PARALLAX Etc...

[joliver]

Okay - changed the heading of my post to be a bit more precise there:-)

I'll use this post to do several things at once: introduce myself as a new member and THEN ask for some help with a problem that is driving me nuts, etc.

First of all - John is the name and I'm in Perth - EXTREMELY new to F Class Standard - shooting with a local club for the last month or so - haven't shot long arms for about 20 years - only got back into shooting in the last 3 years or so - but mostly handgun shooting...

Long range rifle shooting has *changed* in the 20 years plus since the last time I had a go - I feel like a TOTAL babe in the woods here:-(

I'm going to stick with F Class Standard for the moment - I don't have a 'race gun' as such - here is what I am shooting:

Rifle: 7.62 NATO Remington 700p TWS with 26" barrel (1 in 12 twist)
Scope: Nightforce NXS 5.5-22x56mm with mildot reticle...

I don't 'roll my own' in terms of ammo - I shoot what the club sells/I am allowed to shoot in Standard - the 155gr Winchester Palma Match...

I use the Harris Bipod which came with my gun and since the original Leupold Scope (Vari X III 3.5-10x40mm) which came with the gun was DOA (have spent 80 bucks to send it straight back to Leupold in the US for repair or replacement) I decided to 'bite the bullet' and spend the cash straight off to buy a really good scope (which is why I went for the Nightforce).

NOW: the QUESTION PART of this 'Swiss Army Email':-)

HOW DO I CONFIRM/DISCONFIRM that I have a SERIOUS PARALLAX PROBLEM?????

One of the top shooters in my club has told me that my scope has "about 1.5 moa of parallax" - and I have to admit I think I noticed some problems/movement when I moved my head around a fair bit at the range last week (shooting 300/500/600 yards) and with the scope cranked up fully to 22x...

HOWEVER - on Saturday I shot at 400 yards and the only real problem I was having was the fairly horrendous/unpredictable winds my range gets (I'm learning to read windage all over again:-)))

My Leupold Scope is going to be away in the US for a while getting sorted - my NIGHTFORCE Scope I either have to send off to the agent in Adelaide (and they will send off to the US and get it fixed for me) so NOW what I need to know is THIS:

Q. HOW do I confirm there is/isn't a problem ASAP because if there is the agent in Adelaide has said he'll send me a temporary replacement of the same type while mine is getting sorted - but I DON'T want to waste everybody's time (and look like a complete idiot) getting something fixed that ain't broke:-)

OKAY - my apologies for the long post - HOPE someone on this board can help me out here...

Many thanks in advance,

John in Perth.

[Simon C]

Firstly, welcome to the sport.

With regard to parallax adjustment, u need to look thru the scope whilst adjusting the parallax knob. Adjust it until the image is clear then move your head ever so slightly up and down. If the X-hairs move, continue to adjust the knob until they remain stationary. When they are stationary, your parallax adjustment is correct.

THe other issue is the presence of scope shadow in your sight picture. This is related to your head position and will seriously affect shot to shot consistency. U cannot have any shadow whatsoever. Position your head until there is a nice clear and crisp ringed image.

Shoot with both the parallax correctly adjusted and eliminate the shadow and see how u go. If there is still a problem, I would be looking at action screw tension (65 in/lbs for your remington is a good start) and ring/mount tensions.

I would seriously doubt there is a problem with your NXS....If there is, call them and ask for a replacement whilst yours is getting sorted.

[joliver]

Many thanks for that Simon - much appreciated.

I'll get to the range early on Saturday and spend some time doing exactly what you've suggested...

I guess what has me wondering is the fact that I'm basically shooting okay at the moment and I seemed to have a very good sight picture when I was shooting at 400 yards on Saturday - its only my fourth or fifth shoot (long range rifle shooting) in 20 years plus and I ended up coming third on the day - and I'd guess that if there was a real/serious problem with the scope it SHOULD (?) have impacted on my shooting quite significantly/I should have done a lot worse (?)

Anyway - I've told the Nightforce guy in Adelaide that I'm going to hold off sending him the scope until after I've had another look at it/tested it out again in the 1000 yard shoot this Saturday - and if that all works out/I get the right sight picture and manage to eliminate any apparent problems then there's no point sending it off anymore...

John.

[AlanF]

John,

Just to add to Simon's advice, your Leupold and NF will have 3 things to adjust : (1) Cross-hair focus (2) Object focus (parallax adjustment) and (3) magnification. I would suggest setting maximum magnification, and doing the testing both at the shortest and longest ranges you shoot (e.g. 300 and 1000yds) in good sighting conditions (i.e. no mirage).

Firstly, adjust the cross-hair focus (against the sky or other non-detailed background). Then adjust the object focus on the target. You should now see both cross-hair and target as sharp images - if not adjust both again. Then position the rifle pointing at the target on a steady rest, look through the scope and move your eye position around a little, being careful not to move the rifle. If the cross-hair moves against the background, adjust the focus slightly and try again. Keep doing this until by trial and error you have a focus setting where there is no movement between cross-hair and target. You have now elimated the parallax. But what if the target is now out of focus, and not as clear as it could be? Answer - the scope needs adjusting at the factory.

