GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: rdhj on August 31, 2014, 11:25:58 PM
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just learned about optically centering a scope using the method of laying the scope on a box with notches cut out of it and turning it. Figured while i wait for my new UTG for my nitro venom to show up in the mail, I would check to see how centered the UTG on my 22 LR is and it of course is not centered. now here is my question...knowing that this scope is zeroed in at 50, if I was to go and move the adjusters to optically center it, the scope would no longer be zeroed.....then when i go back to the ranged and resight back it, it should end back up on the same setting that I started with, correct. therefore, how would starting with optical zero help you in the first place? confused?
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You are confused. hopefully I can help. You want to keep the scope near optically centered mainly because it helps with springer recoil. A scope adjusted way off OC puts the springs holding the crosshairs in an uneven tension situation and allows them to move during the double recoil. OC is more ridgid. To me its much easier to center a scope using the "mirror" method. You can also tell which way your gun was shooting by looking at where the cross hairs are at using this method. The idea is to keep your scope OC and then align to barrel using adjustable mounts or bend your barrel to align to your scope. If the 2 are too far off it is difficult to avoid poi shift. Hope this helps.
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If you want to keep your scope optically centered, short of bending the barrel, the only practical way it to use adjustable rings for your coarse adjustment and then just fine tune with the turrets.... The optical clarity (aberrations) are less on the optical center, which is another advantage....
Bob
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Okay I'm very confused...
Couldn't you just turn the adjustment turret knobs clockwise until they max out in movement, then count how many clicks of adjustment they have in total turning them counter clockwise until they run out of adjustment in that direction and then just set each one in the middle?
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From what I understand ,no you cant because some scopes allow for more vertical adjustment in one direction and it may not be good for the scopes springs to be maxed out. you're sure to get it exactly right without possibly stretching your springs by putting it flat against a mirror and you'll see 2 sets of cross hairs. The shadowy one is the reflection and if its high right your poi is high right relative to OC. Adjust the turrents as you're looking through to easily achieve OC. What I do then is bend my barrel to match poi to poa. I've not found anything that makes me wrry about bending barrels,just the opposite. heres a target pistol.
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Carefully turning the scope to stops and then going to the center is a start to optically center the scope. You are actually compressing and decompressing the springs that hold the reticule in place and if you don't force anything, theoretically there should be no problem.
As mentioned before, once the scope is centered, the only way to get it on target without moving the adjustments is to use adjustable mounts.
What has not been mentioned is that when the scope is centered, if you have to adjust vertical for a distance change or horizontal for wind, the reticule will move more precisely only in the directions you adjust for.
In other words, when the scope is NOT optically centered, a vertical adjustment will also move the reticule slightly horizontal and vice versa. It may or may not be enough to make a difference but if you are trying to achieve pin point accuracy, it may be more difficult to achieve.
So the best thing would be if you had an optically centered scope and used the adjustable mounts to zero it in to POI.
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The techniques available to you to keep your scope optically centered are:
1. Bend the barrel
2. Use adjustable scope rings
3. Shim the scope (the dovetail for windage, saddle for elevation)
The V-block method of centering that you mentioned in your original post is best. I wrote up a little summary in the thread about Sun adjustable rings linked in my signature. It's in a post near the end of the thread. Sorry, I would link to it directly but I am on my phone.
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I do not recommend using the turning to stops and counting turns method...I believe I have ruined 2 CP 4-16X40 scopes trying that...
many here give a decent review of that scope but I had bad luck holding point of aim....twice
it seems to me that there is no "hard" stop at the loose end of the adjustment, you can feel the tension slacking off and eventually you hit a sort of snugging up like a nut riding over a slightly distorted thread but nothing like the slamming on of the brakes you are there feeling at the tight end of the movement...
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Agree about using the v block method; it is quick and precise. The mirror method is only valid if the objective bell surface is PERFECTLY square to the bore of the scope. I would bet most scopes, especially less expensive ones have some degree of misalignment here. V block is foolproof, the tweak the barrel to adjust POA. Simple, tk
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From what I understand ,no you cant because some scopes allow for more vertical adjustment in one direction and it may not be good for the scopes springs to be maxed out. you're sure to get it exactly right without possibly stretching your springs by putting it flat against a mirror and you'll see 2 sets of cross hairs. The shadowy one is the reflection and if its high right your poi is high right relative to OC. Adjust the turrents as you're looking through to easily achieve OC. What I do then is bend my barrel to match poi to poa. I've not found anything that makes me wrry about bending barrels,just the opposite. heres a target pistol.
