I want to buy an Aimpoint 3X for use with my T1. However, I find it hard to believe that this could be a good idea.
Any time light passes through a glass surface, the beam will shift a certain amount. It is just physics. The flatness and angle of the glass can make it worse. However, the light always bends. there must be several pieces of glass in this optic. The only way around this is to have an adjustable compensation wedge in the device and fine tune each magnifier with a laser so that … POI light in = POI light out. I don’t see any way around this.
When you put the magnifier in place, how much does it shift the POI? Has this been discussed in other threads?
Short answer- the is no “true” shift in POI when a magnifier or optical device is placed behind the sighting device. There may be some pervceived shift simply because the shooter zeroed unaided, in which case the apparent size of the target and reticle was less well defined.
Long answer-
Some shooters have reported having a slight shift in zero when checking zero with the magnifier (due to the above reason), but once the sights are tweaked to provide a more precise zero that zero will remain true even without the magnifier- thus proving that it is not the equipment but rather the shooter’s perception that was lacking precision.
The image entering the 3X is what will be magnified. The light entering is basically 2 dimensional (very simplistic explaination, but I am not a physicist by any stretch of the imagination). Imagine that the target is a print on a piece of paper. Draw a dot on the target- that is your aimpoint dot. Hold a magnifying glass between your eye and the image- this is your magnifier. No matter how much the magnifying device distorts the image, the dot is still in the same relationship with the target.
The problem is when an optical device is placed in front of the sighting system. Once that happens the true image that arrives at the front lense is not necessarily in the same relationship to the front lense as when the optic was zeroed, in which case the POI shift may range from minor to extreme.
There are some device that can be placed in front of an optic and exhibit very little shift in POI, but they are very specialized and expensive pieces of kit.
If you zero the weapon with the magnifier installed, the most accurate POI is established. when you remove the magnifier, the POI shift is less than the size of the red dot anyway. at least, this has been my experience.
what you realize is that you weren’t perfectly zeroed with the unmagnified 4MOA dot in the first place.
in the first example with a magnifying glass, perform this experiment: look through the magnifying glass at the dot you just drew, and move the magnifying glass without moving your eye/head. doesn’t matter if you rotate it out of plane or just translate it. the dot will move, even though your eye to dot relationship hasn’t changed. the position of the dot changes depending on where you put the magnifier. do that with prescription eyeglasses, too. move them up and down a few inches in front of your eye and you’ll see the image (dot) move as well.
the same problem occurs when you place an optical device behind the sighting system as in front of it. the image leaving the optic to your eye might not be in the same relationship than if it weren’t there.
that’s why in some cheap scopes with variable power, you’ll see a POI shift when you change magnification. the reticle hasn’t changed - it’s still mechanically zeroed. what changes is what your eye sees, and the optical image of the reticle relative to the target.
the bottom line (as i see it), is that any medium placed between your eye and an optic can change it as light passes through. how much depends on the quality of the glass and alignment of the lenses, mount, system etc. theoretically, there should be no POI shift when putting a perfect magnifier perfectly aligned behind a red dot. but practically, it can happen due to manufacturing tolerances in the optic and mount. if the magnifier is used during zero, and is left on there, it doesn’t matter if it’s never removed since the error will always be the same, and is included in the zero. but taking it on and off will apply whatever error there is.
as others have mentioned, there’s also change in the perception of the shape of the dot when magnified and not, so there’s human sighting error involved as well. it’s just my .02 that POI shifts are not 100% attributed to human sighting error, but there are mechanical/optical influences as well. that’s why good quality optics with properly aligned lenses (and good mounts) make a difference, even with magnifiers.
I think F2S’s point (and please correct me if I’m wrong) is that it doesn’t matter if there is some tiny difference in alignment between the RDS and your eye when seen through the magnifier. Why? Because the relationship of the dot to the target remains constant. You could be looking through the RDS using a periscope, you’d still be aiming properly.