I hope you find the're both okay!

Alan

[Lynn Otto]

One of the top shooters in my club has told me that my scope has "about 1.5 moa of parallax"

John, both Alan and Simon have given you some very sound advice.

My comment to the above quote is that everyones eyes are different, so the parallax this gentleman may have been seeing, may not be there for your eyes with the current scope settings. That is, every scope needs to be set for the person using it. I can not use my husbands scope, lol, I'm not sure what version of eyesight he's using, nor can I use my son's scope, who has the sharp eyesight of an eagle. While you may get away with using someone else's scope at a pinch it is best to set your scope to what is best for you and your eyesight.

Welcome and good shooting
Lynn

[Simon C]

I guess what has me wondering is the fact that I'm basically shooting okay at the moment and I seemed to have a very good sight picture when I was shooting at 400 yards on Saturday - its only my fourth or fifth shoot (long range rifle shooting) in 20 years plus and I ended up coming third on the day - and I'd guess that if there was a real/serious problem with the scope it SHOULD (?) have impacted on my shooting quite significantly/I should have done a lot worse (?)

The result on the target face would depend on how accurately your parallax was set in the first place. You may have had it almost right hence the decent result....so u COULD have done a lot worse...but also better if the scope was set up better

If u got vertical dispersion, I would say that it was due to the parallax. Keep going with the harris bipod. I love them and shoot them on both my F-Class rifles with good results....I'm sure there will be differing opinions

[pjifl]

This is mainly a repeat of what others have said but with a few slight differences. Hope it helps.

1/ ALL quality scopes which can be focused for different ranges have parallax if not fosused properly by the shooter for the range at thich it will be used. It does not have to be adjusted by the factory - in fact it cannot because the scope will be used at different ranges. Cheap low power hunting scopes may need adjustment by the factory but that is not what we are talking about here. And these low powered hunting scopes have a compromise setting and are wrong for other ranges.

2/ The parallax adjustment needs to be repeated for different ranges for perfection. Different enough from 300 to 800 to notice it. But when moving from 1000 to 900 to 800 you will not pick the difference. So in practice adjust when moving ranges from or to 300, 500, The longer ones are more or less the same.

3/ Parallax is adjusted only by the objective (on some the side) focus. It stays the same whoever uses the scope. So once focused for a range distance anyone can refocus the eyepiece focus for themselves without changing parallax. The eyepiece focus should be freely used without fear.

4/ BUT the parallax cannot be precisely adjusted unless the eyepiece focus has been fairly well set for the person doing the adjusting first. So the order of adjustment will be (a) eyepiece focus (b) parallax (c) then redo eyepiece focus for whoever uses the scope. And dont allow anyone else to touch the objective focus. Tape it up if necessary for that range.


5/ If the parallax is perfectly adjusted for the range distance, and there are no abarrations in the scope, it should not matter if the image is perfectly centred or if there is some shadow on one side. BUT it is not a perfect world so its good practice to always centre the image in the eyepiece. In fact - if the image is perfectly centred - and always centred to the same spot each time - some remaining parallax will have no effect on shots. If you have to shoot a scope you know to have serious parallax errors and have no time to adjust it out it may pay to draw the eye way back and center well each shot.

6/ Finally, the parallax adjustment, as other have said, is adjusted for minimum movement of X on target as the head is moved sideways. It must NEVER be done on the basis of what looks the sharpest. This is why you never let anyone else muck about with the objective focus unless you really know they do know what they are doing. Tape over the side focus on the scope so no one can get to it.

Peter Smith

[AlanF]

....ALL quality scopes which can be focused for different ranges have parallax if not fosused properly by the shooter for the range at thich it will be used. It does not have to be adjusted by the factory...

Peter,

My statement regarding the need for factory adjustment at the end of my post relates to the situation where parallax has been eliminated, the cross-hair is in focus, but the image is not in focus i.e. to eliminate parallax, you find you need to take the image out of sharp focus. I haven't experienced this, but have seen it discussed on benchrest.com.

Alan

[pjifl]

Alan wrote,

My statement regarding the need for factory adjustment at the end of my post relates to the situation where parallax has been eliminated, the cross-hair is in focus, but the image is not in focus i.e. to eliminate parallax, you find you need to take the image out of sharp focus. I haven't experienced this, but have seen it discussed on benchrest.com.



If no aberrations are present, this can never happen. By definition - no parallax corresponds exactly to perfect focus. Thats in a perfect world.

If it can be 'adjusted out by the manufacturers' then probably some of the lenses - must likely the zoom lenses in the complex erector - are out of alignment and thus decentred. Or a poorly designed eyepiece maybe. Or a generally poor optical design which is inexcusable in this computer design age when one pays King's Ransoms for riflescopes.

