WTH is it for?

Do I need it in a hunting situation?

What is the infinity setting for?

In a nut shell the parralex will help you focus in on objects at different ranges!

For the most part you will not need it in most hunting situations!

I seriously doubt you will ever need the infinity setting! That would be used for EXTREME shooting at like 600+ yards!

Most rifle scopes that dont have a parralex adjustment will be parralex free at 100 yards.

I own a lot of AO scopes and most of the time they will be set at 100 yards unless I know that most likely my shot will be farther than that! I have one place that I hunt where I set it at 300 yards because I fully expect my shot to be around the 300 yard mark!

If you have a parralex scope then take it out in your back yard and set the parralex to 300 yards or more and then try to focus in on something between 25-50 yards away and it will appear blurry. Now turn the AO down to about 25-50 yards and the image should become crystal clear!

Hope that helps!

Got it.

Set to 100 and hunt. If I wanna shoot long distance adjust the paralax.

Set at 100 I should be good to go from 0-100 right.

I have this on a 223 and 17hmr.

you are partly correct, if you wanna shoot long distance your scope will still be sighted for 100 yards. adjusting your parralax will only make it clear,wont change the zero!!!

I just leave mine on the infinity selection and it does the trick from 25 yds to as far as I need it.

Where the scope is adjusted for the bullets Point of Impact has nothing to do with paralax. Paralax is a function of the adjusting - or not - the focus & clarity of the crosshairs single sighting plane. As stated ...when the A/O is set for 300 yards the crosshairs are in focus at that distance with some overlap in front and behind that point. You can do the same thing with a camera and a zoom lense.
Better grade scopes with an A/O do a better job of retaining croshair clairity at a broader focal point front to rear on both sides of the set distance.

I really like to use an A/O on super short shots at teeny tiny targets like an aspirin up to about 35-50 yards...or at + 250/300 yards especially when it's hot and you are getting a lot of heat mirage and I need all the focal help I can get at seeing only the crosshairs without any fuzz to them.
Ron

Good information.

A layman's idea of parallax....

Ever see heat waves on a highway, that's caused by parallax phase of the light rays....your eyes are not able to adjust the parallax factor of the light coming from past this distortion, in theory, AO scopes would allow you to focus past minor distortions...also can help with glare on snow covered ground or near water...