In other words, no matter how much you shift the image after it comes out the end of the RDS, the RDS doesn’t change alignment.
It’s completely different than a variable optic, especially if the red dot is projected behind the magnification lenses.
Actually, Militarymoron nailed it. Any time you place a piece of glass in the optical path, a shift will occur.
The system can be calibrated with or without the glass. BUT, not both. The issue is how to make the shift small. Flat optics completely normal to the beam help. But, there will be shift as it is inserted and removed.
If you zero your RDS and then insert the magnifier, your eye will perceive a false location of the red dot and an error will occur. You aim based on the light that reaches your eye and is now shifted from it’s original position.
todd, i understand what you’re saying, and my point is that while the dot to target relationship may remain constant, putting a lens in between that dot and your eye can change the image that you see.
just do that experiment with a handheld magnifying glass and target and you’ll see. the dot to target relationship doesn’t change, but the image of the dot can move, causing you to re-adjust the dot to place it over the target based on the image you see.
again, i’m not talking about the RDS changing aligment, but the RDS image that your EYE sees. it’s like shooting a fish with an arrow in water. the relationship of the fish and you is the same, but the image of the fish you see is not its true position, which is why you have to aim off.
bouncing light off good quality first-surface mirrors as in a periscope is different from light passing through a lens.
we’re talking about very small amounts here, with magnifiers and a RDS. for the most part, most of us won’t be able to notice a POI shift practically. i always get jumped on for saying that there can be a POI shift when looking through a magnifier, and my intention is not to scare people off them at all. some people do experience shifts, but everyone points to the user as the source of the error. some of it may be, but i believe that not all of it is.
all i’m saying is that where you point the gun depends on what your eye sees, which can be altered when something is put between it and your aiming device, that ‘might (however small)’ change that image.
edited to add: i posted this before i read the response above. when gjj says that a shift will occur, it doesn’t mean that the shift is perceptible nor has any practical effect. it could be a 0.0001 MOA shift, or it could be enough to affect POI, depending on the quality of the optical medium you’re looking through.
i must clarify that i’m an engineer (sorry - very anal retentive) and think in very ‘black and white’ terms when a question is asked. to me, an imperceptible shift that is measurable (with instruments) but not with the human eye and has no practical effect on POI is still considered a shift. physics is black and white, and doesn’t differentiate between the theoretical and practical.
jumping on to what gjj said - the key is to make the shift unnoticeable, by ensuring proper alignment and quality of the optical medium so that it does not change the alignment of the image seen by the eye from its true position.
From what I am reading at a variety of different sources, the most common answer is about 1.0" to 1.5" of shift when inserting the magnifier into the optical path.
This will kill it for me. I wanted to use this as an optic for coyote hunting in the desert. The kill zone is about a 6" circle. Even if I zero with the magnifier in place, I don’t want to suffer that type of shift close up. I will continue to use my traditional scope.
For man size targets, I don’t think it would be a big deal.
LOL - i guess ‘practically’ depends on the person/need
for me, i can’t shoot well enough offhand to notice any shift.
anyways, you might try one and if you do see a shift, sell it.
The shift is not an issue in my experience. I’ve used my ML3(2 MOA) and LaRue Po-Boy setup to successfully engage 6" and 8" steel plates at 330 yards. YMMV
Could you elaborate a little on dot shift after the optic.
I am sincerely asking for more informaiton/clarification. The last time I dealt with light physics was about 13 years ago.
Here is what I understand, and if I am wrong, please correct me-
With a collimated dot optic as long as the dot is relatively near the optical center of the optic there will be no shift in POI. I undestand that when the dot is near the extreme of the visible area there will be a slight POI shift. The image entering the objective lens will have the dot superimposed on POI (when at the zeroed distance) on the target. That image will be constant since any distortion caused after the image leaves the occular lens will distort the entire image, not just the dot. This is of course assuming that parallax is correct.