Its really an optical problem - not a parallax problem - and can only be cured with better optical design/construction. The image is being smeared over a larger span rather than being constrained to an infinitely thin optical plane.

If you want to remove parallax when other aberrations are present its an impossible compromise. In this case, centering the eye/image well for each shot becomes far more important.

You can actually be quite sloppy with parallax if the eye/image are centred well each shot - but if you forget for one shot it will come back and bite you.

Peter Smith.

[AlanF]

...By definition - no parallax corresponds exactly to perfect focus...

I wondered about that, but had to wait for an expert to confirm it, which you have now done.

Here is one of the benchrest.com threads I'm referring to :

http://www.benchrest.com/forums/showthread.php?t=24858

Alan

[joliver]

Looks like I've *definitely* come to the right place!:-)

MANY thanks for all this info guys - I'm going to PRINT OUT THIS THREAD and take it with me when I go to the range - will read through it again before I start my messing around prior to that 1000 yard shoot...

I'm hoping that nothing is wrong with the scope because if I can put that one more variable behind me and assume that my rig is basically fine the way she is I can then get on with focusing on my shooting...

John.

[pjifl]

Alan, I looked at that website thread.

Much of the comment is either wrong or misleading.

'Louis Boyd' gets it right assuming perfect optics and puts it very succiently.

'Longshot1' has some relevant points.

He seems to have a mistrust of the side focus systems, however, that may be misfounded. I cannot see anything inherently wrong with sidefocus systems and they are quite tolerant to collimation errors. As pointed out by someone else, side focus systems have been used on quality theodolites for almost a century and these have accuracies an order of magnitude higher than rifle scopes. They also focus from a few feet to infinity.

But I have no idea how they are implemented mechanically inside a riflescope and maybe a locked system is better. Certainly I like a locked system for parallax. But mainly because I dont want the setting disturbed when set rather than a mistrust of collimation problems.

Some people are alweays racking the side focus. Usually in search of mirage at different focal positions. But the same effect can be obtained by focusing the eyepiece instead with no chance that the delicate parallax correction is upset. It takes time to reset parallax well and during a shoot in my oipinion is not the time to be doing it. There are enough other things to think of.

If you have a quick focus eyepiece its easy to tweak this during a shoot or search for intermediate mirage if you want. BUT it must be an unlocked quick focus eyepiece. Some will be horrified at this but in reality the eyepiece can flop around without disturbing parallax in any way.

I detest slow focus lockable eyepieces.
Two reasons.

1/ Its almost impossible to get best eye focus without quickly focusing inside and outside focus then choosing the best in between point. It needs to be done quickly or the eye will be drawn to the new focus condition so you miss the best point.

2/ If slow and locked there is a tendency to not adjust. It should be possible with a good scope for different people to get down behind it and in a few seconds adjust the eyepiece for themselves. If they dont they will not get the best out of it. And the owner of the scope should feel comfortable with this. (remember parallax is not changed). If I was the owner I would hate anyone else to be seeing a blur with my scope when a quick eyepiece focus will fix it. Only a quick focus unlocked eyepiece fulfills these conditions and allows the owner to quickly restore the best focus for themself. Some people go frantic if you suggest focusing for another eye. This is the result of either a misunderstanding of what adjusts parallax (front or side) or the result of an abortion of an eyepiece arrangement with very unfriendly focus adjustments.

The lockable eyepiece riflescope is mainly a hangover from hunting or military use where one never wants the setting to be far out even with rough use. Its different on a precision shooting range.

I got a bit off track here but hope its interesting to someone.

Peter Smith.

[AlanF]

...'Louis Boyd' gets it right assuming perfect optics and puts it very succiently...

Well actually he should get it right. He's the shooter I mentioned to you once who manages an astronomical observatory!

...Some people are alweays racking the side focus
Usually in search of mirage at different focal positions. But the same effect can be obtained by focusing the eyepiece instead with no chance that the delicate parallax correction is upset...

But wouldn't this take your cross-hair out of focus?

Alan

[pjifl]

pjifl wrote:
...Some people are alweays racking the side focus
Usually in search of mirage at different focal positions. But the same effect can be obtained by focusing the eyepiece instead with no chance that the delicate parallax correction is upset...


Alan replied
But wouldn't this take your cross-hair out of focus?


I probably was unclear on what I meant here.

Some people rack the side focus in the hope that they will pick up mirage more localized to midrange rather than the targets. But before shooting they quickly refocus again on the target attempting to restore zero parallax.

When the eyepiece focus is changed instead the X hairs will certainly defocus but the mirage focal shift is the same as above. Of course one needs to restore best focus to shoot again - the difference being that even if its not perfectly set, the parallax is still OK.

Peter Smith

[AlanF]

Now I get it.

And to support what you said about the eye-piece not needing to be locked, I found mine loose to the point of wobbling once, and it didn't appear to have been affecting accuracy.

Alan