old July 14, 2015, 09:17 AM   #19
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If your cheek weld to the stock is very consistent you'll have virtually no parallax problems. It doesn't happen unless you're moving your head around when shooting.
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