That pistol must be extremely accurate.... ;D
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I've personally found the v-block method to be a pain. I used to do that. The block method may theoretically get you more percise but that little bit deosn't matter at all with your set-up.
And short of spending maybe 50 % of what the N. V. costs on adjustable mounts , you could bend the barrel. I've found adjustable mounts to have there own problems as well.
1. Something else that can go wrong ( esp. with springers )
2. Cost. You have an N. V.
3. Scope height. I like mine close to the barrel. Thats just me though.
4. Avaliability. You can literally go out to your garage ( or back yard tree ) and bend it.
5. I have not found one good reason not to , at least on an unshrouded springer.
And as mentioned above you could shim the mount, or scope rings I should say. Although this can be done for slight vertical adjustment , much can go wrong with this method (like bent scope tube due to poor seating of the scope) , and you can find tuners who recomend against it. Again, esp on springers. Adjusting the windage with the scope rail? What a PITA that would be. On a one piece mount maybe but why do it on a N.V. when you have an easier, more sound solution?
I mean you could take it to a machine shop and have the parts re-made in perfect alignment but why not tell people how effective and easy and free it is to use the barrel bending tutorial found on this site? I did, and my 70$ adjustable mount is now on the shelf. The next 2 times I did it I used the the tree fork method to bend that a gentelmen on here said he used. Results . Thats what I got.
I sense sarcasm in your post f4milytime. You will find if you research that many top manufactures and tuners bend barrels. I'm no expert , so all I can do is seek expert advise. I've read every post by rsterne , my A G exemplar. So there's that....
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I went through this a while back, and decided to shim the scope rings for optical center. I gained my wisdom from the internet and used thin aluminum shims from the side of a soda can. DON'T DO WHAT I DID! I got away with it on two scopes, but I crushed the tube on the third, thankfully not to the degree that I ruined the scope.
I was later advised by an airgun veteran that old film negatives make much better shims and won't damage tour scope. He also showed me a $17 adjustable mount made by Hawke that negates the need for shims in the vertical.
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Vee block veteran here. Easy and as accurate as "I" can be. ;)
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6. You can leave the scope in the rings with the mirror method.
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The mirror method is useless if the objective bell of the scope is not perfectly at 90* to the centerline of the scope.... I have several scopes here of different brands and prices where that is NOT the case, and the worst one is off 0.020' on a 2" diameter, which works out to an error of 1 yard at 100 yards or 36 MOA....
The image in the mirror would be TWICE that far out of adjustment.... Of course some scopes have an angled sunshade on the front and can't use the mirror method at all.... I would NOT recommend using a mirror on the objective bell to try and optically center a scope, either count clicks (close enough, I use that and have never had an issue) or best, use the "V" blocks.... You can save a LOT of time by turning the scope 180* to get one turret correct, then rotate it 90*, again turning it 180* to get the other turret correct....
Bob
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does this idea of optically centering scopes and using adjustable mounts to zero the reticle really only apply to air gunners or do shooters of regular firearms also do this? I never did this for my other 22 LR savage that has a nikon P22 scope on it and the windage is centered all the way out to 100 yards as far as I can tell.
Also...what makes the windage off at other yardages on a not optically centered scope...to me, i dont see how anything should change....the vertical reticle line is still in the same place in the scope and the pellet is still coming out of the barrel in the same place windage wise
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does this idea of optically centering scopes and using adjustable mounts to zero the reticle really only apply to air gunners or do shooters of regular firearms also do this?
I am interested in hearing what others have to say on the subject but one reason it affects air guns more is the relatively short range at which they are typically zeroed. Invariably there is some slight misalignment which causes the barrel and the scope to point in slightly divergent directions.
For the sake of discussion, let's say they diverge in the lateral direction (i.e windage). When you then zero your rifle, what you are doing is making them intersect at a single point off in the distance. If that distance was 25 yards, then at shorter range the pellet will impact to one side and at further range it will criss-cross to the other side.
The shorter the zero range, the more aggressive this compensation must be and therefore the more pronounced the effect will be. That's why it is good to adjust your windage at the maximum range you can reliably group pellets.
The same is true of dealing with elevation associated with barrel droop. However as a practical matter, I find it less burdensome to compensate with elevation-related errors because dealing with a loopy trajectory is an inescapable requirement of shooting air guns. I just have to make a range card and use it but if my POI is wanding left to right before I've even given a thought to the wind, hitting the target just became a crippling math problem.