What I am not grasping is how any device placed between the occular lens and the eye can cause the dot to shift on the target without equally shifting the image that the dot is superimposed onto, unless there is parallax error with the optic itself.
F2S - putting a lens behind the optic can change the relationship of the dot to the target of the image. it’s not like changing the image of a 2-dimensional image like a photograph in one plane. the dot, while visually superimposed on the target, is not on the same physical plane as the target (different distance from the lens) - say, 1" instead of 100 yds., unlike a laser dot projected onto a target.
try this experiment with a pair of prescription glasses held about 6 inches in front of your face - hold your finger up between your eye and some point of reference. without moving your finger, look through the glasses and move them around. you’ll see the finger move in relation to the target, even though it’s still in line with your eye and the target. essentially, the image you’re seeing has changed even though the eye-finger-target relationship hasn’t. this is just to demonstrate how a 3-dimensional image can change (as opposed to a 2-dimensional one) due to a lens. with a RDS, the dot is ‘practically’ parallex free (not 100% parallex free in terms of black and white), so unlike the finger, it should remain on the target. however, that tiny, tiny amount combined with a lens that is not optically 100% distortion free, can account for that miniscule change (that you might not notice at all). let me know if that kinda makes sense.
Thanks for the explaination.
Unfortunately I do not have a pair of prescription glasses or a magnifying lens handy, but I will try it out as soon as I can.
Take a pair of normal sunglasses. Hold them away from your face and look at a spot a couple feet away. Remove the glasses. The spot will appear to move. Put the glasses in / take them out. The spot moves.
Now, hold the glasses away from your face. Look through them at a spot. Slightly tilt the glasses back and forth. The spot will move.
This is a worst case scenario because your glasses have curvature. But, it shows the principle. Optics can shift the apparent location of a spot.
Chen,
The Aimpoint 3X has always possessed the same “adjustments” as the new EO 3X. Not understanding what is so new about it?
Et al,
Great discussion and information regarding the use of a magnifier with a red dot sight. FWIW I have shot 11"X19" steel targets at 600yards with an Aimpoint Micro T-1 and Aimpoint 3X Magnifier. As mentioned I recommend zeroing the Aimpoint sight while using the 3X Magnifier as it will eliminate an perceived when the magnifier is mounted.
Not to beat this thing to death. But, if you zero with the magnifier in place, you will see a different optical path when you use it without the magnifier and have a certain amount of shift.
again, that shift may or may not be noticeable. let me summarize what i’ve always believed on this subject, and this is just MHO:
in a perfect world with perfect manufacturing, a magnifier will not change or shift the dot. physics states that when light passes from one medium to another, the light will be affected (which is what is going on when the image is magnified). however, you can obviously design the magnifier so that it magnifies the image while remaining optically ‘transparent’, and not affect the position of the dot. so, if the magnifier and mount are manufactured perfectly and perfectly lined up, there won’t be a shift.
everything is manufactured to a tolerance. nothing is ‘perfect’. the key is to make the tolerance small enough so that it falls within the noticeable/practical requirements of the user. in other words, while it may not be ‘perfect’, the user may not notice that imperfection/error. it costs money to make things well. if i ask people here “hey, why shouldn’t i buy a cheap chinese magnifier instead of an aimpoint if the clarity is good and it holds up?” i’m sure i’ll get some responses saying that you could get a POI shift because of alignment of lenses etc.
no manufacturer is going to claim that they manufacture perfect products. neither are perfect products needed.
so, the shift or difference that people might see isn’t because that the concept of putting a magnifier behind a RDS is flawed, it’s because of the stackup of manufacturing tolerances in optic and mount that may contribute to a slight optical error that produces a shift in the dot relative to the target. that, plus the difference in perception of the dot (which FJB has mentioned in the past), are factors that can contribute to it. some may see a shift, some may not. if you don’t see one, that’s great. if you do, then those are the two factors that i believe are contributing to it.
