Scope Question

[bboswell]

Dustoffer's post is correct. The AO or "side focus" if you have that instead of AO, is to adjust for parallax in the scope. As you change magnification the mirrors move inside the scope and can misalign and cause your POI to shift, but in reality it doesn't you just have to dial everything back in alignment. Like he mentioned if you have your AO set for 200 but are shooting at 100, if you move your head, the crosshairs will appear to move as well. The reason you believe your other scopes move when going to higher power magnifications is because if you don't have AO or SF, then most scopes are set at a fixed parallax adjustment for 100 yards. Anything closer or farther than that will introduce parallax and if your head is not in the exact same position each time, it will cause you to be off target. This usually comes more into play at higher magnification and with lesser quality scopes.

Anything over 9-10x magnification is a must to have AO or SF IMO.

Thoroughly confused yet?

I could go into why Mil Dot and BDC scopes are only accurate at a certain magnification range but that opens a whole nother can of worms regarding first focal plane and second focal plane.

So much better than I could of said it and exactly why I didn't try.

[Cuz]

So much better than I could of said it and exactly why I didn't try.

Don't let his looks confuse you, Mikes a purdy fart smeller!

[TexZ71]

It should not affect anything to do with impact, that's the turrets job. The AO is for clarification.

X2

[Cuz]

X2

You should have read past post #3...

[TexZ71]

You should have read past post #3...

I did, what is your point?

[Bonesplitter]

I guess I should have went into greater detail concerning the parallax adjustment. Imo proper cheekweld is just as or more important. Getting into ffp and sfp can get confusing so I wont get into that either.I was giving a quick answer to a fairly simple question regarding an adjustable objective. Adjusting parallax is basically focusing the reticle on the same plane as the target so the crosshairs do not appear to move causing a slight change in point of impact, hence the clarity terminology.

[TexZ71]

I guess I should have went into greater detail concerning the parallax adjustment. Imo proper cheekweld is just as or more important. Getting into ffp and sfp can get confusing so I wont get into that either.I was giving a quick answer to a fairly simple question regarding an adjustable objective. Adjusting parallax is basically focusing the reticle on the same plane as the target so the crosshairs do not appear to move causing a slight change in point of impact, hence the clarity terminology.

Bingo.

Thanks

[dadogg]

It should not affect anything to do with impact, that's the turrets job. The AO is for clarification.

this

[texag93]

I know the answer and now my head hurts.

[denowt]

Talking about a Burris FullField...


I know it's for focus but I also know that when you adjust power on a scope it messes with the poi. For example, with my Nikon/my wife's bushnell/my dads leupold, when you shoot at 100 yards on 5 power and you're dead on then move to 9 power and shoot again at the same range you're a few inches high, or low can't remember which it is. Even if you look at Nikons ballistic chart for their BDC reticles its shows that at X yards on X power it's on. Confirming that adjusting the power DOES effect poi/crosshair center.
So I was wondering if adjusting the AO did the same. Like focusing the crosshairs moves them a bit too...

The Nikon ballistic chart you refer to is for the hold-over marks. Your main crosshairs should not change POI when changing magnification. If it does, it's because of parallax as others have already mentioned, because your eye/head is not in the exact same position OR you have a bad scope. If you have the same results on several different scopes, I would say it's the shooter.

My current Nikon (4-12x40 not mildot) does. At 8x its dead center at 100 yards but on 12x its off (again, I can't remember if its high or low).

Also, how can the "holdovers" on a mildot be set for a certain power but the crosshairs aren't? They're all "fixed" in the scope right?
I'm NOT agruing here, just trying to learn and understand before buying an AO scope. Thanks

The holdovers don't change their position, but the distance between them on the target at different powers will change.
Example, at 100 yards and 3 power, the distance on the target between the main crosshairs and the first holdover mark will be 4".
Move it to 9 power, and the distance between them will be 12".
If you are using the main crosshairs, your POI should be the same with both powers.
But if you're using the first holdover mark, your POI will be 8" difference.
These numbers are not real numbers, I just made them up for simplicity, but you get the idea.
Easy way to see for yourself, is set up a yardstick vertically at 100yards with 0" at top and 36" at bottom. Put your scope on low power and aim main crosshairs on the top of yardstick. Without moving scope, look at where the holdover mark is at. Then move scope up to high power and repeat. The holdover mark will be in a different spot on yardstick.

Mildot or crosshair holdovers are fixed. But they may be set for 100, 200, 300, 400 at a set power of magnification. Trust me, it gets confusing and complicated but changing in magnification changes what the holdovers are zeroed at. The MAIN crosshair should not change but remain zeroed at 100 regardless of magnification.

This is what you will see if you do the yardstick thing I explained above.

ddavis hit it head on....

lets take the zeiss for example, with the rapid z reticle as i just went through this, and if why i chose to turn turrets instead of holdovers on a reticle (turrets are so much easier)

your center is always gonna be your center, it should not move ever, it would be shooter error with that happening or your scope is broke!!

lets say your second mark in the scope is for 300 yards, and at 14 power the distance between center and the 300 yard mark is 4 inches.... so you zoom out to 8 power and now its a difference of 8 inches(just an example) so you doubled the distance in between thus moving the holdover, causing the shot to hit a lot higher than it would at 14 power....

disclaimer!! this is how i understand it, im no pro.... but i do think it is correct info, and someone will correct me if im wrong, especially on this forum lol

This how I understand it also.

#1) Oh man, now my head hurts! lol. Not understanding WHY the mildots would change and the main crosshiar doesn't when adjusting power?? The mildots or rings on a bdc ARE fixed and on the crosshair right?

#2) Dustoffer, I believe you are correct. I think the AO is for crosshair clarity and stability at all yardages...

Main crosshair is in the center and should not change POI with different magnification settings, unless parallax problems are moving the crosshairs. Even then, the crosshairs are not actually changing POI. It's the way it appears because head/eye is not perfectly aligned with scope.

I'm sorry Sir but it does. Out of AT LEAST two different Nikons (prostaff & monarch), 2 different Leupolds (rifleman & varix iii) and one Bushnell (Elite) that I have shot. Moving the power up/down does effect the center of the crosshairs. I know it's not me/the shooter because I'm using a deadsled and basically line it up and squeeze off. No way for me as the shooter to be messing it up. Regardless of the power setting.

I have Leupolds on all my rifles, from rifleman to V-IIIs. POI does not change on any of them when I change magnification on the main crosshairs. On the scopes with holdover marks, yes they change, but not the main crosshairs.
Cheaper scopes and high power induce parallax problems which make the crosshairs APPEAR to move on target if your head/eye is not exactly the same every time.

Clear as mud yet?

[Cuz]

Good stuff Den. Thanks!

[ducks-and-bucks]

Mike D has my vote!!!