I set up my go-to rifle, a .22 cal QB78 HPA conversion shooting at about 32fpe, with adjustable mounts and it is dead nuts on the windage whether the shot is at 10 yards or 50 yards. With proper holdover and holdunder, it will nail the mark every time. Last Thursday I decided I wanted to check that the rifle was still zeroed properly. I hung the following target at 65 yards and with 2 mildots of holdover, fired two shots. I imagine it would have been humbling to do some groups but it satisfied my curiosity that the rifle was still zeroed. Plus I've learned when the first two shots look like that, it's time to put the top back on the tin and go back in the house with a smile on my face because it can only go downhill from there. ;D
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The mirror method is in no way useless to optically center a scope. Of course if you have a hood on your scope you cant use this method. For 99.9% of shooters it is way close enough to keep the cross hairs stable and close to center. The other .1% that need the cross hair closer to perfect optical center know how to do it I'm sure.
Those are interesting numbers you came up with from your worst case scenario scope but I question their accuracy. You claim the scope is 72 moa off? (36x2) Supposing the scope has 100 moa of total adjustment that would indeed be way off. And that would somehow appear lined up in the mirror? And you get this number by measuring the objective bells relationship to the centerline,projecting that out to 100 yards? You are very clever with math and no doubt far surpass my understanding of engineering. I am a freshman in college just starting on an engineering degree. I dont know squat , yet. But common sense tells me there is nothing wrong with the op using the mirror method.
And then there's this
From the Leupold Answer Guide.
Tim
Centering of a scope's adjustment dials
The elevation and windage adjustments of a scope are easily centered. Place a small mirror against the objective end of the scope. That would be the end farthest from your eye as you look through the scope. Make certain that the mirror is large enough to cover the entire objective. It must also be flat against the objective. With the scope's power selector ring set at the lowest magnification, look through the eyepiece as you would while aiming at a target. If the scope's windage and elevation adjustments are off center, you will see two images of the reticle (cross-hair). To reach the center of the adjustment range, simply turn the elevation and windage dials until you see only one image of the reticle.
I'm sure it's not the most precise method,like you say,but for the context in which the question was asked I feel like I gave a good answere and you came off as condescending. Kinda bothered me because I do read all your posts and highly respect your opinion.
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When I first made a V-block, I checked two scopes that I centered with the mirror method and found them to be off by quite a bit. Worst case was one turret needing to be adjusted by roughly 30 clicks (~8 MoA). The fact it can be done quickly and without removing the scope from the rifle is appealing for sure and it may well be good enough depending on the expectations of the individual. But like many things in life, the best way to do it is not the quickest or easiest. Fortunately a V-block is not a tool that must be purchased at great expense or built in a shop filled with precision machinery. One option is to cut V-shaped notches in a small cardboard box and use that...the main downside is that it is not easy to hold rigidly but a little creativity goes a long way. Load bricks in the box to anchor it, for example.
Regarding Leupold's recommendation to use a mirror, bear in mind that they cater primarily to users of centerfire rifles who will zero at 100 yards or more. An air rifle capable of shooting flat enough to be zeroed at that range can probably forgo the most precise centering method. Also, my guess is that Leupold's machining tolerances are better than most so perhaps a mirror would give comparable results.
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I have a small wooden box with 2 notches cut into it and its got a few thousand bb's in the bottom of it that I made for the v-notch method.
If a scope is off by 8 inches at 100 yards ( Your worse case scenario) then it would be off 4 inches at 50 and so on. Since every AG I 'm talking about will be zeroed less than 100 yards I'm not following your logic of " bear in mind that they cater primarily to users of centerfire rifles who will zero at 100 yards or more." But at least you got it down from 72 to 8 moa. Still I think op will be fine. But what do I know. You're the experts we come here to gain knowlege from. As long as no one gets blown up here we're fine,right?
Ok guys. There is no way you are going to convince "me" that you cant or shouldn't use the mirror method. I dont think you see the forest through the trees. So from now on I'll just come here to read.
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The mirror method will simply "ball park" the scope in my opinion:-) I use both methods. The mirror method to get me close, then I move in for the kill using the V-block method.
Someone here asked about this method of scope mounting on air guns verses regular powder burning firearms. Yes, it is used on powder burning rifles too. I think having the scope centered and perfectly aligned with the rifle bore is even more important on powder burning rifles, than it is on air guns.
