Parallax I have a 10x40-50 barska varmit. The parallax adjustment changed when I was shooting, it seems to have shifted so that it is out of focus on anything over 50 yards.

Zeiss has a lifetime warranty on their conquest line. Contact Carl Zeiss Welcome ZEISS United States

That is a parallax adjustment. You set it for the distance you are shooting at. It appears to be marked in both yards and meters. This adjustment assures the reticle does not appear to move when your eye is moved slightly from side-to-side. Set it for 200 and look at a target at 50 and move your head very slightly side-to-side and you will see the difference.

Sounds like a good plan. Before you send it back make sure you are using it correctly (distance and control adjustments, including Parallax adjustment if you have one).

If you are trying to focus at a relatively close distance, you may be overpowering the scopes ability to focus at that distance. Most rifle scopes are set to parralax free at 100 yards.You can see this effect by putting the scope on its lowest power, focusing at 25-50 yards, and then increasing the power setting. You will see the image go out of focus as the power increases. This simply means that you must shoot at longer distances in order to use the scope to its full potential.

The other problem may be your parallax adjustment, but you may have already tried that solution.If not, make sure that the adjustment dial is set at the distance you are trying to shoot (minor adjustment from the indicated setting may be required to fine tune the image).

This may indicate that you have exceed the scopes ability to focus in the near distance. You don't mention the distance you are trying to shoot, but most scopes are optimized for 100 yards. At shorter distances you may be encountering parallax problems.

If these do not seem to fit your situation, I would recommend you call Nikon and get a return authorization so they can check it out for you.

This typically means that you are have exceeded the scopes ability to focus at the distance that you are shooting. This scope is optimized for 50 yards and will function well at all magnification settings. Closer than this optimal distance the higher magnifications may present problems with blurring. Many scopes have a "parallax" adjustment that changes the optical focus to correct this problem. Several of my 22 mag scopes have this adjustment on the objective bell. You simply set the indicator line on the appropriate yardage indicator (making minor adjustments to fine tune focus). Hope this helps

It is possible but not advisable. It should be done by a professional and requires special tools.
If you have a spring loaded gun, the binary recoil will destroy it in short time. If it's a PCP, you want a scope with on-the-fly adjustable parallax for range finding.

My advice would be to change this scope for a dedicated air-rifle scope.

Will it work if you back off the screws a quarter turn?

the front ring is for adjusting point of impact at a given range,,,its called a "parallax ajustment" it corrects for the scopes inaccuracies over its full range say from 10 yds to 100 yds there a bit of a pain on a hunting rifle as you need to focus them every time and that slows down your shooting, when only a snap shot will get the kill you cant wate to mess about focusing the darm scope so i never use them on my rifles,,unless im target shooing,, or im snipping when i have time to take my shot,,,
(a head shot only!) only a parallax scope is spot on aim from 10yds to infinity

It's not a high end scope. Most times you're better off buying a lower power scope of better quality and you'll still be able to see more clearly than with a higher power yet lower quality scope.

Consider that 6x, and lower power, scopes were pretty much standard for WWII snipers, and that fixed 10x is still an accepted power level for snipers these days.