focus and parallax


PDA






kkayser
December 14, 2013, 10:00 AM
On the Nikon Monarch and the Sightron SIII scopes, parallax and focus are the same knob. What happens if best focus and zero parallax are not at the same position of the one knob? Do you get to choose one or the other?

If you enjoyed reading about "focus and parallax" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
Walkalong
December 14, 2013, 10:40 AM
The parallax adjustment is not a focus. It is fro removing parallax. The eyepiece is adjusted to put the focus on the same plane as the image.

HOOfan_1
December 14, 2013, 11:20 AM
Actually according to Nikon it is both...and when you have it focused best on the target, you have adjusted for parallax

https://support.nikonusa.com/app/answers/detail/a_id/17295

Corn-Picker
December 14, 2013, 12:18 PM
My bushnell elite 6500 2.5-16x42 is supposedly the same way -- parallax and focus on the same side knob. I say supposedly because the reticle still moves around a good bit when the focus/parallax is set to 100 yards and I'm shooting at 100 yards. When I'm in your situation I usually turn the magnification down until the image focuses, but I'm not trying for the world's tiniest groups , so I don't need max magnifacation at 100 yards.

wally
December 14, 2013, 12:40 PM
Actually according to Nikon it is both...and when you have it focused best on the target, you have adjusted for parallax


My bushnell elite 6500 2.5-16x42 is supposedly the same way -- parallax and focus on the same side knob. I say supposedly because the reticle still moves around a good bit when the focus/parallax is set to 100 yards and I'm shooting at 100 yards.

I suspect some advertising copy writer was confused or messed up the language translation.

I don't believe this is optically possible with a "normal" second focal plane reticle. The objective focuses the image into the plane where the reticle is and the eyepiece focuses this plane to where your eye can see it clearly. The objective can only focus a single object plane into the plane of the reticle which is the distance at which the scope is "parallax free". Although they could trade clarity for parallex free by making the object plane at infinity.

Laphroaig
December 14, 2013, 12:46 PM
I've always wondered about this topic.

I own 3 AO scopes, two of which are of the less expensive category. All three don't always bring the sharpest focus at the yardage mark on the dial. I've assumed that the marks were out of calibration, which seems to be the case based on #3.

Thanks for clarifying this!

Laphroaig

wally
December 14, 2013, 12:55 PM
With an adjustable objective (front or side or whatever focus) you first set eh dial to "infinity" and then focus the eyepiece by looking at clear, featureless sky. Then when the objective is focused you will be parallax free at that distance. The relationship between the numbers on the dial and actual distance will be a strong function of price.

Gohon
December 14, 2013, 09:25 PM
My understanding is the scopes are set at the factory for 20/20 vision to bring the cross hairs into focus. The focus whether fast focus or lock ring type on the eye focus, does nothing more than to allow one to put the cross hairs into focus for their eyesight. Has nothing to do with parallax or objective focus to my knowledge.

Outlaw Man
December 14, 2013, 11:57 PM
Walkalong is correct. If I'm reading Wally's first post correctly, and I think I am, he's explaining it. When the parallax is set properly, everything is in "focus." That shouldn't be your judge of parallax error, though.

The parallax adjustment (if that's truly what it is) is moving the reticle back and forth to line it up with the focal plane. If your eye changes position, the reticle will "move" if this isn't set correctly.

Trent
December 15, 2013, 02:32 AM
If you pay very close attention you can feel your eye focusing on the target and the reticle differently if parallax isn't set right..

Parallax adjustment (for TRUE parallax adjustment) must happen at the reticle plane, not at the objective end or eye focus plane.

Focusing the target and setting parallax are two entirely different functions happening at different points on the scope.

If you don't have three turrets in the middle (parallax, elevation, and windage), your scope doesn't really have true parallax adjustment.

It only has focus adjustment (which helps SOME with parallax but not 100%).

Which means your eye must be perfectly centered when you move from one range to another.

Nightforce NXS with zero stop parallax on the reticle plane.

http://i.imgur.com/fWVZImqh.jpg

Expensive Bushnell laser rangefinding scope with focus adjustment, but no true parallax adjustment:

http://i.imgur.com/ccKPX7oh.jpg?1

I had that Bushnell mounted on an FNAR wheen I got the surprise of a lifetime and dropped 20 points on a match, by hitting my group 8" low when I transitioned from bench zeroing, to prone @ 200 yards.