Sadly, mass produced factory rifles often have errors with the scope mounts NOT being perfectly aligned with the bore. I've seen these errors on many mass produced rifles. Doesn't really matter what the brand name is. It's a shame when most air rifles today are built to better standards than many mass produced firearms.
Many hunters don't ever bother trying to "square" things up. They just slap on a scope, zero at 25 yards and go hunting. Heck, many hunters can't hit anything beyond 150 yards, and seldom ever try. They never realize the true benefit of having everything "squared" up, and just assume that everything is square, when in fact it isn't.
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Angles are angles, if you are studying engineering you should know that.... as I said, I have one scope (actually a Bushnell) where the end of the bell is 0.020" out of square with the side of the tube on a 2" diameter.... That is (0.020" / 2.00") x 100 yards = 1 yard or 36", so if you used the mirror method that would be the error in angle relative to the scope centerline.... I shouldn't have multiplied by two, however, that was incorrect.... Using a mirror to try and center THAT scope was useless.... I have other scopes where the bell is out of square between 0.003"-0.007", but on about 2/3rds of my scopes I can't measure any error, so using a mirror on those would work fine....
I apologize if you feel my answer is condescending, but all I'm trying to do is point out a problem with a method that is often quoted and does NOT work unless the scope objective housing (which is what you are putting the mirror against) is perfectly square with the centerline.... If you don't think it matters, center your scope using a mirror and then slide a piece of paper under one edge of the bell and I guarantee you will again see two reticles.... I discovered this quite by accident, published it as a warning here on the GTA about a year ago, and I have never seen anywhere else on the Internet it is mentioned.... Sometimes commonly accepted things have built in errors people just haven't noticed.... One of the benefits of Forums such as the GTA is the ability to pass on experiences that can dispel such (potential) myths....
Bob
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Apology accepted. You have bedazzled me yet again with your awesome AG jargon.
I still think your numbers are wrong but I'm not smart enough to prove it so I'll let it go.
A friend whom I was talking to about the fantastic world of airgunning (he wanted to know why I chose engineering) asked me what gun I would have if only I could have one in all the world. I just finished showing him pictures of the best ones I could find by keywording top airguns,most expensive airguns, etc.,and it hit me. If I could have any gun it would be the pumper you made with the lothar wather barrel,that beautiful stock, and amazing power. That thread was so interesting. Actually fascinating. The ones you have discussing qb"s (as well as nervoustrigger) are among my favorite as I have a jc higgins waiting to be converted to hpa.I literally have read everything you have written here and what I could find elsewhere.
This is my second week of my freshman year so I dont know jack yet. I've learned far more here than at school. Let it be known that my desire to make the things you make,to be more like you, is what led me to choose engineering. So thanks, and thanks gta.
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I've personally found the v-block method to be a pain. I used to do that. The block method may theoretically get you more percise but that little bit deosn't matter at all with your set-up.
And short of spending maybe 50 % of what the N. V. costs on adjustable mounts , you could bend the barrel. I've found adjustable mounts to have there own problems as well.
1. Something else that can go wrong ( esp. with springers )
2. Cost. You have an N. V.
3. Scope height. I like mine close to the barrel. Thats just me though.
4. Avaliability. You can literally go out to your garage ( or back yard tree ) and bend it.
5. I have not found one good reason not to , at least on an unshrouded springer.
And as mentioned above you could shim the mount, or scope rings I should say. Although this can be done for slight vertical adjustment , much can go wrong with this method (like bent scope tube due to poor seating of the scope) , and you can find tuners who recomend against it. Again, esp on springers. Adjusting the windage with the scope rail? What a PITA that would be. On a one piece mount maybe but why do it on a N.V. when you have an easier, more sound solution?
I mean you could take it to a machine shop and have the parts re-made in perfect alignment but why not tell people how effective and easy and free it is to use the barrel bending tutorial found on this site? I did, and my 70$ adjustable mount is now on the shelf. The next 2 times I did it I used the the tree fork method to bend that a gentelmen on here said he used. Results . Thats what I got.
I sense sarcasm in your post f4milytime. You will find if you research that many top manufactures and tuners bend barrels. I'm no expert , so all I can do is seek expert advise. I've read every post by rsterne , my A G exemplar. So there's that....
I'm talking about the picture of the pistol you posted.
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Noob question here, but how much of this thread would apply to a red dot? Would you see two dots in mirror if it not centered?
I have no idea what the internals in them looks like so thus the question.
