parallax question

sniperman

hi folks,thinking of getting a 6-24x50 hawke scope,i know what parallax is,(least i think i do) the question,am i right in saying if im on 24 mag punching paper,and i side focus till target is clear,is that the parallex set for that distance?

One shot on kill

I'm not up on parralax myself but that's what I'd do I'd set my scope on which ever power I want and adjust parralax till its good. I'd just leave things the way they are then.

wildcatares22

if you eye up your target and then while moving your eye side to side or up/down, and the crosshair remains on your target spot, then your parallax is set. you can have your parallax correct and still have a blurry picture because the focus is off.

One shot on kill

I was actually just told that the other day to be fair.

But my question to that would that not be because of the shape of the ocular lense

extremetaz

sniperman wrote: »

hi folks,thinking of getting a 6-24x50 hawke scope,i know what parallax is,(least i think i do) the question,am i right in saying if im on 24 mag punching paper,and i side focus till target is clear,is that the parallex set for that distance?

if you're at short range (<100m) and high mag (>20) then the above method will easily get your parrallax correct to within about half a meter, which is as good as you'll ever need it to be.

At longer ranges, you can't rely on the focus alone though as the depth of field increases dramatically, meaning that you can be perfectly focused but parallaxed well away from your target plane. So once you're out beyond about 100m I'd be inclined to use the PoI shift check that wildcatares mentions if you're really determined to be spot on with it.

Incorrect parrallax can make quite a difference when you're punching paper, but only if your head placement varies between shots - which it shouldn't - so if you're noticing parrallax effects on paper then it's more of a symptom of what's wrong, than the actual problem itself.

As for field applications where parrallax is critical - I can't think of anything you'd be shooting in Ireland that would require you to worry too much about it unless you're trying to hit bunnies from 300+.

One shot on kill

When moving your eye are you talking about when the gun is clamped or just very small movements. When looking trough the scope or should the rifle be completely steady like in a clamp of that.

When you say parralax is right and the focus is off is that just your eye piece. Adjustment.

Cass

One shot on kill wrote: »

When moving your eye are you talking about when the gun is clamped or just very small movements. When looking trough the scope or should the rifle be completely steady like in a clamp of that.

This might sound odd so bear with me.

Have it clamped. Aim your rifle at a target. Purposely put it slightly off target. If you look through the scope, and you can place the crosshairs on the target simply by moving your head/eye, but without touching or moving the rifle then the parallax is off.

When you say parallax is right and the focus is off is that just your eye piece. Adjustment.

The eyepiece or ocular adjustment. It's like a fine tuning. It sharpens the crosshair. Use it in conjunction with the parallax adjustment.

One shot on kill

I was under the impression that the ocular lense should be adjust till the cross hairs are nice and crisp while not actually focusing on anything trough the scope.

Cass

It should. My bad. How a simple wrong choice of word can mean so much.

The ocular focus is for the crosshair, and the parallax for the image/target.

One shot on kill

We're all human thanks all the same.

extremetaz

One shot on kill wrote: »

When moving your eye are you talking about when the gun is clamped or just very small movements. When looking trough the scope or should the rifle be completely steady like in a clamp of that.

..see Cass' response - when parrallax is set correctly, you shouldn't be able to shift the reticle with respect to the target simply by moving your head.

One shot on kill wrote: »

When you say parralax is right and the focus is off is that just your eye piece. Adjustment.

..I certainly didn't mean to say this... for what it's worth though, in theory that's correct, it would be a back focus (occular focus) adjustment which is required - however, both your target and your reticle would be out of focus so I'm not sure how this situation would ever arise.

As mentioned earlier, the occular focus ring allows you to set the back focus for the entire lense that is the scope. With the back focus set correctly then the principle is that for a given range, the focus should not shift regardless of magnification - so in simple terms, setting the back focus to compliment the reticle means that even if you vary the magnification, the reticle will always stay sharp.

We then use the front lense to bring the target focal plane into the reticle focal plane - when the two are lined up perfectly, the reticle is effectively in the same plane as the target so it will not move wrt the target.

However - the depth of field (depth of the region of sharp focus for the front lense) is a function of the range to target and the fixed focal length of the front lense (which is to do with the shape of the lense and cannot be varied).

As the range extends, so too does the depth of field - at 20 meters the DoF might be 30cm, at 50 meters, it could be 90cm, at 100m it may be 2m and will continue to increase exponentially as your target distance increases.

This means that having sharp focus does not guarantee that you are correctly parrallaxed (that your reticle and target focal planes are actually set equal) - hence any variation in head placement may result in a shift in PoI.