Function of the AO (adjustable objective)

[Michael H]

What advantage does the AO give to the shooter?  I use the adjustable ocular to clarify my cross hair.  But, when I get the cross hair in focus the target say at 100 yds is out of focus.  Does the AO bring the target back into focus without changing the cross hair focus?
I am getting older and my eyes are not as functional as they were 20 years ago.
Someone explain this to me please. What are some of you scope fanatics suggestions or favorites with the AO option? 
One more question: What is side focus and how does this work?  

[Graybeard]

Your adjustable eyepiece is used to set cross hair focus. It's best to hold it up to the sky or a plain white wall while doing this. Don't just keep looking while turning. Turn a bit and look than turn and look. If you continue looking your eyes will focus for you and that's not what you want so look away from time to time. Once they are clear and black as can be then you've got the scope foucused.

The AO is used to remove parallax but yes if it's not correctly set for the distance you are looking at the images will blur. The markings on the AO are at best approximate but will get you in the ball park if you know the distance. Fine tune from there.