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ok, so if i have this straight...one should optically center their scope as best they can, then mount it to the gun...go to the range and then zero it in....it should not take too many clicks to get it zeroed unless there is some kind of major issue such as barrel droop or misalignment somewhere.... to get the most accuracy you would want to leave the scope optically centered and use an adjustable mount on any gun to do you zeroing.....and i thought it was just as easy as buying a higher quality scope and sighting it in LOL
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You're on the right track now rdhj. Don't know what you're shooting, but start at the 10yd mark, just to see what she does. Don't start cranking on her yet...just use your Mildots for corrections. It may be waay low or high, but... Then move out to 15 yards, and see what she does. The 20 yard mark is a good place to start making turret adjustments to zero the scope. You can fine tune the zero point later,,,when you know your actual fps and pellet selection.
G'Luck to Ya ;)
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ok, so if i have this straight...one should optically center their scope as best they can, then mount it to the gun...go to the range and then zero it in....it should not take too many clicks to get it zeroed unless there is some kind of major issue such as barrel droop or misalignment somewhere.... to get the most accuracy you would want to leave the scope optically centered and use an adjustable mount on any gun to do you zeroing.....and i thought it was just as easy as buying a higher quality scope and sighting it in LOL
I still look at my rifle scopes and wonder why they have elevation and windage adjustments because they always move the reticle off of optical center, with adjustable scope rings you really don't have any need for 'em ever! Maybe the manufacturers are reading and will decide to produce a scope for the optical centering crowd. 'Purely Rhetorical' :P
BTW No one mentioned how to proper verify optical center after using the two methods posted ? Maybe I missed, didn't read the whole thread. Once you have optically centered the scope uninstalled, install the scope into the rings loosely (somewhat finger tight, but loose enough to rotate). Now carefully rotate the scope without banging the turrets against the receiver. Don't be surprised if optical center has moved, personally I'd use the mounted optical center over the unmounted optical center. U.S. Optics's use to have a video demonstating this method but I can't find it for a link. I'm still searching.
Here we go: http://vimeo.com/13563013 (http://vimeo.com/13563013) If I ever did optically center a rifle scope, this would be the only method? ;)
t
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Not sure if you realize it yet, but you are dancing around an alternative to the V-block. If you have a good way to hold your rifle steady (e.g. Gun vise), place the scope in the rings but leave them loose enough that the scope can spin freely.
Hello improvised v-block.
Just take care not to scuff up the scope tube as you rotate. Line the inside of the rings with masking tape temporarily to prevent that from happening.
Now you can go in reverse and use a V-block to verify your results (just kidding...no reason to do that unless it just helps you sleep better at night).
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Not sure if you realize it yet, but you are dancing around an alternative to the V-block. If you have a good way to hold your rifle steady (e.g. Gun vise), place the scope in the rings but leave them loose enough that the scope can spin freely.
Hello improvised v-block.
Just take care not to scuff up the scope tube as you rotate. Line the inside of the rings with masking tape temporarily to prevent that from happening.
Now you can go in reverse and use a V-block to verify your results (just kidding...no reason to do that unless it just helps you sleep better at night).
I totally don't see any similarity? You may want to call a mounted scope ring a C block, V block it is not. The mounted scope rings are rigid and cannot move any way what so ever. Nothing rigid or permanent about V blocks. Can't use V blocks on my Airgun, I prefer scope alignment on my Air gun, not off somewhere on a table. :)
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What I mean is that either method serves as a fixture to optically center a scope.
You said to not be surprised if the scopes optical center changes when you put it into the scope rings. Why would it change? Optical center is a property of the scope; it has nothing to do with whether or how it is mounted. The only reason it may have some appearance of having changed is if the mount distorts the scope tube in some way.
There is no reason to do both and neither is inherently superior to the other.
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I don't see how you can rotate a scope in the rings all the way around to check the optical centering of the reticle anyway.... unless those are VERY tall rings.... All of my scopes the turrets would hit the receiver....
Bob
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Haha, good point Bob! That would have become apparent pretty quickly if one were to try it. When condor brought it up, it seemed logical that rotating the scope in the mount would yield the same results as a V-block. You know, except for the whole it's not possible thing ;D
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I found it interesting to read the instruction manuals for a couple scopes I have / had from different manufactures re: optically centering.
For example, Vortex recommends the "Count clicks & divide by 2" method for both their Crossfire II and Diamondback scopes.