Shot fine on the bench.

Shoots 8" low prone.

(Until I corrected my cheek weld.)

Target was perfectly in focus but since the scope has no "true" parallax adjustment....

Norrick
December 15, 2013, 04:07 AM
side focus is often used interchangeably as a descriptive term for parallax adjustment on a scope with a third turret (when normally parallax adjustment would be via the adjustable objective) it serves the same function but is adjusted differently.

the eye piece focus is for focusing the reticle, the second focus (parallax adjustment) is for focusing the target. Ideally, both are in focus at the same time and there is no parallax.

In practice you know this isn't always the case as a fixed parallax scope can have its crosshairs focused against the background image of your target and there is noticeable parallax.

my method is:

- look at the sky through the scope, but not directly at the crosshair

- fixate on that little patch of blue sky and using your peripheral vision, focus the crosshairs using the eyepiece adjustment. Try to relax your eyes if you know how. Not everyone can do this. But for me when I used to go to class, I would daydream and stare into the distance and everything would go blurry. Thats the feeling you want in your eyes when focusing the reticle. I can do this now on command and its very helpful for this process.

- now whatever you look at, use the adjustable objective or side focus (whichever yours has) and focus the target image to match your reticles focus.


if you do this correctly, you should have no problem looking through the scope for longer periods of time and parallax should be minimal. Don't worry about the graduations being calibrated so much, they're more for show than anything. On some scopes where the adjustable objective can go close to 360 degrees its useful to get to a ballpark area.

kkayser
December 15, 2013, 11:54 AM
Thanks to everyone.

From all of this, I think that makers build scopes so that zero parallax and target sharpest focus are the same for 20/20 vision. Of the two, parallax would seem to be more important. If the bull is a little blurred, one can still center the cross hairs, and the hit point and aim point will be the same. However, if there is parallax error, the hit point and aim point will be different.

Ideally, there should be three knobs: reticle focus, target focus, and parallax adjustment. Does anyone know if such a scope exists?

Lacking 3 knobs, it would seem that one would have to try different scopes to see which is best for your aiming eye.

Walkalong
December 15, 2013, 04:54 PM
I shot some groups today at the range with a scope I haven't used in a while. Adjusting the parallax with the front objective the target was clearest at the 75 yard mark, but there was parallax present. The parallax was gone at the 100 yard mark, but the target wasn't quite as clear. After playing with the eye piece a little, the image was clear and the parallax was gone. Win win.

The wind was terrible (Gusting and switching), and good groups were difficult to come by, but I had a good time and gathered some some info on the loads.

I usually run a Nikon 3X scope on my 300 BLK, but slid the Simmons 6.5X20 on to test for accuracy. Funny thing is after that I put the 3X back on and shot one of the best groups of the day. Go figure. :)

If you use the parallax adjustment to just clear up the image, you may not be eliminating parallax. You have to have the gun in a rest it where it can sit completely stationary and move your eye back and forth behind to see if the parallax is is gone or not.

Do not stare through the scope too long when checking adjustments for clarity, as your eye will adjust and fib to you.

Lloyd Smale
December 15, 2013, 07:15 PM
you can call it what you want but i sure know that if im looking at a deer at 500 yards with my paralex set at 50 its sure out of focus.

Walkalong
December 15, 2013, 08:35 PM
While that is absolutely true, it doesn't make it a focus knob. Yes, it does affect focus, and can certainly make the sight picture completely blurry if it is way off. :)

Corn-Picker
December 16, 2013, 09:20 AM
So what is the relationship, if any, between parallax adjustment and magnification? If I adjust the side focus to be parallax free at 100 yards at 8x magnification, will I also be parallax free if I turn it up to 16x or dial it back to 2.5x?

I know that my groups at 100 yards are bad (2-3" or more) with my fancy 2.5-16x scope, but better (1-1.5") with a less expensive 1-4x scope (no parallax adjustment available). This is despite the fact that at 4x at 100 yards my reticle lines cover a two inch diameter bullseye sticker.

