The parallax adjustment is for removing parallax by bringing the image and the reticule on the same plane. The eyepiece is for focusing on that image once it is on the same plane as the reticule. If you use the parallax adjustment to focus on the target first, you can still have parallax.
Thank you for posting that. I've had so many people try to tell me that parallax was adjusted out when you saw a clear image that I bust out laughing sometimes. If you don't adjust your eye piece when you first get the scope you'll never get the parallax right and have a clear sight picture at the same time. Even with the eyepiece correctly adjusted sometimes you still don't see a clear image when the parallax is right.
Parallax adjustment done right has helped me win many, many shooting competitions. People just don't realize that if your eye position isn't exactly right you aren't aiming right if your scope isn't set up for parallax. And that includes shorter distances too. most people think shorter distances are less prone to parallax problems which just isn't true. In fact shorter distances have far more problems with parallax to the point that if you're shooting 50 yards and your scope is actually set to shoot 35 yards you will have a terrible time trying to hit what you're shooting at.
If your scope is set up correctly you should be able to move your head around to any position and the crosshair won't budge off the target (given you aim it at the target in the first place and you make sure the rifle doesn't move when you do). Even a slight bit of movement in where your scope points is going to cost you dearly in accuracy. For shooting rimfire benchrest with a strong scope (which all benchrest shooters use) you absolutely will not win unless you have your scope set correctly.
Another thing is the comment earlier about Leuopold scopes never having a problem with parallax or anything else. The thing is that certain Leuopold scope designs have built in problems that must be corrected very often when you adjust the parallax on the scope. You have to go all the way out to infinity to get the scope back on track if you happen to screw the parallax all the way down to as close as it gets first. The parallax adjustment will not adjust all the way down as far as the scope will and it pushes it out of adjustment every time you screw the scope down to minimum magnification. That's just true and I'm sorry if it offends Leuopold scope owners. Not all of their scopes have this problem and the problem is fairly easily fixed if you know to do it. They make great scopes otherwise for the most part. But it's hard for me to sit back and let it go when someone says they have zero problems. Not true. It wouldn't stop me from buying one of their scopes but I would have to think about it first.
Parallax is one of the keys to the successes I've had shooting especially for rimfire rifles. To be honest there have been situations where I didn't freely give out this info because I knew it might cause me to lose a contest. That's been rare though. I'm posting it here now ain't I?
Trust me if you want top quality accuracy parallax is an issue you need to know about and understand and know how to fix the problems. I am giving away trade secrets here so learn it while you can.
Seriously it is a big issue.
Just for the record it generally isn't a big problem for hunting or plinking. It's only a problem for those trying to go from a .20" group to a .15" group mostly. But it can be a huge issue if your scope is seriously messed up.