Bushnell says to use the "Rotate the scope in a V block" method for both older and newer Trophy scopes while
instructions for an older RWS 450 never addressed the issue. I've used all three methods at different times on various
scopes and found that all of them got me close enough to optical center "for all practical purposes". You engineers should
recognize that last phrase. LOL!
As to the mirror method, I found that using it on a Vortex Diamondback gave me two different optical centers, both of which differed
from the count clicks method per Vortex. One Optical Center was obtained with the front plastic ring installed on the bell and a
different OC with the ring removed and the mirror against the metal bell housing. I essentially had three different optical centers,
all of which were within about 5 clicks of each other. It just goes to show that things are not truly square and accurately built.
On the other hand, a couple of Crossfire II's were centered with the count clicks method and checked with the mirror. It turned out that the
two methods were spot on in agreement. So you never know what you will get and it's nice to have alternative methods.
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I've used all three methods at different times on various
scopes and found that all of them got me close enough to optical center "for all practical purposes". You engineers should
recognize that last phrase. LOL!
Don't call Bob an engineer. He doesn't like that very much, haha! :D
Reminds me of a quote, paraphrased:
"Things should be done as well as possible...but no better."
I'm in agreement with you that good enough is, well, good enough. Bob was just trying to emphasize that even the tiniest bit of "unperpendicularity" between the scope tube and the objective bell translates into a surprising amount of error when using the mirror method. In manufacturing jargon, it's what's referred to as an uncontrolled parameter. The manufacturer has no particular reason to strive for the precision necessary to achieve this perpendicularity; it adds cost for a feature that >95% of the customer base will have no use for. And what I was trying to say is that in my opinion, there's just no good reason to leave it to chance when something as simple as a cardboard box or a wooden block can be used.
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What I mean is that either method serves as a fixture to optically center a scope.
You said to not be surprised if the scopes optical center changes when you put it into the scope rings. Why would it change? Optical center is a property of the scope; it has nothing to do with whether or how it is mounted. The only reason it may have some appearance of having changed is if the mount distorts the scope tube in some way.
There is no reason to do both and neither is inherently superior to the other.
I fail to see your logic, Optical center should be a property of better Accuracy, if it's not......then it's just a complete waste of time. ::) I see your point, it really doesn't matter where you align your scope, just makes better sense to me aligning it where I use it. ;)
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I don't see how you can rotate a scope in the rings all the way around to check the optical centering of the reticle anyway.... unless those are VERY tall rings.... All of my scopes the turrets would hit the receiver....
Bob
Why would it be necessary to rotate the scope 360 degrees? Did you miss where I stated "Don't let the turrets bang against the receiver". You could lay a rag under the scope, to keep from carelessly dinging the scope. ::)
Thanks for your response. I'll followup after talking to U.S.Optic's cs or ts.
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The more you can rotate the scope, the closer you can get to center.... You are correct that rotating the scope 90ish degrees in the rings can probably get you close enough, as shown in the video.... Realistically, close is all you need, as finding the "mechanical center" which is what all of the methods described in this thread do is not necessarily the perfect "optical center" anyway because the objective lense might not be mounted square to the tube and the bell itself could be off center relative to the tube.... neither are likely, but theoretically possible....
Bob
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The more you can rotate the scope, the closer you can get to center.... You are correct that rotating the scope 90ish degrees in the rings can probably get you close enough, as shown in the video.... Realistically, close is all you need, as finding the "mechanical center" which is what all of the methods described in this thread do is not necessarily the perfect "optical center" anyway because the objective lense might not be mounted square to the tube and the bell itself could be off center relative to the tube.... neither are likely, but theoretically possible....
Bob
+1 Thanks, it's just an accuracy thing*
Sam
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Just attempted to center my UTG SWAt 3-12 X44 and not getting to far...Using a grid printed on a piece of paper at 7 yards down the hallway and the AR15 in the caldwell with the top ring caps off (rings have some tape like material for traction on the inside).....did the mirror method first to get me close.......just did the elevation first and had to move the elevation down alot...put it back against the mirror for a look and it looks like the entire lens is up high in the tubes...does that sound right??
now with the windage it moves both to the left and to the right....how do I know which way I should turn the windage turret to adjust?
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Not sure, the center of the reticle, will make and arc off center. This arc is what you want to move toward the center, making the diameter of the arc smaller. Once centered the cross hair will spin like a propeller, instead of moving side to side. Hope this makes some sense?
You may want to zero the turrets at center on the mirror, and keep count of clicks used on the rifle.