So I need to figure out what the problem is with my 2.5-16x setup. It's either the scope, mounts, or the loose nut behind the trigger (that's me). My first step is to mount the 2.5-16x scope on my current deer rifle. I know that rifle/base/ring setup produces good groups with my 1.25-4x scope. I want to be confident that I know how to use my 2.5-16x scope to it's fullest before I conclude that it's broken and send it back for repair.

I will say unequivocally that Bushnell needs to do a better job with documentation. The user manual that came with my Elite 6500 2.5-16x42 is exactly the same (and just as bad) as the user manual that came with my Elite 3200 1.25-4x24 illuminated scope.

Walkalong
December 16, 2013, 09:31 AM
If I adjust the side focus to be parallax free at 100 yards at 8x magnification, will I also be parallax free if I turn it up to 16x or dial it back to 2.5x?Should be. The parallax setting is for distance.

I see absolutely no need for a parallax adjustment on a scope for hunting, unless you might be taking a shot from up close to very far away, and 99% of folks are not hunting in such a situation. Besides, parallax is also eliminated by having your eye centered.

Parallax adjustment is only needed for target work in my opinion. The error is tiny if your eye is anywhere close to centered.

I do like to put a higher power scope, possibly with a parallax adjustment on it, to test a load on the AR, but only because it is so easy to switch them out. As posted earlier. I shot one of my best groups with the 3X scope. Three touching each other and two hanging out, one of which was real close.

wally
December 16, 2013, 09:35 AM
If I adjust the side focus to be parallax free at 100 yards at 8x magnification, will I also be parallax free if I turn it up to 16x or dial it back to 2.5x?

If the optical tracking of the "zoom" is correct it should be, but its one of the areas inexpensive scopes sometimes fall down on.

I know that my groups at 100 yards are bad (2-3" or more) with my fancy 2.5-16x scope, but better (1-1.5") with a less expensive 1-4x scope (no parallax adjustment available)
I suspect the extra magnification makes your "wobble" (from heartbeat, breathing, etc.) much more noticeable and you are not "timing" the shot properly. When everything looks stable, you are more relaxed and time the shot more consistently resulting in tighter groups.

Upon further review, if you are talking about two different scopes and rifles, all bets are off -- could be shooter, trigger, rifle/ammo combination, mounts, or scope problem. Expensive doesn't completely eliminate the possibility of a defective unit.


Oftentimes a cheap scope is effectively parallax-free because the small exit pupil forces your eye to be essentially centered to see the full circle.

Corn-Picker
December 16, 2013, 10:14 AM
Wally, it's the same rifle/ammo, but different base/rings/scope.

Previous setup (large groups):
Weatherby Vanguard S2 youth in 308
Federal match king
Bushnell Elite 6500 2.5-16x42
Warne steel bases
Burris signature zee rings

New setup (significantly smaller groups)
Weatherby Vanguard S2 youth in 308
Federal match king
Bushnell Elite 3200 1.25-4x24
Talley lightweight one piece base/rings

I'm shooting from a bench and I am capable of shooting groups small enough to know that something (other than me) is wrong with the first setup. The inaccuracy of the first setup was confirmed with eight types of ammo over multiple range trips (with multiple shooters). At this point I'm convinced it's the scope or base/rings. By switching the 2.5-16 scope from my problem setup into the new one-piece base/rings I should be able to determine if it was the base/rings or scope that was the problem. I agree that parallax is probably not the issue, when I purposely moved my eye to the extreme edges of the 2.5-16x scope the reticle didn't move more than an inch total. My groups with the 2.5-16x scope were twice as big than they were with the 1.25-4x.

Jim Watson
December 16, 2013, 10:20 AM
I think the adjustable objective is optically superior for minimizing parallax, although the side knob is more convenient.
Apparently you can't do only one thing when you start shifting lenses around. My Leupold with side knob does not give clearest focus at the least parallax. I will tinker with the eyepiece as Walkalong describes.
Which brings up another item. I prefer the binocular type "fast focus" ocular adjustment to the old system of winding the eyepiece in and out on fine body threads. Your eye gets tired before the focus is clear.

Walkalong
December 16, 2013, 11:39 AM
I agree. The side objective adjustment seems to be courser and harder to adjust, but is definitely convenient if you do not want to re-adjust your shooting position. For plain old target shooting the front objective is my preference. I can live with either one though.

If you enjoyed reading about "focus and parallax" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!