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And then my greatest enemy scope CANT comes into question.... Always a problem for me... >:(
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best thread ever on that subject.... http://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0)
Bob
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I realized that when looking at it in the mirror that I was not getting a proper image which I am guessing was due to the large rubber cap cover on top of the sub shade on this scope...it most not lie perfectly flat against the mirror because the second time i whent to check it i noticed that as I moved it on the mirror the image would line up and the cross hairs would come into line.....guessing i have to make sure i am seeing a full field of view in the scope when using the mirror method with this scope and just get in the ball park with this scope.
yet, trying to spin it in the rings doesnt seem to be helping....after lining it up in the mirror it seems to be way off on the grid when i spin it...if i line up the elevation and then try the windage , moving the wndage in either direction doesnt seem to help....and then movint the windage seems to throw off the elevation again.
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When I first tried using the mirror I could see anything . Then a blurred image. Almost gave up in frustration. But other people do it,and the theory behind it seemed sound. So I was in another room and in that mirror I could clearly see 2 crosshairs,which I quickly made 1. The thickness of the mirror glass and lighting made the difference.
Realize that the most accurate method is the v-notch. But I found it to be a pain and not neede for my needs.
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When using the mirror to center your cross hairs turn your AO to the infinity mark and turn your magnification down to
it's lowest setting for starters. Good lighting, as mentioned above, is also necessary. Make sure you position your head so
that you are at the correct distance from the scope and you are getting a full image. If you see a dark ring around the
edges of the inside of your scope, you are either too far or too close from / to the scope. Move your head around - head bop.
HTH
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Having enough light is VERY important for the mirror method. Pressing the Objective lens ring against the mirror makes the image very dark and hard to see the crosshairs.
I have a large hand held mirror that I use for this. I usually lay the mirror down on my back deck so as to catch as much sunlight as possible. Just remember, DO NOT look at the sun's reflection in the mirror through your scope. I can't say that enough. DO NOT LOOK AT THE SUN OR IT'S REFLECTION IN THE SCOPE!!!
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I'm sure that most of you (including me) that have tried using V-blocks to optically center a scope have found it a frustrating experience, fiddling with the turrents and seemingly making things worse instead of better.... Here is a simple diagram I made up to explain what is happening and hopefully a method to help you both understand what is happening, and use that knowledge to make the job a lot easier....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/OpticalCentering_zpsd449400c.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/OpticalCentering_zpsd449400c.jpg.html)
The first revelation is that you don't WANT to rotate the scope 360*, in fact you want to rotate it exactly 180* during this operation, 90* to the left and 90* to the right (diagram is your view through the scope).... The reason for doing it this way is to be able to separate the two adjustments in your brain.... Most commonly you will see something like the right hand drawing.... In this example, when you rotate the scope CW 90*, the reticle ends up at about 4-o'clock (ie both low and right) and at 90* CCW it ends up at about 10 o'clock (high and left).... This error can be separated into the windage and elevation error, as shown in the other two diagrams.... If the windage is centered and there is only an elevation error, you will have the situation in the left drawing.... The end points are at 9 o'clock and 3 o'clock, in other words they are separated left and right, but at the same height.... If the elevation is centered and there is a windage error (middle drawing), the end points are at 12 o'clock and 6 o'clock, they line up horizontally, but at different heights....
How can you use this starting from the right hand drawing?.... You have already determined that both the height and width of the end points are moving.... Viewing a piece of graph paper as your target will help you with rotating the scope exactly 90* either way....
1. Adjust the elevation so that the arc gets smaller, until the end points, when the scope is rotated 90* CW and CCW, are directly above one another (like the middle drawing)....
2. Then adjust the windage so that the arc gets smaller and eventually disappears....
Repeat steps 1 and 2 if necessary.... When you get the reticle centered in the tube, the aiming point of the reticle won't describe a circle, it will stay still and the crosshairs will just rotate around it like a propeller.... Your reticle is then centered in the tube....
Bob
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best thread ever on that subject.... http://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0)
Bob
An excellent thread Bob, made specially for guys like me with the cant enemy... LOL ;D
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Thanks for the cheat sheet. One question: the little black "x"s are the center of the scope or a target spot?
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Maybe if I had this understanding from the beginning I wouldn't have been so against it . You make it so much easier to understand. I would do it with my circle going all over the place and end with a " this is stupid " comment [to myself cuz I'm crazy]. Thanks
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Thanks for the cheat sheet. One question: the little black "x"s are the center of the scope or a target spot?
Scope's center.
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The first revelation is that you don't WANT to rotate the scope 360*, in fact you want to rotate it exactly 180* during this operation...
...The reason for doing it this way is to be able to separate the two adjustments in your brain.
Very well said as usual, Bob.
That was the key for me also. The first time I tried to use a V-block it took me a few minutes to get the hang of what I really needed to do. I needed to divide and conquer...break it into smaller steps that I could comprehend. It was then I realized I could separate the X and Y axes:
[The goal of centering is to] have the intersection of the crosshairs remain in the same place throughout the rotation. The way you do that is focus on one turret at a time. Doesn't matter which one you start with so I'll pick the windage. Orient the scope normally and take note where on the X-axis of your target the crosshairs rest. Then rotate the scope 180° and take note again where the crosshairs end up on the X-axis relative to the previous spot. Now adjust the windage turret to an imagined midway point between those two spots.
Repeat this back and forth until the spot on the X-axis ends up in the same place when you rotate the scope 180°. While you are rotating the scope back and forth, you will probably notice the crosshairs orbiting against your target. You want to ignore that. All you care about right now is the X-axis and where the crosshairs end up left-to-right when the scope is oriented normally versus when it's upside down (rotated 180°). What it does in between those two points is of no interest.
Once you have the windage fine tuned, now turn your attention to the elevation turret. Same idea except you're now focusing on the Y-axis.
When you're done, you should be able to rotate the scope 360° and the crosshairs will remain in the same spot on the paper.
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The little black x's are just the center of the tube, so they are the point the scope is rotating around....
nervoustrigger, our methods are the same except you are going 180* from "normal" and I was going 90* each way.... Your explanation (which predates mine) is perfectly correct.... Yours is actually easier to understand because a vertical change requires an elevation adjustment and a horizontal change requires a windage adjustment....
Bob
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I'm sure that most of you (including me) that have tried using V-blocks to optically center a scope have found it a frustrating experience, fiddling with the turrents and seemingly making things worse instead of better.... Here is a simple diagram I made up to explain what is happening and hopefully a method to help you both understand what is happening, and use that knowledge to make the job a lot easier....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/OpticalCentering_zpsd449400c.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/OpticalCentering_zpsd449400c.jpg.html)
The first revelation is that you don't WANT to rotate the scope 360*, in fact you want to rotate it exactly 180* during this operation, 90* to the left and 90* to the right (diagram is your view through the scope).... The reason for doing it this way is to be able to separate the two adjustments in your brain.... Most commonly you will see something like the right hand drawing.... In this example, when you rotate the scope CW 90*, the reticle ends up at about 4-o'clock (ie both low and right) and at 90* CCW it ends up at about 10 o'clock (high and left).... This error can be separated into the windage and elevation error, as shown in the other two diagrams.... If the windage is centered and there is only an elevation error, you will have the situation in the left drawing.... The end points are at 9 o'clock and 3 o'clock, in other words they are separated left and right, but at the same height.... If the elevation is centered and there is a windage error (middle drawing), the end points are at 12 o'clock and 6 o'clock, they line up horizontally, but at different heights....
How can you use this starting from the right hand drawing?.... You have already determined that both the height and width of the end points are moving.... Viewing a piece of graph paper as your target will help you with rotating the scope exactly 90* either way....
1. Adjust the elevation so that the arc gets smaller, until the end points, when the scope is rotated 90* CW and CCW, are directly above one another (like the middle drawing)....
2. Then adjust the windage so that the arc gets smaller and eventually disappears....
Repeat steps 1 and 2 if necessary.... When you get the reticle centered in the tube, the aiming point of the reticle won't describe a circle, it will stay still and the crosshairs will just rotate around it like a propeller.... Your reticle is then centered in the tube....
Bob
does the direction of the arch dictate which direction you need to move the reticle...I have the arc going in the opposite of the first picture, which appears to show the reticle is too high...would that mean my reticle is too low and would need to be raised since my arc is reversed (points on the top)
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In theory that would be correct, but the image of the target is inverted at the reticle location.... and then that combined image is inverted again by the eyepiece lense.... Try it and let us know, will you?.... *LOL*....
Bob
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In theory that would be correct, but the image of the target is inverted at the reticle location.... and then that combined image is inverted again by the eyepiece lense.... In addition, to raise the muzzle, you need to lower the line of sight.... Try it and let us know, will you?.... *LOL*....
Bob